Alcohol- and water-soluble bis(tpy)quaterthiophenes with phosphonium side groups: new conjugated units for metallo-supramolecular polymers

Abstract

Bis(tpy)quaterthiophenes with symmetrically distributed two and four 6-bromohexyl side groups were prepared and modified by the reaction with triethylphosphine to give the corresponding ionic species. Both ionic and non-ionic bis(tpy)quaterthiophenes (unimers) were assembled with Zn²⁺ and Fe²⁺ ions to conjugated metallo-supramolecular polymers (MSPs), of which the ionic ones are soluble in alcohols and those derived from tetrasubstituted unimers are soluble even in water. The differences in assembly are specified between systems with (i) ionic and non-ionic unimers, (ii) Zn²⁺ and Fe²⁺ ion couplers, and (iii) methanol and water solvents. A substantial decrease in the stability of Fe-MSPs and a surprisingly high red shift of the luminescence band of Zn-MSPs were observed on going from methanol to aqueous solutions.

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Introduction

Conjugated metallo-supramolecular polymers (MSPs) derived from α,ω-bis(tpy)oligoarylenes (tpy stands for 2,2′:6′,2′′-terpyridine-4′-yl end-group) are of interest as potential materials for devices with applications based on the light/electricity inter-conversion and non-linear optical phenomena (light-emitting devices, photovoltaic cells, etc.).^1–16 However, an overwhelming majority of these MSPs suffer from low solubility, which makes their processing difficult. For example, MSPs derived from α,ω-bis(tpy)oligophenylenes have been processed from acids^17,18 that surely are not optimal solvents.

Chains of conjugated MSPs of this type are composed of molecules of bisterpyridines that are linked via facial and meridian coordination of their tpy end-groups to metal ions such as Ru²⁺, Fe²⁺, Zn²⁺ and Co²⁺ (generally Mt²⁺) ions. The tpy-Mt²⁺-tpy linkages are strictly linear and rigid.^11,19–27 The enchained unimers are also quite rigid due to the delocalization of π-electrons. The rigidity of both of these constitutional units together with electrostatic repulsions of the main-chain Mt²⁺ cations favor extended conformations of MSP chains that are favorable for inter-chain attraction. Thus the above structural features can be regarded as the main reason for the low solubility of MSPs derived from α,ω-bis(tpy)oligoarylenes.

An increase in the solubility of the discussed conjugated MSPs has been achieved by introducing pendant alkyl groups into unimer units. However, this increase is insufficient.²⁸ Further improvement in the solubility of MSPs can be achieved by introducing cationic pendant groups onto unimer building blocks. The markedly cationic character of MSP chains should reduce the inter-chain attraction and thus make MSPs more soluble mainly in polar solvents such as alcohols or even in water. Such solvents are perhaps the most desired for processing of conjugated MSPs.

The above approach has been recently tested on thiophene and bithiophene with tpy end-groups.²⁹ In the present paper, we report the preparation and basic properties of α,ω-bis(tpy)quaterthiophenes with cationic side groups and related conjugated MSPs with Zn²⁺ and Fe²⁺ ion couplers. Since the studied MSPs show constitutional dynamics,^30,31 they exist in solutions as short oligomeric chains composed of starting unimers. The term unimer proposed by Ciferri³² is used in the further text for a building block of MSPs.

Results and discussion

The prepared ionic as well as non-ionic unimers and their abbreviations are shown in Chart 1 together with the numbering of the central block positions and the marking of the rings used in the assignment of NMR spectra. The letter Q denotes the unimers with the quaterthiophene central block and the numbers behind it indicate the positions occupied by hexyl groups (suffix -H) or by hexyl groups capped with a 4-methoxyphenoxy group (suffix -A) or a bromine atom (suffix -Br) or a triethylphosphonium group (suffix -P⁺). MSPs are marked with the prefix P_Zn (polymers with Zn²⁺ ion couplers) or P_Fe (Fe²⁺ ion couplers) before the unimer label: for example, P_ZnQ27-Br denotes the MSPs formed by the assembly of Zn²⁺ ions and unimer Q27-Br that contains 6-bromohexyl groups attached to the quaterthiophene central block at positions 2 and 7; P_FeQ45-P⁺ stands for the MSPs formed from Fe²⁺ ions and unimer Q45-P⁺ that contains two 6-(triethylphosphonium)hexyl groups attached to positions 4 and 5 of the central block, etc.

Chart 1 Structures and codes of the prepared unimers.

Synthesis and characterization of unimers and polymers

The reference unimers Q and Q27-H were prepared using the Suzuki–Miyaura coupling strategy (Scheme 1) and the conditions applied earlier.^28,29,33Br-unimers were prepared using the strategy shown in Schemes 1 and 2a. The starting monomer 3-[6-(4-methoxyphenoxy)hexyl]thiophene was prepared using the procedure described elsewhere.³⁴ The procedure starting from 3-(6-bromohexyl)thiophene used for the synthesis of ionic unimers with mono- (M) and bithiophene (B) central blocks²⁹ was not so effective owing to low efficiency of purification of unimers with bromohexyl groups. Connecting tpy end-groups by Suzuki coupling (Scheme 1c) was accompanied by partial dehydrobromination of bromohexyl side groups promoted with tpy end-groups.²⁹ Purification of short unimers could be done easily (for M) or feasibly (for B), but the purification of bis(tpy)quaterthiophenes was almost impossible.

Scheme 1 Synthesis pathways to the reference unimers Q and Q27-H and A-unimers.

Scheme 2 Transformation of the type A-unimers into type Br- (a) and type P⁺-unimers (b).

The use of new starting monomers avoided the above difficulties and, in addition, made the isolation of all intermediates as well as A-unimers much easier. The A-unimers were then allowed to react with BBr₃ (Scheme 2a) to give the corresponding Br-unimers with bromohexyl side groups (yield 85–95%), which were finally treated with triethylphosphine to give the corresponding ionic P⁺-unimers (Scheme 2b). Excess PEt₃ was easily removed by vacuum distillation and its oxide (POEt₃) was washed away with toluene and ether. Solid products were isolated by centrifugation (yield of the ionization step was from 75 to 95%).

Solubility in methanol was the first evidence of successful transformation of the Br- into P⁺-unimers. The NMR spectra of modified unimers accordingly showed a ³¹P signal of P⁺-groups at around 39 ppm (38.93 for Q27-P⁺, 38.44 for Q45-P⁺, 39.99 for Q2457-P⁺), ¹H signals of ethyl groups (part of P⁺) but no signal at 3.4 ppm that is typical of CH₂-Br groups. Weak ¹H signals at 5.93 ppm and 5.55–5.45 ppm were also observed indicating that some side chains contain terminal double bonds formed by dehydrobromination accompanying quaternization of Br-unimers. Complete removal of imperfect molecules from P⁺-unimers was not successful since they are soluble in alcohols.

TGA analyses of Br-unimers and P⁺-unimers showed thermal stability up to 205 °C.

Metallo-supramolecular polymers were simply prepared by mixing solutions of a given unimer and zinc(II) or iron(II) perchlorate in the metal ions to a unimer mole ratio of r = 1 (r = [Mt²⁺]/[unimer]). Br-unimers were assembled in the acetonitrile/chloroform mixed solvent (1/1 by vol.) while P⁺-unimers were assembled in methanol.

The solubility of the prepared unimers and polymers depends on the substitution of the unimer central block. The unsubstituted unimer Q is soluble in dichloromethane but poorly soluble in chloroform. Br-unimers are highly soluble in solvents such as THF, CHCl₃, CH₂Cl₂, DMSO and the acetonitrile/chloroform mixture, which facilitates their isolation and purification. Unimers with two ionic groups are highly soluble in polar solvents such as methanol, ethanol and DMSO and sparingly soluble in water (complete dissolution to a colloidal solution takes a few weeks). Unimer Q2457-P⁺ carrying four ionic groups is easily soluble in water, which is quite unusual for this type of conjugated structure. Nevertheless, complete dissolution of Q2457-P⁺ to the molecular level takes time on the day scale as can be seen from the time development of the UV/vis spectrum of its aqueous solution shown in Fig. S1, ESI.† MSPs show similar solubility to the corresponding unimers.

Vibrational spectra of unimers and polymers

The IR spectra of unimers show each the bands of stretching modes (ν_CC, ν_CN) of tpy end-groups (1500–1620 cm⁻¹), the quaterthiophene central block (1370–1500 cm⁻¹), aromatic ν_CH modes (3000–3100 cm⁻¹) and the main out-of-plane modes (ρ_CH) of aromatic moieties (790 and 658 cm⁻¹) at nearly identical positions (Fig. S2, ESI†). Differences due to different substitutions of the central blocks are mainly seen in the fingerprint region from 850 to 1350 cm⁻¹. The presence of hexyl chains is mainly observable in the C–H stretching region (2800–3000 cm⁻¹). The most intensive bands characteristic of vibrations of hexyl groups in the fingerprint region (1466 and 1379 cm⁻¹) are overlapped by the ring stretching modes of the quaterthiophene central blocks. Only a small shift of the band maximum from 1459 cm⁻¹ (for Q) to 1466 cm⁻¹ (for Q27-H) and a new shoulder at 1384 cm⁻¹ for Q27-H are observable. The broad spectral band at 3400 cm⁻¹ observed for all P⁺-unimers is due to the presence of hydrogen bonded water molecules in these unimers.

The off-resonance Raman spectra of unimers show strong stretching bands of quaterthiophene blocks but weak bands of tpy end-groups. Their spectral patterns reflect differences in the substitution of quaterthiophene blocks (Fig. S3, ESI†). The Raman spectra of Zn-polymers were disturbed by strong fluorescence but spectra of non-fluorescent Fe-polymers were well measurable. The bands characteristic of tpy groups³⁵ occur at 1610 cm⁻¹ (ν_s), 1290 cm⁻¹ (δ_ip) and 1038 cm⁻¹ (breathing mode) while the bands of quaterthiophene blocks^36–38 occur in the region 1380–1520 cm⁻¹ (Fig. S4a–S7a, ESI†). Deconvolution of the latter band using the OMNIC software gave robust results, showing that this band is composed of at least five bands (Fig. S4b–S7b, ESI†) whose intensities depend on the positions of side groups. The band at 1472 cm⁻¹ should also be attributed to transitions in tpy groups.³⁵

Optical spectra of unimers and polymers

The solution UV/vis absorption spectra of unimers (ESI, Fig. S8a†) show: (i) a flat band at 280–284 nm mainly contributed by transitions in tpy end groups, and (ii) a band with the apex at a wavelength λ_A from 381 nm (Q2457-P⁺) to 441 nm (Q) belonging to transitions from HOMO that is spread over thiophene rings and central rings of tpy groups.^28,33 The value of λ_A (see Table 1) decreases (i) with increasing distortion of the quaterthiophene central block (see Table 2), and (ii) on going from the non-ionic (-Br, -H) to ionic unimer (-P⁺) of the same type. Absorption maxima in the spectra of unimer thin films (ESI, Fig. S8b†) are not in such good correlation with the chain distortion, which reflects the importance of the molecular packing effect or the electronic effect of substituents. An exceptionally high λ_A of Q2457-Br thin films (500 ± 10 nm) was obtained. The fact that Q2457-P⁺ shows much lower λ_A can be ascribed to the bulkiness of P⁺Et₃ groups and the effect of bromine counterions.

Table 1 UV/vis and luminescence spectral characteristics of the prepared unimers and polymers; solvent: methanol for ionic unimers and polymers (suffix -P⁺); acetonitrile/chloroform (1/1 by vol.) for all the other unimers and polymers. λ_A – apex of absorbance maxima; λ_F – apex of emission maxima; ν – Stokes shift; λ_MLCT – apex of the MLCT band; Φ – absolute luminescence quantum yield

Sample	UV/vis absorption		Luminescence		Stokes shift
	λ A, nm		λ F, nm (Φ, %)		ν, cm^−1
	Solution	Film	Solution	Film	Solution	Film
Q	441	425	514, 546 (30%)	645 (<1%)	4350	7450
Q27-H	425	460	554 (26%)	630 (1%)	5500	5300
Q27-Br	425	455	554 (31%)	630 (1%)	5500	6000
Q27-P^+	419	455	550 (18%)	∼650 (<1%)	5700	7300
Q45-Br	397	425	530 (14%)	610 (1%)	6300	7000
Q45-P^+	393	410	536 (11%)	550 (1%)	6800	6200
Q2457-Br	386	500	536 (14%)	560, 603 (3%)	7250	3600
Q2457-P^+	381	410	536 (10%)	560 (1%)	7600	6400
Q2457-P^+ ^a	400		555		6980
Zn polymers
P Zn Q	486	500	656	∼690 (1%)	5350	5050
P Zn Q27-H	468	490	673	∼640 (2%)	6500	5250
P Zn Q27-Br	470	510	675	∼710 (1%)	6450	5450
P Zn Q27-P ^+	483	500	550	∼705 (<1%)	2500	5700
P Zn Q45-Br	447	455	673	585 (3%)	7500	4850
P Zn Q45-P ^+	426	430	536	660 (1%)	4800	8050
P Zn Q2457-Br	432	430	668	590 (3%)	8200	5800
P Zn Q2457-P ^+	439	440	552	625 (1%)	4650	6450
P Zn Q2457-P ^+	462^a		720^a		7750^a

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Fe polymers
	UV/vis absorption
	λ A, nm, (λMLCT, nm)
	Solution	Film
a Data from aqueous solution. b Shoulder.
P Fe Q	395, 471 (603)	475 (621)
P Fe Q27-H	437 (601)	460 (622)
P Fe Q27-Br	387, 452 (601)	465 (621)
P Fe Q27-P ^+	386, 436 (593)	465 (611)
P Fe Q45-Br	405 (598)	410 (613)
P Fe Q45-P ^+	399 (593)	410 (609)
P Fe Q2457-Br	384, 423sh, (594)	395^b (609)
P Fe Q2457-P ^+	384 (591)	395^b (604)
P Fe Q2457-P ^+	400 (607)^a

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Table 2 Calculated geometry of the unimers; δ_BC⋯δ_DD′ are dihedral angles between the planes of neighbouring main-chain rings given in subscript (for ring labels see Chart 1)

	Ground state			Excited state
	δ BC	δ CD	δ DD′	δ BC	δ CD	δ DD′
a Values are not available for the first 720 hours.
Q	15.8	12.5	0.7	0.0	0.0	0.0
Q27-H	17.3	28.6	1.0	0.0	0.0	0.0
Q27-Br	13.9	22.8	1.0	0.5	3.2	1.3
Q27-P^+·Br^−	17.3	32.4	16.3
Q45-Br	14.6	18.5	58.9	1.4	3.1	23.7
Q45-P^+·Br^−	18.0	15.4	63.5
Q2457-Br	19.6	40.8	97.5
Q2457-P^+·Br^−	15.8	27.4	124.4

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In the spectra of Zn-polymers, the absorption band of transitions involving quaterthiophene blocks is red shifted by about 35–65 nm compared to its position λ_A for the unimer in the solution spectra and by about 20–75 nm in thin films (Table 1). The only but great exception is the spectrum of P_ZnQ2457-Br thin films that surprisingly shows a blue shift of λ_A of about −70 nm, which is obviously due to the exceptionally high value of λ_A of the unimer Q2457-Br.

The spectra of Fe-polymers contain a new band belonging to transitions in the metal-to-ligand charge transfer (MLCT) complex which is typical of tpy-Fe-tpy linkages^35,39 (see Table 1 and Fig. S8c and S8d in the ESI†). In Fe-polymers, this band is significantly contributed by transitions involving neighboring oligothiophene blocks.²⁹

Luminescence spectra of unimers in solutions (ESI, Fig. S9a†) show higher similarity than their UV/vis spectra (λ_F around 550 nm; lowered values of about 535 nm are actually given by different band shapes). This is obviously due to the fast transition of excited unimer molecules to nearly coplanar conformations with quinoidal rings, from which the light emission takes place.³⁶ Minor differences are nevertheless seen: unimers with less distorted chains (Q, Q27-H, Q27-Br and Q27-P⁺) show a better resolved vibrational structure than unimers with more distorted chains (Q45-Br, Q45-P⁺, Q2457-Br and Q2457-P⁺). The luminescence spectra of unimers and Zn-polymer thin films are shown in ESI, Fig. S9b–d† and the band wavelengths are summarized in Table 1, and the luminescence lifetimes are presented in ESI, Table S1.† Fe-polymers do not show luminescence.^28,29,36

Assembly of unimers to metallo-supramolecular polymers in solutions

The assembly in solutions was monitored by UV/vis and luminescence spectroscopy, viscometry and size exclusion chromatography (SEC). A chloroform/acetonitrile mixed solvent (1/1 by volume) was used for Br-unimers while methanol and water were used for P⁺-unimers. For spectroscopic studies, a set of solutions of a constant unimer concentration (2 × 10⁻⁵ M) and a stepwise increasing metal ions to unimer mole ratio (r from 0 to 3) was prepared for each Mt²⁺/unimer system and solutions were allowed to equilibrate for 24 hours before monitoring the spectra. The SEC and viscometric measurements were done with solutions of the concentration of 5 × 10⁻⁴ M.

Spectral changes accompanying the assembly of unimers with Mt²⁺ ions showed three stages differing in the development trend, similarly to the related systems studied recently.^{21,25,28,29,40} The UV/vis spectra obtained for systems of composition ratios r from 0 to ca. 0.5 (the first stage of assembly) showed up to three isosbestic points (see examples in Fig. 1a and 2a and a complete set of the spectra in ESI, Fig. S10 and S11†), which indicates the transformation of the unimer species into another well-defined species. Regarding the stoichiometry, the new species should be a dimer species unimer-Mt²⁺-unimer.

Fig. 1 Changes in UV/vis spectra accompanying the titration of ionic unimers with Zn²⁺ ions. Initial unimer concentration 2 × 10⁻⁵ M in methanol, room temperature. Column (a) shows the first stage of assembly, column (b) shows the second stage and column (c) shows the third stage; see the text.

Fig. 2 Changes in UV/vis spectra accompanying the titration of ionic unimers with Fe²⁺ ions. Initial unimer concentration 2 × 10⁻⁵ M in methanol, room temperature. Column (a) shows the first stage of assembly, column (b) shows the second stage and column (c) shows the third stage; see the text.

The spectra obtained for systems with ratios r from ca. 0.6 to 1 also show isosbestic points but at different wavelengths (Fig. 1b and 2b). This indicates that the systems entered the second stage of assembly in which longer polymer chains are formed. As can be seen from ESI, Fig. S10 and S11,† the absorption bands characteristic of free unimers and dimers disappear while the band of enchained unimer units fully develops in the case of systems with non-ionic Br-unimers. These systems then enter the third stage of assembly (r > 1), where spectral changes are quite low and can be attributed to the end-capping of polymer chains with the metal ions and partial depolymerization of the polymer chains to the shorter also end-capped ones (Fig. 1c and 2c). The reaction of (tpy)₂Zn²⁺ species with Zn²⁺ ions giving two (tpy)Zn²⁺ species has been reported for mono- as well as bis(tpy) species.^18,29,41,42 The reaction of (tpy)₂Fe²⁺ species with Fe²⁺ ions giving two (tpy)Fe²⁺ species was reported only for metallo-supramolecular polymers.^18,29,43

The spectral changes in the second stage of assembly of ionic P⁺-unimers are less progressive than those in the case of Br-unimers or even incomplete, which indicates lowered thermodynamic stability (i.e., stability constants) of ionic polymers in methanol. The lowered stability of ionic Fe-polymers is also seen from the changes in the position and intensity of the MLCT band (at around 595 nm) that is not fully developed at the ratio r ≅ 1 (Fig. 2b). The UV/vis spectral patterns indicate that the ionic polymers acquire their maximum length at the ratios r of about 1.5 or higher in methanol solutions.

The changes in luminescence spectra accompanying the assembly of ionic unimers with Zn²⁺ ions are shown in Fig. 3. The complexation is manifested by the disappearance of the unimer emission band and the creation of a new band red shifted by about 130 nm. Unlike the case of shorter ionic polymers derived from bis(tpy) mono- and bithiophenes,²⁹ the new emission band is much less intense than the band of free unimers. A similar luminescence attenuation is also exhibited by systems with non-ionic polymers. This shows that the prolongation of the unimer central oligothiophene block increases the efficiency of non-radiative paths of the decay of excited states in Zn-polymers.

Fig. 3 Changes in photoluminescence spectra accompanying the titration of ionic unimers with Zn²⁺ ions. Initial unimer concentration 2 × 10⁻⁵ M in methanol, room temperature.

Unlike the systems with Zn²⁺ ions, those with Fe²⁺ ions show a monotonous luminescence quenching with increasing ratios r up to ca. 0.6, at which the luminescence disappears (for example see ESI, Fig. S12†). This behaviour, which is exhibited by other systems with bis(tpy)Fe²⁺ species, is attributed to the fact that the lowest excited state of bis(tpy)Fe²⁺ species, the d–d triplet state, is close to the ground state.⁴⁴ As the d–d triplet state easily depletes higher excited states and potential phosphorescence from the d–d state is spin forbidden, its decay by non-radiative transitions is unambiguously preferred in accord with the energy gap law.^8,45

The molar mass distribution of Br-polymers in CHCl₃/CH₃CN (1 : 1) solutions was examined using an SEC system equipped with a diode-array UV/vis detector (DAD). (Analysis of ionic polymers failed owing to the strong adsorption of their chains inside SEC columns.) Mixed solutions of a Br-unimer (0.5 mM) and Zn²⁺ or Fe²⁺ ions (r from 0 to 2.0) equilibrated for one day were injected into the SEC system. The SEC records of systems with Zn²⁺ ions showed nothing but the peak of free unimers, which proves rapid dissociation of the Zn-polymer chains upon multifold dilution of their solution inside SEC columns. In contrast, the systems with Fe²⁺ ions provided SEC records typical of covalent polymers (Fig. 4 and ESI, S13†), which demonstrates very slow constitutional dynamics of Fe-polymers in the used solvent. Similar results were recently obtained for MSPs of shorter bis(tpy)thiophenes.²⁹

Fig. 4 The SEC records of the Fe²⁺/Q45-Br systems of different compositions.

Well resolved SEC records were obtained only for systems with a composition ratio r < 1 (Fig. 4). Systems with r ≥ 1 gave poorly resolved SEC records, in which the area under the elution peak decreased with increasing value of r. This indicates retention of longer chains in SEC columns. The detained polymer chains, obviously end-capped with Fe²⁺ ions, had to be additionally washed out of the columns with 2,2′-bipyridine. The UV/vis spectral pattern of SEC fractions showed a perfect development with the elution time (t_el): a pattern typical of long polymer chains was observed for the first eluted SEC fractions while that typical of the dimers for the last fraction (Fig. 5a and ESI, Fig. S14a†). Differences are also seen when comparing the spectra of fractions of dimers formed in systems of different compositions (Fig. 5b and ESI, Fig. S14b†). These differences can be attributed to the end-capping of their molecules with Fe²⁺ ions. However, these differences are substantially smaller than those observed for the Fe-polymers formed from unimers with mono- and bithiophene central blocks.²⁹

Fig. 5 The UV/vis DAD spectra of SEC fractions of the Fe²⁺/Q45-Br system (r = 0.8) eluted at different elution times t_el (a) and comparison of the spectra of the last fraction (dimers; t_el = 1470 s) of systems of composition r from 0.2 to 1.0 (b).

The presence of higher fractions in solutions containing a stoichiometric lack of Fe²⁺ ions (r = 0.2 and 0.5) can be explained by the transiently locally increased concentration of the ions and unimers during mixing of their solutions. The formation of polymer chains is most likely a kinetically controlled process which, on mixing twenty five times more concentrated solutions (0.5 mM instead of 0.02 mM), shall be ca. 625 times accelerated. Thus it can give rise to a significant number of longer chains that do not dissociate during the SEC analysis thanks to their slow constitutional dynamics. Thus the degree of polymerization, X, of Fe-polymer chains in solution could be estimated. If the peak eluted at t_el = 1460 s (see Fig. 4) is ascribed to dimers, the peak with t_el = 1305 s to trimers, and so on, one can still resolve the peak of heptamers at t_el = 1114 s. Calculations based on this peak assignment provide the weight-average degree of polymerization equal to ca. 7 for Fe-polymer in the solution with r ≅ 1 (Table 3). In addition, it is seen from Fig. 4 that the stoichiometric excess of Fe²⁺ ions in solution results in the formation of shorter chains. The latter is supported by the results of viscometric measurements, which also indicate shortening of the polymer chains in the presence of excess Fe²⁺ ions (ESI, Fig. S15†).

Table 3 Number-average (X_n) and weight-average (X_w) degrees of polymerization and dispersity index (Đ) of P_FeQ45-Br in solution calculated from SEC records

r	X n	X w	Đ
0.2	3.07	4.23	1.36
0.5	3.24	4.77	1.47
0.8	4.43	6.02	1.36
1.0	6.13	7.23	1.18
1.05	6.79	7.62	1.12
1.25	6.26	6.84	1.09

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Assembly of Q2457-P⁺ in water

The water-soluble unimer Q2457-P⁺ has been assembled with metal ions also in aqueous solutions. Since molecular dissolution of this unimer in water takes a long time a month-old solution of Q2457-P⁺ was used in these experiments. As can be seen from Fig. 6, the optical spectral changes accompanying the assembly in water substantially differ from those observed for assembly in methanol.

Fig. 6 Changes in UV/vis (left column) and photoluminescence (right column) spectra accompanying the titration of ionic unimers with Zn²⁺ or Fe²⁺ ions. Initial unimer concentration 2 × 10⁻⁵ M in water, room temperature.

(i) The absorption maxima of Q2457-P⁺ (λ_A = 400 nm) and its Zn-polymer (r = 2, λ_A = 462 nm) as well as the luminescence maximum of the unimer (λ_F = 555 nm) are red shifted by about ca. 20 nm compared to their positions in methanol solutions, which indicates that the free as well as enchained unimer species acquire more planar conformations in water than in methanol. This can be attributed to the substantial increase in the solvent permittivity, which, in accord with the Coulomb law, reduces repulsive ionic interactions among neighbouring P⁺Et₃ groups as well as their attractive interactions with counterions.

(ii) The luminescence emission band observed for Zn-polymer (λ_F = 720 nm) is enormously red shifted (about 168 nm) compared to the band for methanol solution. The Stokes shift for P_ZnQ2457-P⁺ in water (7750 cm⁻¹) is much higher than the shift in methanol (4650 cm⁻¹, Table 1), which proves the much higher extent of conformational relaxation of excited states in aqueous compared to methanol solutions.

(iii) The UV/vis spectra for assembly of Q2457-P⁺ with Zn²⁺ ions show a single set of isosbestic points and a fluent course of changes up to r = 2. Luminescence spectra indicate the presence of free unimers in solution with r equal to at least 1.5. These features consistently indicate a lowered stability and increased constitutional dynamics of P_ZnQ2457-P⁺ in aqueous solutions.

(iv) Surprisingly, in accord with the last mentioned observations, the UV/vis spectra for assembly of Q2457-P⁺ with Fe²⁺ ions show small changes and a weak MLCT band and the luminescence spectra show emission even at the composition ratio r = 3. It should be stressed here that no new emission band occurs; only reluctant luminescence quenching with increasing r is observed. The observed spectral changes indicate that the chains of a highly ionic Fe-polymer are, in aqueous solution, less stable than the chains of its Zn-counterpart. This observation represents a flip in the stability of Fe- and Zn-polymers derived from bis(tpy)quaterthiophenes compared to perhaps all the data reported so far.^41,46–49 The reduced stability of the ionic Fe-polymer in water is obviously associated with the inhibition of the MLCT process by water. The solvent dependence of the MLCT is well known.^50,51

Conclusions

The synthesis strategy developed here enables preparation of bis(tpy)quaterthiophenes with two or four side groups symmetrically distributed along the quaterthiophene central block. The modification of side groups enabled preparation of ionic unimers that are soluble in green solvents such as alcohols or even in water.

Optical spectral patterns of dissolved unimers and the corresponding polymers depend primarily on the distribution of side groups along the quaterthiophene central block and only secondarily on the nature of side-chain-capping groups. The effect of the latter is more apparent in the solid state spectra since the capping groups significantly influence molecular packing.

During the assembly of unimers with metal ions the development of UV/vis spectra with increasing ratio r conclusively indicates that the P⁺-unimers assemble with metal ions less readily than the Br-unimers. Besides, in water, Q2457-P⁺ assembles with Zn²⁺ ions considerably less progressively (with rising r) than in methanol and, with Fe²⁺ ions, still much less readily, showing only a very weak MLCT band but significant luminescence of the free unimer even at the ratio r = 3. The solvation effect is thus obvious. A red shift of the luminescence band of P_ZnQ2457-P⁺ by about ca. 170 nm on going from methanol to aqueous solution is observed. Such a big shift indicates much higher conformational freedom of P_ZnQ2457-P⁺ chains in aqueous compared to methanol solutions.

The SEC study of the non-ionic polymers proved that the constitutional dynamics of Zn-polymers is fast and that of Fe-polymers is very slow in the chloroform/acetonitrile mixed solvent, which is in accord with observations of other authors on related systems. However, the results obtained here on assembly of the ionic unimers in aqueous solutions anticipate faster constitutional dynamics of Fe-polymers compared to Zn-polymers.

Experimental section

Materials

2,2′-Bithiophene-5-boronic acid pinacol ester, 2,2′-bithiophene-5,5′-diboronic acid bis(pinacol) ester, thiophene-2-boronic acid pinacol ester, 3,3′′′-dihexyl-2,2′:5′,2′′:5′′,2′′′-quaterthiophene, bis(pinacolato)diboron (B₂pin₂), 4,4,5,5-tetramethyl-1,3,2-dioxaborolane (HBpin), 4,4′-di-tert-butyl-2,2′-dipyridyl (dtbpy), bis(1,5-cyclooctadiene)di-μ-methoxydiiridium(I) ([Ir(OMe)(COD)]₂), boron tribromide (BBr₃), triethylphosphine (PEt₃, 1.0 M in THF), N-bromosuccinimide (NBS), [1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene](3-chloropyridyl)palladium(II) dichloride (PEPPSI-IPr), zinc perchlorate hexahydrate, iron(II) perchlorate hydrate and tetrabutylammonium hexafluorophosphate (all Aldrich), K₂CO₃, MgSO₄, acetic acid (Lachner) and 4′-bromo-2,2′:6′2′′-terpyridine (TCI) were used as received. Hexane (Lachner) was stored over a molecular sieve, tetrahydrofuran (Aldrich) was distilled from LiAlH₄ before use, toluene (Lachner) was distilled from sodium/benzophenone before use, methanol (Aldrich) was bubbled with argon before use, and diethylether, dichloromethane, chloroform (Lachner) and acetonitrile (ACN) were used as obtained.

Measurements

¹H and ¹³C NMR spectra were recorded on a Varian ^UNITYINOVA 400 or a Varian SYSTEM 300 instrument in d₈-THF, d₂-CD₂Cl₂, d-CDCl₃, d₆-DMSO or d₄-CD₃OD and referenced to the solvent signal: 7.25 ppm (d-CDCl₃), 5.32 ppm (d₂-CD₂Cl₂), 3.58 ppm (d₈-THF), 2.50 ppm (d₆-DMSO) or 3.31 ppm (d₄-CD₃OD) for ¹H and 77.0 ppm (d-CDCl₃), 53.84 ppm (d₂-CD₂Cl₂), 67.57 ppm (d₈-THF) or 49.15 ppm (d₄-CD₃OD) for ¹³C spectra. Coupling constants, J (in Hz), were obtained by the first-order analysis. Infrared spectra were recorded on a Thermo Nicolet 7600 FTIR spectrometer equipped with a Spectra Tech InspectIR Plus microscopic accessory using KBr-diluted samples and the diffuse reflectance technique (DRIFT) (128 or more scans at a resolution of 4 cm⁻¹). Raman spectra of solid samples were recorded on a DXR Raman microscope (Thermo Scientific) using excitations across the whole visible region (λ_ex = 445, 532, 633 and 780 nm) and the usual laser power at the sample of 0.1–0.4 mW. UV/vis spectra were recorded on a Shimadzu UV-2401PC instrument or a SPECORD instrument in methanol or CHCl₃/ACN (1/1, v/v); solid samples were coated on the surface of a quartz cuvette. Photoluminescence spectra were recorded on a Fluorolog 3-22 Jobin Yvon Spex instrument, using a four-window quartz cuvette (1 cm) for solutions and using quartz glass for films. The emission spectra were recorded with the excitation wavelength, λ_ex, matching the absorption maximum of the measured compound. Quantum yields, λ_F, of photoluminescence were measured using the integration sphere Quanta-φ F-3029. Fluorescence decay was monitored with a FluoroHub single photon counting controller on a Fluorolog 3-22 Jobin Yvon Spex instrument using excitation at λ_ex = 378 nm for solutions and λ_ex = 472 nm for films. Viscometric measurements were performed on a Microviscometer Lovis 2000 M/Me (Anton Paar). SEC records were obtained using a Spectra Physics Analytical HPLC pump P1000 with two SEC columns: Polymer Labs (Bristol, USA) Mixed-D and Mixed-E. The system was equipped with a Thermo UV6000 DAD detector. 0.05 M tetrabutylammonium hexafluorophosphate in CHCl₃/ACN (1/1, v/v, CHROMASOLV, Riedel-deHaen) was used as an eluent (0.7 mL min⁻¹).

5-(2,2′:6′,2′′-Terpyridine-4′-yl)-2,2′-bithiophene. 2,2′-Bithiophene-5-boronic acid pinacol ester (0.509 g, 1.74 mmol), Brtpy (0.439 g, 1.41 mmol), K₂CO₃ (0.59 g, 4.26 mmol) and PEPPSI-IPr (50 mg) were placed in a Schlenk tube. Vacuum–argon cycles were applied several times and toluene (10 mL) and methanol (10 mL) were added through the septum. The reaction mixture was heated at 90 °C overnight. After cooling to room temperature the reaction mixture was diluted with dichloromethane (50 ml) and washed with water (3 × 200 mL). The organic layer was dried with MgSO₄, filtered and evaporated to obtain the crude product. The crude product was contaminated with bithiophene, which was washed off with hexane to obtain the pure product as a yellow powder (0.53 g, 95%). ¹H NMR (400 MHz, d₂-CD₂Cl₂) δ ppm 8.74–8.72 (m, 2H, A⁶), 8.70 (s, 2H, B³), 8.67–8.65 (m, 2H, A³), 7.90 (td, 2H, J₁ = 7.7, J₂ = 1.7, A⁴), 7.73–7.71 (m, 1H, C⁴), 7.40–7.37 (m, 2H, A⁵), 7.33–7.31 (m, 2H, C³ + D⁵), 7.29 (d, J = 3.8, 1H, D³), 7.10–7.08 (m, 1H, D⁴). ¹³C NMR (101 MHz, d₂-CD₂Cl₂) δ ppm 156.49, 156.10, 149.48, 143.11, 141.15, 140.61, 139.30, 137.15, 128.39, 126.89, 125.53, 125.10, 124.69, 124.32, 121.36, 116.71. IR (DRIFT), cm⁻¹ 3086 (m), 3066 (m), 3013 (m), 2988 (w), 2965 (w), 2922 (m), 2871 (w), 2856 (w), 1598 (s), 1583 (s), 1565 (s), 1553 (m), 1541 (m), 1509 (m), 1464 (s), 1435 (m), 1422 (m), 1399 (s), 1366 (w), 1353 (w), 1323 (w), 1306 (w), 1290 (w), 1267 (m), 1253 (w), 1239 (m), 1232 (m), 1227 (m), 1209 (w), 1184 (w), 1162 (w), 1146 (w), 1124 (m), 1092 (m), 1077 (w), 1064 (m), 1051 (m), 1044 (m), 1010 (m), 988 (m), 961 (w), 954 (w), 915 (w), 898 (w), 885 (m), 878 (m), 838 (m), 789 (s), 773 (m), 746 (m), 741 (m), 730 (m), 717 (s), 690 (m), 683 (m), 668 (m), 658 (m), 643 (w), 632 (m), 622 (m), 587 (w), 565 (w), 523 (m), 489 (m), 466 (m), 447 (w), 418 (w), 402 (m). HRMS found m/z: 420.05998 [M⁺Na]⁺, C₂₃H₁₅N₃NaS₂ requires: 420.05996.

5-Bromo-5′-(2,2′:6′,2′′-terpyridine-4′-yl)-2,2′-bithiophene. 5-(2,2′:6′,2′′-Terpyridine-4′-yl)-2,2′-bithiophene (0.52 g, 1.31 mmol) was dissolved in dichloromethane (20 mL) and acetic acid (20 mL), and NBS (0.26 g, 1.46 mmol) was added in the dark and the reaction mixture was stirred overnight. Then the acidic mixture was slightly neutralized by using a saturated solution of K₂CO₃ in water, diluted with dichloromethane (40 mL) and washed with water (3 × 250 mL). The organic layer was dried with MgSO₄, filtered and evaporated to obtain the product as a yellow solid (0.52 g, 83%). ¹H NMR (400 MHz, d₂-CD₂Cl₂) δ ppm 8.74–8.72 (m, 2H, A⁶), 8.68–8.65 (m, 4H, A³ + B³), 7.90 (td, J₁ = 7.8, J₂ = 1.8, 2H, A⁴), 7.71 (d, J = 3.8, 1H, C⁴), 7.38 (ddd, J₁ = 7.5, J₂ = 4.8, J₃ = 1.2, 2H, A⁵), 7.23 (d, J = 3.8, C³), 7.07–7.05 (m, 2H, D³ + D⁴). ¹³C NMR (101 MHz, d₂-CD₂Cl₂) δ ppm 156.80, 156.30, 149.77, 143.19, 139.04, 138.35, 137.46, 133.99, 131.67, 128.78, 127.18, 125.01, 124.60, 121.67, 121.62, 117.06. IR (DRIFT), cm⁻¹ 3091 (m), 3072 (m), 3061 (m), 3051 (m), 3013 (m), 2990 (w), 2962 (m), 2926 (m), 2855 (m), 1735 (w), 1600 (m), 1584 (s), 1566 (s), 1553 (w), 1547 (m), 1515 (m), 1477 (m), 1467 (s), 1438 (w), 1428 (m), 1399 (s), 1369 (w), 1340 (w), 1265 (m), 1237 (m), 1223 (w), 1206 (w), 1196 (w), 1148 (m), 1127 (m), 1100 (m), 1079 (w), 1067 (m), 1042 (m), 1010 (m), 987 (m), 973 (m), 958 (w), 906 (w), 889 (w), 880 (s), 874 (s), 849 (w), 785 (s), 773 (m), 752 (m), 743 (m), 729 (m), 690 (m), 669 (m), 659 (m), 632 (m), 622 (m), 581 (w), 556 (w), 526 (m), 495 (m), 474 (m), 455 (m), 439 (w), 414 (m), 406 (m). HRMS found m/z: 475.98846 [M⁺H]⁺, C₂₃H₁₅N₃BrS₂ requires: 475.98853.

5,5′′′-Bis(2,2′:6′,2′′-terpyridine-4′-yl)-2,2′:5′,2′′:5′′,2′′′-quaterthiophene Q. 5-Bromo-5′-(2,2′:6′,2′′-terpyridine-4′-yl)-2,2′-bithiophene (0.372 g, 0.78 mmol), B₂pin₂ (0.168 g, 0.66 mmol), K₂CO₃ (0.34 g, 2.46 mmol) and PEPPSI-IPr (25 mg) were placed in a Schlenk tube and vacuum–argon cycles were applied. Then toluene (15 mL) and methanol (15 mL) were added through the septum and the reaction mixture was heated at 90 °C overnight. After cooling to room temperature the product precipitated. The suspension was filtered, washed with toluene, water and hexane and dried in vacuo. Orange powder (0.18 g, 58%). ¹H NMR (400 MHz, d₂-CD₂Cl₂) δ ppm 8.75–8.74 (m, 4H, A⁶), 8.71–8.66 (m, 8H, A³ + B³), 7.91 (td, J₁ = 7.7, J₂ = 1.8, 4H, A⁴), 7.75 (d, J = 3.9, 2H, C⁴), 7.41–7.38 (m, 4H, A⁵), 7.35 (d, J = 4.3, 2H, C³), 7.32–7.21 (m, 4H, D³ + D⁴). Due to the low solubility of this compound we were not able to obtain the ¹³C NMR spectrum in a sufficient quality. IR (DRIFT), cm⁻¹ 3064 (m), 3012 (m), 2991 (w), 2937 (w), 1718 (w), 1599 (s), 1582 (s), 1567 (s), 1551 (s), 1508 (w), 1476 (m), 1466 (m), 1459 (m), 1438 (m), 1400 (m), 1365 (w), 1327 (w), 1308 (w), 1292 (w), 1266 (w), 1251 (w), 1237 (w), 1208 (w), 1126 (m), 1094 (m), 1079 (w), 1065 (m), 1042 (m), 1011 (m), 988 (m), 963 (w), 919 (w), 898 (w), 872 (m), 855 (w), 849 (w), 786 (s), 742 (s), 732 (m), 726 (m), 690 (m), 683 (m), 667 (m), 660 (m), 640 (m), 633 (m), 621 (m), 564 (w), 518 (w), 493 (m), 485 (w), 466 (m), 408 (m). HRMS found m/z: 793.13281 [M⁺H]⁺, C₄₆H₂₉N₆S₄ requires: 793.13310.

3,3′′′-Dihexyl-(2,2′:5′,2′′:5′′,2′′′-quaterthiophene-5,5′′′-diyl)-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolane). 3,3′′′-Dihexyl-2,2′:5′,2′′:5′′,2′′′-quaterthiophene (0.6 g, 1.2 mmol), dtbpy (15 mg, 0.0056 mmol) and ([Ir(OMe)(COD)]₂) (18 mg, 0.00271 mmol) were placed in a Schlenk tube and vacuum–argon cycles were applied. Tetrahydrofuran (20 mL), hexane (20 mL) and HBpin (0.7 mL, 0.62 g, 4.9 mmol) were added and the reaction mixture was heated to 45° overnight. Then the reaction mixture was poured into water and extracted with dichloromethane. The organic fraction was collected, dried with MgSO₄, filtered and evaporated to obtain the product as brownish oil. The product was used without further purification. ¹H NMR (300 MHz, d-CDCl₃) δ ppm 7.47 (s, 2H, C⁴), 7.15 (d, J = 3.9, 2H, D³ or D⁴), 7.10 (d, J = 3.9, 2H, D⁴ or D³), 2.79 (t, J = 7.8, 4H, Hex¹), 1.72–1.59 (m, 8H, Hex² + Hex³), 1.40–1.25 (m, 32H, Hex⁴ + Hex⁵ + –CH₃ pinacol ester), 0.92–0.87 (m, 4H, Hex⁶). ¹³C NMR (101 MHz, d₈-THF) δ ppm 141.79, 141.15, 138.20, 138.04, 136.54, 127.89, 125.34, 84.92, 32.80, 31.70, 30.32, 30.16, 25.24, 23.66, 14.6. ¹¹B NMR (128.3 MHz, d₈-THF) δ ppm 24.19. IR (DRIFT), cm⁻¹ 3062 (w), 2976 (m), 2956 (m), 2925 (s), 2871 (m), 2855 (m), 1777 (w), 1730 (w), 1549 (m), 1521 (m), 1460 (s), 1429 (s), 1381 (s), 1372 (s), 1329 (s), 1297 (s), 1269 (s), 1214 (m), 1194 (m), 1166 (m), 1143 (s), 1112 (m), 1060 (w), 1050 (w), 1027 (m), 1002 (w), 983 (w), 961 (m), 927 (w), 853 (s), 830 (w), 781 (s), 741 (w), 725 (w), 704 (w), 686 (m), 664 (s), 607 (w), 579 (w), 522 (w), 437 (w). HRMS found m/z: 773.31403 [M⁺Na]⁺, C₄₀H₅₆O₄B₂NaS₄ requires: 773.31398.

3,3′′′-Dihexyl-5,5′′′-bis(2,2′:6′,2′′-terpyridine-4′-yl)-2,2′:5′,2′′:5′′,2′′′-quaterthiophene Q27-H. 3,3′′′-Dihexyl-(2,2′:5′,2′′:5′′,2′′′-quaterthiophene-5,5′′′-diyl)-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolane) (0.58 g, 0.77 mmol), Brtpy (0.488 g, 1.56 mmol), K₂CO₃ (0.34 g, 2.46 mmol) and PEPPSI-IPr (36 mg) were placed in a Schlenk tube and vacuum–argon cycles were applied. Toluene (15 mL) and methanol (15 mL) were added through the septum and the reaction mixture was heated to 90 °C overnight. After cooling to room temperature the mixture was diluted with dichloromethane (30 mL) and washed with water (3 × 200 mL). The organic layer was dried with MgSO₄, filtered and evaporated to obtain the crude product. The product was purified by column chromatography (Al₂O₃, hexane/THF, 3 : 2). Orange powder (0.12 g, 17%). ¹H NMR (400 MHz, d-CDCl₃) δ ppm 8.78–8.76 (m, 4H, A⁶), 8.68 (s, 4H, B³), 8.65 (m, 4H, A³), 7.89 (td, J₁ = 7.7, J₂ = 1.7, 4H, A⁴), 7.66 (s, 2H, C⁴), 7.38 (ddd, J₁ = 7.5, J₂ = 4.7, J₃ = 1.3, 4H, A⁵), 7.21 (d, J = 3.9, 2H, D³ or D⁴), 7.17 (d, J = 3.9, D⁴ or D³), 2.87 (t, J = 3.9, 4H, Hex¹), 1.82–1.72 (m, 4H, Hex²), 1.50–1.36 (m, 12H, Hex³–Hex⁵), 0.97–0.89 (m, 4H, Hex⁶). ¹³C NMR (101 MHz, d-CDCl₃) δ ppm 156.05, 149.14, 142.96, 140.96, 139.17, 137.10, 136.87, 135.09, 132.42, 128.91, 126.85, 124.17, 123.92, 121.35, 116.59, 31.69, 30.57, 29.73, 29.73, 22.64, 14.13. IR (DRIFT), cm⁻¹ 3063 (m), 3013 (w), 2957 (m), 2925 (s), 2852 (m), 1974 (w), 1955 (w), 1724 (m), 1599 (s), 1583 (s), 1567 (s), 1544 (m), 1468 (s), 1458 (s), 1434 (m), 1403 (s), 1386 (m), 1361 (m), 1340 (w), 1298 (w), 1265 (m), 1254 (m), 1210 (m), 1195 (w), 1177 (w), 1146 (w), 1124 (m), 1093 (m), 1070 (m), 1037 (m), 1021 (m), 990 (m), 970 (w), 918 (w), 897 (w), 879 (m), 848 (m), 839 (m), 789 (s), 776 (s), 742 (s), 728 (m), 715 (w), 693 (w), 682 (m), 663 (m), 658 (m), 642 (m), 631 (m), 622 (m), 585 (w), 566 (w), 524 (w), 501 (m), 461 (w), 403 (m). HRMS found m/z: 961.32106 [M⁺H]⁺, C₅₈H₃₃N₆S₄ requires: 961.32090.

3,3′′′-Bis(6-(4-methoxyphenoxy)hexyl)-2,2′:5′,2′′:5′′,2′′′-quaterthiophene. 2-Bromo-3-(6-(4-methoxyphenoxy)hexyl)thiophene (3.5 g, 9.5 mmol), 5,5′-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-2,2′-bithiophene (1.4 g, 4.8 mmol), K₂CO₃ (3.94 g, 28.5 mmol), and PEPPSI-IPr (150 mg) were introduced into a pre-dried Schlenk tube with a magnetic stirring bar and vacuum–argon cycles were applied. A mixed solvent (toluene/methanol, 1 : 1) was added and the reaction mixture was heated at 90 °C for 24 hours. After cooling to room temperature the reaction mixture was extracted with dichloromethane, the organic phase was dried with MgSO₄, filtered off and evaporated. The crude product was purified by precipitation from concentrated THF solution by using hexane. Orange powder (3.4 g, 97%). ¹H NMR (400 MHz, d-CDCl₃) δ ppm 7.19 (d, J = 5.2, 2H, C⁴ or C⁵), 7.12 (d, J = 3.8, 2H, D³ or D⁴), 7.01 (d, J = 3.8, 2H, D⁴ or D³), 6.95 (d, J = 5.2, 2H, C⁵ or C⁴), 6.81–6.83 (m, 8H, –Ph), 3.90 (t, J = 6.6, 4H, Hex⁶), 3.76 (s, 6H, –OCH₃), 2.81 (t, J = 7.9, 4H, Hex¹), 1.65–1.81 (m, 8H, Hex² + Hex⁵), 1.41–1.51 (m, 8H, Hex³ + Hex⁴). ¹³C NMR (101 MHz, d-CDCl₃) δ ppm 160.43, 153.65, 153.24, 150.09, 144.13, 139.65, 135.24, 130.39, 126.60, 123.86, 115.41, 114.60, 69.10, 68.54, 30.53, 29.31, 29.18, 27.14, 25.87. IR (DRIFT), cm⁻¹ 3096 (m), 3070 (m), 3056 (m), 3042 (w), 3001 (m), 2937 (s), 2928 (s), 2855 (s), 2834 (m), 2067 (w), 1857 (w), 1750 (m), 1615 (w), 1591 (m), 1539 (w), 1508 (s), 1495 (m), 1467 (m), 1456 (m), 1442 (m), 1422 (m), 1389 (m), 1378 (w), 1347 (w), 1322 (m), 1308 (m), 1294 (m), 1231 (s), 1193 (s), 1176 (m), 1154 (w), 1146 (w), 1108 (m), 1090 (m), 1071 (s), 1056 (m), 1038 (s), 1005 (w), 989 (s), 958 (w), 940 (m), 929 (m), 919 (m), 906 (w), 889 (w), 876 (m), 855 (m), 826 (s), 805 (s), 792 (s), 757 (m), 742 (s), 722 (m), 699 (m), 687 (m), 669 (m), 654 (m), 638 (w), 631 (w), 599 (w), 586 (w), 566 (w), 521 (s), 506 (m), 472 (w), 462 (m), 426 (w). HRMS found m/z: 765.21732 [M⁺Na]⁺, C₄₂H₄₆O₄NaS₄ requires: 765.21711.

5,5′′′-(3,3′′′-Bis(6-(4-methoxyphenoxy)hexyl-2,2′:5′,2′′:5′′,2′′′-quaterthiophene-5,5′′′-diyl)bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolane). 3,3′′′-Bis(6-(4-methoxyphenoxy)hexyl)-2,2′:5′,2′′:5′′,2′′′-quaterthiophene (0.6 g, 0.8 mmol), dtbpy (9 mg, 0.03 mmol) and ([Ir(OMe)(COD)]₂) (9 mg, 0.01 mmol) were placed in a tube and vacuum–argon cycles were applied. Tetrahydrofuran (12 mL), hexane (12 mL) and HBpin (0.24 mL, 0.21 g, 2.1 mmol) were added. The tube was heated at 50 °C for 24 hours. After opening the tube, water was added and the mixture was stirred for an hour. Then the reaction mixture was extracted with dichloromethane, the organic phase was dried with MgSO₄, filtered off and evaporated to obtain the product (0.76 g, 95%). The product was used as obtained for the following synthesis without purification. ¹H NMR (400 MHz, d-CDCl₃) δ ppm 7.47 (s, 2H, C⁴), 7.13 (d, J = 3.9, 2H, D³ or D⁴), 7.07 (d, J = 3.9, 2H, D⁴ or D³), 6.82 (s, 8H, –Ph), 3.89 (t, J = 6.6, 4H, Hex⁶), 3.76 (s, 6H, –OCH₃), 2.81 (t, J = 7.4, 4H, Hex¹), 1.80–1.69 (m, 8H, Hex² + Hex⁵), 1.52–1.44 (m, 8H, Hex³ + Hex⁴), 1.36 (s, 24H, –CH₃pinacol ester). ¹³C NMR (101 MHz, d-CDCl₃) δ ppm 153.64, 153.25, 140.70, 140.09, 137.53, 137.07, 135.30, 126.85, 124.10, 115.41, 114.59, 84.18, 68.56, 55.71, 30.44, 29.29, 29.26, 29.12, 25.88, 24.75, 24.59. ¹¹B NMR (128.3 MHz, d-CDCl₃) δ ppm 22.50. IR (DRIFT), cm⁻¹ 3092 (w), 2975 (m), 2936 (m), 2861 (m), 2833 (w), 1752 (w), 1617 (w), 1593 (w), 1544 (w), 1508 (s), 1471 (m), 1456 (m), 1380 (m), 1372 (m), 1334 (m), 1306 (m), 1266 (m), 1231 (s), 1180 (m), 1167 (m), 1143 (m), 1107 (m), 1073 (m), 1039 (m), 1009 (m), 983 (m), 967 (w), 926 (w), 902 (w), 851 (m), 825 (m), 793 (m), 743 (m), 721 (m), 700 (m), 674 (m), 606 (w), 578 (w), 522 (m). HRMS found m/z: 1017.38703 [M⁺Na]⁺, C₅₄H₆₈O₈B₂NaS₄ requires: 1017.38753.

3,3′′′-Bis(6-(4-methoxyphenoxy)hexyl)-5,5′′′-bis(2,2′:6′,2′′-terpyridin-4′-yl)-2,2′:5′,2′′:5′′,2′′′-quaterthiophene Q27-A. Brtpy (0.33 g, 1.03 mmol), K₂CO₃ (0.20 g, 1.47 mmol) and PEPPSI-IPr (20 mg) were placed in a pre-dried Schlenk tube and three vacuum–argon cycles were applied. 5,5′′′-(3,3′′′-Bis(6-(4-methoxyphenoxy)hexyl-2,2′:5′,2′′:5′′,2′′′-quaterthiophene-5,5′′′-diyl)-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolane) (0.47 g, 0.47 mmol) was dissolved in toluene (15 mL) and added to the tube. Methanol (15 mL) was added and the reaction mixture was heated at 90 °C for 24 hours. After cooling to room temperature the mixture was extracted with dichloromethane, the organic phase was dried with MgSO₄, filtered off and evaporated. The crude product was purified by column chromatography (Al₂O₃, hexane/THF, 3 : 2) to obtain the product as an orange solid (0.18 g, 32%). ¹H NMR (400 MHz, d-CDCl₃) δ ppm 8.75–8.78 (m, 4H, A⁶), 8.68–8.65 (m, 8H, B³ + A³), 7.89 (td, J₁ = 8.0, J₂ = 1.8, 4H, A⁴), 7.66 (s, 2H, C⁴), 7.38 (ddd, J₁ = 7.6, J₂ = 4.9, J₂ = 1.5, 4H, A⁵), 7.19 (d, J = 3.8, 2H, D³ or D⁴), 7.14 (d, J = 4.10, 2H, D⁴ or D³), 6.79–6.86 (m, 8H, –Ph), 3.93 (t, J = 6.3, 4H, Hex⁶), 3.75 (s, 6H, –OCH₃), 2.88 (t, J = 7.9, 4H, Hex¹), 1.76–1.86 (m, 8H, Hex² + Hex⁵), 1.52–1.59 (m, 8H, Hex³ + Hex⁴). ¹³C NMR (101 MHz, d-CDCl₃) δ ppm 156.07, 156.03, 153.65, 153.27, 149.14, 142.91, 140.72, 139.27, 137.10, 136.86, 135.00, 132.48, 128.84, 126.93, 124.22, 123.92, 121.33, 116.53, 115.44, 114.59, 68.56, 55.72, 30.47, 29.57, 29.34, 29.32, 25.94. IR (DRIFT), cm⁻¹ 3060 (m), 3050 (m), 3011 (w), 2930 (s), 2858 (m), 1601 (s), 1584 (s), 1568 (s), 1545 (m), 1508 (s), 1466 (s), 1441 (m), 1401 (s), 1384 (w), 1334 (w), 1303 (w), 1289 (w), 1263 (m), 1231 (s), 1181 (m), 1146 (w), 1123 (m), 1105 (m), 1095 (m), 1071 (m), 1039 (m), 1019 (m), 990 (m), 882 (m), 831 (m), 823 (m), 787 (s), 774 (m), 740 (m), 726 (m), 706 (w), 670 (w), 660 (m), 630 (m), 622 (m), 567 (w), 525 (w), 498 (w), 468 (w), 425 (w), 400 (m). HRMS found m/z: 1205.39458 [M⁺H]⁺, C₇₂H₆₅O₄N₆S₄ requires: 1205.39446.

3,3′-Bis(6-(4-methoxyphenoxy)hexyl-2,2′-bithiophene. 2-Bromo-3-(6-(4-methoxyphenoxy)hexyl)thiophene (1.66 g, 4.5 mmol), B₂pin₂ (0.71 g, 2.8 mmol), K₂CO₃ (1.8 g, 13 mmol) and PEPPSI-IPr (112 mg) were placed in a Schlenk tube and vacuum–argon cycles were applied. Toluene (16 mL) and methanol (16 mL) were added and the reaction mixture was heated at 90 °C for 24 hours. After cooling to room temperature the reaction mixture was extracted with dichloromethane, the organic phase was dried with MgSO₄, filtered off and evaporated. The crude product was purified by column chromatography (SiO₂, hexane/CH₂Cl₂, 1 : 1) to obtain the pure product (0.62 g, 48%). ¹H NMR (300 MHz, d-CDCl₃) δ ppm 7.29 (d, J = 5.4, 2H, D⁴ or D⁵), 6.96 (d, J = 5.1, 2H, D⁵ or D⁴), 6.82 (s, 8H, –Ph), 3.84 (t, J = 6.5, 4H, Hex⁶), 3.77 (s, 6H, –OCH₃), 2.52 (t, J = 7.7, 4H, Hex¹), 1.74–1.67 (m, 4H, Hex⁵), 1.63–1.56 (m, 4H, Hex²), 1.44–1.29 (m, 8H, Hex³ + Hex⁴). ¹³C NMR (101 MHz, d-CDCl₃) δ ppm 153.32, 152.93, 141.80, 128.43, 128.19, 125.0, 115.08, 114.27, 68.21, 55.43, 30.29, 28.94, 28.77, 28.34, 25.49. IR (DRIFT), cm⁻¹ 3107 (m), 3064 (m), 3046 (m), 3011 (m), 2932 (s), 2854 (s), 2836 (m), 1510 (s), 1476 (m), 1466 (m), 1442 (m), 1395 (m), 1379 (w), 1349 (w), 1335 (w), 1291 (s), 1269 (m), 1239 (s), 1179 (m), 1154 (w), 1130 (w), 1109 (m), 1090 (m), 1073 (w), 1038 (s), 1016 (m), 1001 (m), 943 (w), 932 (m), 915 (m), 894 (m), 884 (m), 826 (s), 789 (w), 767 (w), 742 (s), 732 (m), 717 (s), 695 (m), 686 (m), 663 (m), 629 (m), 602 (w), 571 (w), 531 (m), 521 (m), 509 (m), 490 (w), 436 (w), 422 (w). HRMS found m/z: 579.25984 [M⁺H]⁺, C₃₄H₄₃O₄S₂ requires: 579.25973.

5,5′-(3,3′-Bis(6-(4-methoxyphenoxy)hexyl-2,2′-bithiophene-5,5′-diyl)bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolane). 3,3′-Bis(6-(4-methoxyphenoxy)hexyl-2,2′-bithiophene (0.6 g, 1.0 mmol), dtbpy (46 mg, 0.17 mmol) and ([Ir(OMe)(COD)]₂) (48 mg, 0.07 mmol) were placed in a tube and vacuum–argon cycles were applied. Tetrahydrofuran (15 mL), hexane (15 mL) and HBpin (0.6 mL, 0.53 g, 4.2 mmol) were added through septum. The tube was heated at 50 °C for 4 days. After opening the tube, water was added and the solution was stirred for an hour. Then the reaction mixture was extracted with dichloromethane, the organic phase was dried with MgSO₄, filtered off and evaporated to obtain the product (0.88 g, 100%). The product was used as obtained for the following synthesis without purification. ¹H NMR (300 MHz, d-CDCl₃) δ ppm 7.52 (s, 2H, D⁴), 6.82 (s, 8H, –Ph), 3.85 (t, J = 6.5, 4H, Hex⁶), 3.77 (s, 6H, –OCH₃), 2.53 (t, J = 7.7, 4H, Hex¹), 1.88–1.84 (m, 4H, Hex⁵), 1.72–1.68 (m, 4H, Hex²), 1.60–1.54 (m, 4H, Hex³), 1.42–1.30 (m, 28H, Hex⁴ + –CH₃ pinacol ester). ¹³C NMR (101 MHz, d-CDCl₃) δ ppm 153.59, 153.25, 143.42, 138.71, 136.29, 128.71, 115.41, 114.58, 84.10, 68.55, 55.74, 30.56, 29.24, 29.10, 28.57, 25.82, 24.76. ¹¹B NMR (128.3 MHz, d-CDCl₃) δ ppm 22.48. IR (DRIFT), cm⁻¹ 3045 (w), 2977 (s), 2934 (s), 2857 (s), 2833 (m), 1615 (w), 1591 (m), 1532 (m), 1508 (s), 1470 (m), 1456 (m), 1435 (m), 1380 (m), 1373 (m), 1329 (m), 1296 (m), 1268 (m), 1232 (s), 1180 (w), 1167 (w), 1142 (s), 1107 (m), 1074 (w), 1039 (m), 984 (w), 961 (m), 925 (w), 853 (m), 825 (m), 802 (m), 773 (w), 742 (m), 723 (m), 686 (m), 665 (s), 605 (w), 578 (m), 523 (m), 436 (w). HRMS found m/z: 853.41211 [M⁺Na]⁺, C₄₆H₆₄O₈B₂NaS₂ requires: 853.41209.

4′,3′′-Bis(6-(4-methoxyphenoxy)hexyl-5,5′′′-bis(2,2′:6′,2′′-terpyridine-4′-yl)-2,2′:5′,2′′:5′′,2′′′-quaterthiophene Q45-A. 4′-(5-Bromothiophene-2-yl)-2,2′:6′2′′-terpyridine (0.6 g, 1.62 mmol), K₂CO₃ (0.78 g, 5.6 mmol) and PEPPSI (54 mg) were placed in a Schlenk tube and vacuum–argon cycles were applied. 5,5′-(3,3′-Bis(6-(4-methoxyphenoxy)hexyl-2,2′-bithiophene-5,5′-diyl)bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolane) (0.68 g, 0.8 mmol) was dissolved in toluene (16 mL) and added to the tube. Methanol (16 mL) was added and the reaction mixture was heated at 95 °C for 20 hours. After cooling to room temperature the mixture was extracted with dichloromethane, and the organic phase was dried with MgSO₄, filtered off and evaporated. The crude product was purified by column chromatography (Al₂O₃, hexane/THF 3 : 2) to obtain the product as an orange solid (0.28 g, 28%). ¹H NMR (400 MHz, d-CDCl₃) δ ppm 8.77–8.75 (m, 4H, A⁶), 8.70 (s, 4H, B³), 8.67 (dt, J₁ = 8.0, J₂ = 1.1, 4H, A³), 7.89 (td, J₁ = 7.8, J₂ = 1.8, 4H, A⁴), 7.71 (d, J = 7.3, 2H, C⁴), 7.38 (ddd, J₁ = 7.4, J₂ = 4.8, J₃ = 1.4, 4H, A⁵), 7.24 (d, J = 3.6, 2H, C³), 7.19 (s, 2H, D⁴), 6.8 (s, 4H, –Ph), 6.79 (s, 4H, –Ph), 3.89 (t, J = 6.5, 4H, Hex⁶), 3.71 (s, 6H, –OMe), 2.61 (t, J = 7.6, 4H, Hex¹), 1.80–1.73 (m, 4H, Hex⁵), 1.70–1.64 (m, 4H, Hex²), 1.50–1.40 (m, 8H, Hex³ + Hex⁴). ¹³C NMR (101 MHz, d-CDCl₃) δ ppm 156.12, 155.99, 153.60, 153.26, 149.16, 143.53, 142.98, 140.34, 138.88, 136.86, 136.23, 127.99, 126.64, 125.88, 124.62, 123.92, 121.30, 116.66, 115.38, 114.57, 68.54, 55.66, 30.52, 29.28, 29.06, 28.89, 25.84. IR (DRIFT), cm⁻¹ 3064 (m), 3049 (m), 3004 (m), 2936 (s), 2859 (m), 2831 (w), 1599 (m), 1582 (s), 1566 (m), 1552 (m), 1507 (s), 1466 (s), 1446 (m), 1399 (m), 1382 (w), 1362 (w), 1303 (w), 1290 (w), 1265 (m), 1231 (s), 1181 (m), 1152 (w), 1146 (w), 1125 (w), 1107 (m), 1095 (m), 1085 (w), 1065 (m), 1038 (m), 1011 (m), 990 (m), 946 (w), 919 (w), 907 (w), 882 (m), 878 (m), 862 (w), 848 (w), 825 (s), 789 (s), 773 (m), 743 (m), 729 (m), 720 (m), 701 (w), 680 (m), 658 (m), 633 (m), 622 (m), 584 (w), 565 (w), 535 (w), 523 (m), 506 (w), 494 (w), 468 (w), 456 (w), 418 (w), 403 (m). HRMS found m/z: 1205.39479 [M⁺H]⁺, C₇₂H₆₅O₄N₆S₄ requires: 1205.39446.

3,4′,3′′,3′′′-Tetra(6-(4-methoxyphenoxy)hexyl)-2,2′:5′,2′′:5′′,2′′′-quaterthiophene. 5,5′-(3,3′-Bis(6-(4-methoxyphenoxy)hexyl-2,2′-bithiophene-5,5′-diyl)bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolane) (1.04 g, 1.25 mmol), 2-bromo-3-(6-(4-methoxyphenoxy)hexyl)thiophene (0.991 g, 2.68 mmol), K₂CO₃ (1.16 g, 8.4 mmol) and PEPPSI-IPr (94 mg) were placed in a Schlenk tube and vacuum–argon cycles were applied. Toluene (15 mL) and methanol (15 mL) were added through the septum and the reaction mixture was heated at 90 °C overnight. After cooling to room temperature the reaction mixture was diluted with dichloromethane (25 mL) and washed with water. The organic layer was dried with MgSO₄, filtered and evaporated. The crude product was purified by column chromatography (Al₂O₃, hexane/THF, 4 : 1) (0.42 g, 30%). ¹H NMR (400 MHz, d₂-CD₂Cl₂) δ ppm 7.18 (d, J = 5.1, 2H, E⁵), 7.02 (s, 2H, F³), 6.95 (d, J = 5.5, 2H, E⁴), 6.78 (s, 8H, –Ph), 6.76 (s, 8H, –Ph), 3.87–3.81 (m, 8H, Hex⁶), 3.72 (s, 12H, –OCH₃), 2.80 (t, J = 7.8, 4H, Hex¹), 2.59 (t, J = 7.8, 4H, Hex¹), 1.75–1.61 (m, 16H, Hex² + Hex⁵), 1.46–1.39 (m, 16H, Hex³ + Hex⁴). ¹³C NMR (101 MHz, d₂-CD₂Cl₂) δ ppm 154.25, 153.85, 143.37, 140.11, 136.57, 131.12, 130.77, 128.76, 128.00, 124.20, 115.82, 115.04, 69.04, 56.13, 32.16, 31.20, 29.84, 29.72, 26.44. IR (DRIFT), cm⁻¹ 3105 (w), 3074 (w), 3047 (w), 2997 (w), 2935 (s), 2858 (s), 1512 (s), 1466 (m), 1439 (w), 1389 (w), 1288 (m), 1242 (s), 1215 (s), 1180 (m), 1157 (w), 1111 (m), 1068 (m), 1041 (s), 987 (w), 941 (w), 922 (w), 825 (s), 741 (m), 721 (m), 687 (w), 652 (w), 525 (m). HRMS found m/z: 1155.49656 [M⁺H]⁺, C₆₈H₈₃O₈S₄ requires: 1155.49653.

5,5′′′-(3,4′,3′′,3′′′-Tetra(6-(4-methoxyphenoxy)hexyl)-2,2′:5′,2′′:5′′,2′′′-quaterthiophene-5,5′′′-diyl)bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolane). 3,4′,3′′,3′′′-Tetra(6-(4-methoxyphenoxy)hexyl)-2,2′:5′,2′′:5′′,2′′′-quaterthiophene (0.42 g, 0.36 mmol), dtbpy (13 mg) and ([Ir(OMe)(COD)]₂) (15 mg) were placed in a tube and vacuum–argon cycles were applied. Tetrahydrofuran (10 mL), hexane (10 mL) and HBpin (0.2 mL, 0.176 g, 1.38 mmol) were added and the reaction mixture was heated at 50 °C for 2 days. After opening the vessel the reaction mixture was diluted with water and stirred for an hour. Then the product was extracted with dichloromethane, dried with MgSO₄, filtered and evaporated. The product was used in the following synthesis without purification (0.48 g, 94%). ¹H NMR (400 MHz, d₂-CD₂Cl₂) δ ppm 7.43 (s, 2H, C⁴), 7.09 (s, 2H, D³), 6.78 (s, 8H, –Ph), 6.76 (s, 8H, –Ph), 3.87–3.81 (m, 8H, Hex⁶), 3.72 (s, 12H, –OCH₃), 2.81 (t, J = 8.0, 4H, Hex¹), 2.60 (t, J = 7.6, 4H, Hex¹), 1.75–1.60 (m, 16H, Hex² + Hex⁵), 1.48–1.40 (m, 16H, Hex³ + Hex⁴), 1.34 (s, 24H, –CH₃pinacol ester). ¹³C NMR (101 MHz, d₂-CD₂Cl₂) δ ppm 154.22, 153.86, 143.53, 141.23, 138.16, 136.51, 131.09, 129.23, 128.37, 115.83, 115.04, 84.74, 68.32, 56.13, 30.92, 29.89, 26.42, 26.15, 25.14, 24.93. ¹¹B NMR (128,3 MHz, d₂-CD₂Cl₂) δ ppm 22.39.

3,4′,3′′,3′′′-Tetra(6-(4-methoxyphenoxy)hexyl)-5,5′′′-bis(2,2′:6′,2′′-terpyridin-4′-yl)-2,2′:5′,2′′:5′′,2′′′-quaterthiophene Q2457-A. 5,5′′′-(3,4′,3′′,3′′′-Tetra(6-(4-methoxyphenoxy)hexyl)-2,2′:5′,2′′:5′′,2′′′-quaterthiophene-5,5′′′-diyl)bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolane) (0.45 g, 0.32 mmol), Brtpy (0.215 g, 0.69 mmol), K₂CO₃ (0.40 g, 2.89 mmol) and PEPPSI-IPr (32 mg) were placed in a Schlenk tube and vacuum and three vacuum–argon cycles were applied. The reaction mixture was heated to 90 °C overnight. After cooling to room temperature the mixture was diluted with dichloromethane (40 mL) and washed with water (3 × 200 mL). The organic layer was dried with MgSO₄, filtered and evaporated to obtain the crude product. The product was purified by column chromatography (Al₂O₃, hexane/THF, 3 : 2). Orange solid (0.17 g, 33%). ¹H NMR (400 MHz, d₂-CD₂Cl₂) δ ppm 8.74 (m, 4H, A⁶), 8.70 (s, 4H, B³), 8.67 (m, 4H, A³), 7.91 (td, J₁ = 7.7, J₂ = 2.1, 4H, A⁴), 7.67 (s, 2H, C⁴), 7.40–7.37 (m, 4H, A⁵), 7.19 (s, 2H, D⁴), 6.80–6.72 (m, 16H, –Ph), 3.90–3.83 (m, 8H, Hex⁶), 3.69 (s, 6H, –OCH₃), 3.66 (s, 6H, –OCH₃), 2.89 (t, J = 7.8, 4H, Hex¹), 2.66 (t, J = 7.8, 4H, Hex¹), 1.80–1.69 (m, 16H, Hex² + Hex⁵), 1.45–1.38 (m, 16H, Hex³ + Hex⁴). ¹³C NMR (101 MHz, d₂-CD₂Cl₂) δ ppm 156.71, 156.41, 154.23, 153.85, 149.74, 143.72, 143.37, 141.35, 139.47, 137.42, 136.23, 133.28, 129.58, 129.34, 128.46, 124.58, 121.62, 116.88, 115.83, 115.03, 69.06, 56.09, 31.06, 29.92, 29.70, 26.50, 26.42. IR (DRIFT), cm⁻¹ 3063 (w), 3009 (w), 2935 (s), 2854 (m), 1601 (m), 1581 (s), 1566 (s), 1508 (s), 1462 (s), 1400 (w), 1288 (w), 1238 (w), 1180 (w), 1149 (w), 1107 (m), 1072 (w), 1038 (s), 991 (w), 883 (w), 825 (m), 795 (m), 744 (m), 679 (w), 656 (m), 633 (w), 621 (w), 525 (w). HRMS found m/z: 1617.65658 [M⁺H]⁺, C₉₈H₁₀₁O₈N₆S₄ requires: 1617.65582.

General procedure for bromination of A-unimers

A unimer was dissolved in dichloromethane (to a concentration of ca. 0.02 M), the solution was then cooled in an ice bath and BBr₃ was added (excess). After 4 hours of stirring the cooling bath was removed and the solution was poured into water. The mixture was carefully neutralized with a saturated solution of K₂CO₃. Then the product was extracted with dichloromethane, dried with MgSO₄, filtered off and evaporated to obtain the desired product.

3,3′′′-Di(6-bromohexyl)-5,5′′′-bis(2,2′:6′,2′′-terpyridin-4′-yl)-2,2′:5′,2′′:5′′,2′′′-quaterthiophene Q27-Br. Red solid (90%). ¹H NMR (300 MHz, d-CDCl₃) δ ppm 8.75–8.79 (m, 4H, A⁶), 8.64–8.69 (m, 8H, A³ + B³), 7.89 (td, J₁ = 7.8, J₂ = 1.7, 4H, A⁴), 7.65 (s, 2H, C⁴), 7.38 (ddd, J₁ = 7.8, J₂ = 4.5, J₃ = 1.3, 4H, A⁵), 7.21 (d, J = 3.6, 2H, D³ or D⁴), 7.16 (d, J = 3.9, 2H, D⁴ or D³), 3.45 (t, J = 6.9, 4H, Hex⁶), 2.88 (t, J = 7.9, 4H, Hex¹), 1.99–1.73 (m, 12 H, Hex² + Hex⁴ + Hex⁵), 1.57–1.45 (m, 4 H, Hex³). ¹³C NMR (101 MHz, d-CDCl₃) δ ppm 155.97, 155.94, 149.08, 142.88, 140.52, 139.25, 137.08, 136.93, 134.97, 132.53, 128.82, 126.91, 124.22, 123.94, 121.37, 116.59, 33.92, 32.71, 30.32, 29.51, 28.69, 28.03. IR (DRIFT), cm⁻¹ 3063 (m), 3012 (w), 2931 (m), 2858 (m), 1601 (s), 1585 (s), 1566 (s), 1543 (m), 1466 (s), 1404 (s), 1385 (m), 1265 (w), 1122 (w), 1095 (w), 1072 (w), 1045 (w), 1018 (w), 991 (w), 883 (m), 845 (m), 791 (s), 741 (m), 660 (w), 621 (w). HRMS found m/z: 1117.14218 [M⁺H]⁺, C₅₈H₅₁N₆Br₂S₄ requires: 1117.14193.

4′,3′′-Di(6-bromohexyl-5,5′′′-bis(2,2′:6′,2′′-terpyridine-4′-yl)-2,2′:5′,2′′:5′′,2′′′-quaterthiophene Q45-Br. Orange solid (87%). ¹H NMR (400 MHz, d-CDCl₃) δ ppm 8.76 (dd, J₁ = 5.2, J₂ = 1.2, 4H, A³), 8.70 (s, 4H, B³), 8.67 (d, J = 7.9, 4H, A⁶), 7.89 (td, J₁ = 7.8, J₂ = 1.8, 4H, A⁴), 7.73 (d, J = 3.9, 2H, C⁴), 7.38 (m, 4H, A⁵), 7.17 (s, 2H, D⁴), 3.41 (t, J = 6.9, 4H, Hex⁶), 2.60 (t, J = 7.3, 4H, Hex¹), 1.72–1.61 (m, 8H, Hex² + Hex⁵), 1.49–1.36 (m, 8H, Hex³ + Hex⁴). ¹³C NMR (101 MHz, d-CDCl₃) δ ppm 156.11, 155.97, 149.14, 143.35, 142.97, 140.41, 138.80, 136.87, 127.96, 126.65, 125.81, 124.66, 123.94, 123.37, 121.32, 116.67, 33.91, 32.70, 30.44, 28.90, 28.49, 27.98. IR (DRIFT), cm⁻¹ 3063 (m), 3011 (m), 2932 (s), 2856 (m), 1775 (w), 1655 (w), 1599 (s), 1582 (s), 1567 (s), 1551 (s), 1509 (w), 1466 (s), 1438 (m), 1400 (s), 1378 (w), 1362 (m), 1301 (w), 1292 (w), 1266 (m), 1235 (m), 1182 (w), 1148 (w), 1126 (m), 1096 (m), 1065 (m), 1042 (m), 1011 (s), 989 (m), 903 (w), 877 (m), 860 (m), 848 (m), 825 (m), 791 (s), 772 (s), 745 (s), 732 (s), 680 (m), 659 (m), 633 (m), 622 (m), 584 (w), 564 (m), 537 (m), 497 (m), 468 (m), 452 (w), 439 (w), 404 (m). HRMS found m/z: 1117.14240 [M⁺H]⁺, C₅₈H₅₁N₆Br₂S₄ requires: 1117.14193.

3,4′,3′′,3′′′-Tetra(6-bromohexyl)-5,5′′′-bis(2,2′:6′,2′′-terpyridin-4′-yl)-2,2′:5′,2′′:5′′,2′′′-quaterthiophene Q2457-Br. Red solid (95%). ¹H NMR (400 MHz, d₂-CD₂Cl₂) δ ppm 8.74 (m, 4H, A⁶), 8.71 (s, 4H, B³), 8.68 (m, 4H, A³), 7.92 (td, J = 7.8, J = 7.8, J = 1.8, 4H, A⁴), 7.69 (s, 2H, C⁴), 7.40 (ddd, J = 7.8, J = 4.6, 4H, A⁵), 7.19 (s, 2H, D⁴), 3.46–3.41 (m, 8H, Hex⁶), 2.90 (m, 4H, Hex¹), 2.66 (m, 4H, Hex¹), 1.92–1.69 (m, 16H, Hex² + Hex⁵), 1.55–1.47 (m, 16H, Hex³ + Hex⁴). ¹³C NMR (101 MHz, d₂-CD₂Cl₂) δ ppm 156.29, 155.97, 149.32, 143.22, 142.97, 140.85, 139.19, 137.0, 135.89, 132.87, 129.14, 128.95, 128.06, 124.22, 121.29, 116.53, 34.32, 33.00, 30.55, 29.71, 28.75, 28.22. IR (DRIFT), cm⁻¹ 3062 (m), 3012 (m), 2930 (s), 2855 (s), 1731 (w), 1656 (w), 1598 (s), 1582 (s), 1567 (s), 1543 (m), 1466 (s), 1453 (s), 1437 (m), 1401 (s), 1382 (m), 1335 (w), 1278 (w), 1265 (m), 1236 (w), 1204 (w), 1192 (w), 1145 (w), 1124 (w), 1094 (m), 1071 (m), 1042 (m), 1014 (m), 990 (m), 971 (w), 936 (w), 883 (m), 865 (w), 847 (m), 837 (m), 820 (m), 791 (s), 773 (m), 743 (s), 730 (s), 712 (w), 676 (w), 660 (s), 633 (m), 622 (m), 564 (m), 540 (w), 500 (m), 467 (w), 403 (m). HRMS found m/z: 1441.15190 [M⁺H]⁺, C₇₀H₇₃N₆Br₄S₄ requires: 1441.15076.

General procedure for quaternization of Br-unimers

A unimer was dissolved in toluene (to a concentration of ca. 6.5 mM) and the flask was flushed with argon. Triethylphosphine (PEt₃) was added as 1 M solution in THF (ca. 20 eq.) and the reaction was heated to 110 °C for 4 days during which the quaternized product gets precipitated from the solution. After cooling to room temperature the product was filtered and washed with toluene and diethylether. The desired product was dried in vacuo.

6,6′-[5,5′′′-Bis(2,2′:6′,2′′-terpyridine-4′-yl)-(2,2′:5′,2′′:5′′,2′′′-quaterthiophen-3,3′′′-diyl)]-bis(hexan-1,1′-diyl triethylphosphonium) bromide Q27-P⁺. Dark red solid (74%). ¹H NMR (400 MHz, d₄-CD₃OD) δ ppm 8.60 (dd, J = 5.0, J = 1.4, 4H, A⁶), 8.44 (d, J = 7.9, 4H, A³), 8.29 (s, 4 H, B³), 7.89 (td, J₁ = 7.7, J₂ = 1.8, 4H, A⁴), 7.47 (s, 2H, C⁴), 7.39–7.45 (m, 4H, A⁵), 7.12 (d, J = 3.6, 2H, D³ or D⁴), 7.08 (d, J = 3.9, 2H, D⁴ or D³), 2.78–2.87 (m, 4H, Hex¹), 2.09–2.35 (m, 20H, P–CH₂ + Hex⁵ + Hex⁶), 1.69–1.83 (m, 8H, Hex² + Hex³), 1.10–1.34 (m, 22H, P–CH₃ + Hex⁴). Due to the low solubility of this compound we were not able to obtain the ¹³C NMR spectrum in a sufficient quality. ³¹P NMR (121.42 MHz, d₄-CD₃OD) δ ppm 38.93. IR (DRIFT), cm⁻¹ 3061 (m), 3012 (w), 2976 (m), 2933 (m), 2861 (m), 1599 (m), 1582 (s), 1567 (m), 1545 (m), 1535 (w), 1466 (m), 1454 (m), 1402 (m), 1387 (w), 1292 (w), 1267 (w), 1200 (w), 1146 (w), 1125 (m), 1096 (m), 1072 (m), 1048 (m), 1016 (m), 989 (m), 969 (w), 882 (m), 837 (w), 791 (s), 743 (s), 731 (m), 680 (m), 660 (s), 622 (m), 567 (m), 553 (m), 491 (m), 468 (m), 407 (m). HRMS found m/z: 597.23970 [M⁺H]²⁺, C₇₀H₈₀N₆P₂S₄z = 2 requires: 597.23958.

6,6′-[5,5′′′-Bis(2,2′:6′,2′′-terpyridine-4′-yl)-(2,2′:5′,2′′:5′′,2′′′-quaterthiophen-4′,3′′-diyl)]-bis(hexan-1,1′-diyl triethylphosphonium) bromide Q45-P⁺. Red solid (95%). ¹H NMR (400 MHz, d₄-CD₃OD) δ ppm 8.55–8.60 (m, 4H, A³), 8.43 (dd, J₁ = 7.9, J₂ = 1.1, 4H, A⁶), 8.33 (s, 4H, B³), 7.85–7.91 (m, 4H, A⁴), 7.55 (d, J = 3.8, 2H, C⁴), 7.39 (ddd, J₁ = 7.5, J₂ = 4.7, J₃ = 1.4, 4H, A⁵), 7.23 (s, 2H, D⁴), 7.13–7.16 (m, 2H, C³), 2.56–2.64 (m, 4H, Hex¹), 2.07–2.21 (m, 20H, P–CH₂ + Hex⁵ + Hex⁶), 1.60–1.72 (m, 8H, Hex² + Hex³), 1.07–1.20 (m, 22H, P–CH₃ + Hex⁴). ¹³C NMR (101 MHz, d₄-CD₃OD) δ ppm 156.81, 156.46, 149.98, 144.93, 144.07, 141.29, 140.29, 139.01, 138.11, 129.48, 128.51, 127.55, 126.29, 125.77, 122.94, 117.29, 31.88, 31.67, 30.26, 29.96, 22.47 (d, J = 4.4), 18.5 (d, J = 47.9), 12.44 (d, J = 49.4), 5.92 (d, J = 5.3). ³¹P NMR (121.42 MHz, d₄-CD₃OD) δ ppm 38.44. IR (DRIFT), cm⁻¹ 3062 (m), 3011 (m), 2975 (m), 2930 (s), 2858 (s), 1600 (s), 1583 (s), 1567 (s), 1551 (m), 1535 (m), 1466 (s), 1439 (m), 1400 (s), 1363 (w), 1324 (w), 1292 (w), 1267 (m), 1234 (m), 1179 (w), 1147 (w), 1125 (m), 1096 (m), 1062 (m), 1046 (m), 1011 (m), 990 (m), 969 (w), 880 (m), 861 (w), 847 (w), 791 (s), 773 (s), 742 (m), 726 (m), 682 (m), 660 (m), 623 (m), 580 (w), 539 (w), 497 (m), 470 (m), 463 (w), 405 (m). HRMS found m/z: 597.23959 [M⁺H]²⁺, C₇₀H₈₀N₆P₂S₄z = 2 requires: 597.23958.

6,6′,6′′,6′′′′-[5,5′′′-Bis(2,2′:6′,2′′-terpyridine-4′-yl)-(2,2′:5′,2′′:5′′,2′′′-quaterthiophen-3,4′,3′′,3′′′-tetrayl)]tetra(hexan-1,1′,1′′,1′′′-tetrayl triethylphosphonium) bromide Q2457-P⁺. Red solid (92%). ¹H NMR (400 MHz, d₄-CD₃OD) δ ppm 8.67–8.41 (m, 12H, A⁶ + A³ + B³), 7.99–7.90 (m, 4H, A⁴), 7.67 (s, 2H, C⁴), 7.49–7.43 (m, 4H, A⁵), 7.23 (s, 2H, D⁴), 2.90–2.84 (m, 4H, Hex¹), 2.70–2.84 (m, 4H, Hex¹), 2.31–2.15 (m, 40H, P–CH₂ + Hex⁵ + Hex⁶), 1.84–1.79 (m, 16H, Hex² + Hex³), 1.31–1.10 (m, 44H, P–CH₃ + Hex⁴). ¹³C NMR (101 MHz, d₄-CD₃OD) δ ppm 157.03, 156.58, 150.25, 144.59, 144.04, 142.02, 139.94, 138.92, 137.23, 134.15, 130.61, 129.97, 129.05, 125.69, 122.83, 117.39, 31.91, 31.31, 30.15, 22.55, 18.61 (d, J = 46.4), 13.94 (d, J = 50.8), 12.56 (d, J = 48.6), 6.03 (m). ³¹P NMR (161.92 MHz, d₄-CD₃OD) δ ppm 39.99. IR (DRIFT), cm⁻¹ 3444 (m), 3055 (w), 2978 (m), 2931 (s), 2854 (m), 1597 (m), 1581 (s), 1566 (m), 1466 (s), 1404 (m), 1269 (w), 1246 (w), 1200 (w), 1122 (w), 1095 (w), 1049 (m), 1018 (w), 991 (w), 887 (w), 845 (w), 795 (m), 744 (m), 660 (m), 621 (w), 509 (w), 471 (w), 455 (w). HRMS found m/z: 399.20815 [M⁺H]⁴⁺, C₉₄H₁₃₂N₆P₄S₄z = 4 requires: 399.20812.

Acknowledgements

This work was supported by the Czech Science Foundation (P108/12/1143), the Grant Agency of Charles University (project 64213) and the COST Action CM1302 (SIPS) European Network on Smart Inorganic Polymers.

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Footnote

† Electronic supplementary information (ESI) available. See DOI: 10.1039/c5dt04133c

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