Simultaneous enhancement of fluorescence and solubility by N-alkylation and functionalization of 2-(2-thienyl)imidazo[4,5-f][1,10]-phenanthroline with heterocyclic bridges

Abstract

A family of 2-(2-thienyl)imidazo[4,5-f][1,10]-phenanthroline (TIP) based compounds with large delocalized π systems has been designed and synthesized following the strategy of introducing alkyl chains and extending different S-, N- and O-containing aromatic heterocyclic tails. Simultaneous enhancements of the fluorescence emission and solubility in organic solvents for the resultant aromatic heterocyclic compounds 1–13 have been achieved. Analyses on twelve X-ray single-crystal structures indicate that the thiophene ring of the TIP unit in this series of compounds shows the same trans configuration with its imidazo[4,5-f][1,10]-phenanthroline core but different dihedral angles with the adjacent aromatic heterocycles. Thermal gravimetric analyses for ten imidazole N-substituted TIP derivatives reveal that they still retain good thermal stability with decomposition temperatures higher than 300 °C originating from their common TIP core, even with the introduction of the n-butyl radical in their molecular structure. Moreover, TPA and carbazole substituted compounds 2 and 9 were used as the ancillary ligands to prepare their corresponding ruthenium(II) sensitizers, BM3 and BM4, and their dye-sensitized solar cell performance was evaluated.

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1. Introduction

In recent years, research on organic luminescent materials has attracted great attention because of their importance in the application of light technology such as signaling, imaging and fluorescent biosensor/chemosensor materials.^1–5 In particular, materials bearing the “donor–acceptor” or “push–pull” structural architectures are more fascinating due to their efficient absorption of electromagnetic radiation by virtue of an intramolecular charge transfer and emission from their corresponding photoexcited state.^6–8 Consequently, considerable efforts have been conducted in designing and synthesizing diverse classes of the abovementioned fluorescent molecules.^9–14

Among the classes of organic π systems, nitrogen-containing heterocycles are very promising building blocks to synthesize a great number of strongly emissive materials.^15–18 1,10-Phenanthroline, as a type of common electron-deficient group, is often fused with electron-rich thiophene rings and bridged by imidazole groups. Therefore, a typical donor–acceptor molecule, i.e., 2-(2-thienyl)imidazo[4,5-f][1,10]-phenanthroline (TIP), was formed.¹⁹ Moreover, the two chelating coordinative sites of 1,10-phenanthroline are still reserved and makes it possible to fine-tune the optoelectronic properties over a wide range.^20–22 However, the fluorescence activity of TIP is not high enough and it is probably caused by its short conjugated π system.

In this work, the aim was to incorporate various aromatic units into the TIP backbone to extend the conjugated π system and the rigidity of resultant molecules, thereby manipulating their electronic structures and increasing their fluorescence emissions. Considering that the aromatic heterocyclic extension is limited by the solubility of resultant molecules, which will significantly reduce their reaction activity and make them very difficult to isolate and characterize, the alkylation strategy was used before the extension of the delocalized π system. So we report herein a family of TIP based compounds following the strategy of introducing alkyl chains and extending different S-, N- and O-containing aromatic heterocyclic tails from α position of the TIP thiophene ring, where simultaneous enhancements of fluorescence emission and solubility in organic solvents have been achieved. In addition, X-ray single-crystal structures of twelve compounds as well as thermal gravimetric analyses for ten imidazole N-substituted TIP derivatives have been explored. Moreover, TPA and carbazole substituted compounds 2 and 9 were used as the ancillary ligands to prepare their corresponding ruthenium(II) sensitizers, BM3 and BM4, and their dye-sensitized solar cell performance was evaluated.

2. Results and discussion

Syntheses

Generally, the Debus–Radziszewski reaction²³ between 1,10-phenanthroline-5,6-dione and a variety of formyl-thiophene derivatives in the presence of excess ammonium acetate is an effective way to construct TIP based aromatic heterocyclic compounds.^22,24–27 Herein the 2-(2-thienyl)imidazo[4,5-f][1,10]-phenanthroline (TIP) core was selected as the starting material for subsequent imidazole N-alkylation and aromatic heterocyclic extension because TIP based derivatives, including their metal complexes, have shown excellent optoelectronic properties and thermal stability. As shown in Scheme 1, our synthesis started from TIP based compounds 1 and 2, which were prepared using the Debus–Radziszewski reaction in high yield. Compared with TIP, 1 has two n-butyl chains in 3 and 4 positions of the thiophene ring and showed better solubility in common organic solvents. However, the two crowded n-butyl chains have large steric hindrance effects, which will generate large dihedral angles between the adjacent aromatic rings thereby influencing the extension of the delocalized π system to different extents.^28–31 Actually, mono-alkylation at the β position of the thiophene ring is an effective method for retaining the molecular planarity, but this strategy has the disadvantage of synthetic difficulties originating from molecular symmetry.

Scheme 1 Synthetic routes for TIP based heterocyclic aromatic fluorescent compounds.

As an alternative approach to increase the solubility and reaction activity of TIP based compounds, including easier purification and characterization of the final products, the following N-alkylation reactions to obtain compounds 3 and 4 were proceeded in the presence of NaH as a base in 73% and 74% yield, respectively. As expected, introduction of the mono-alkyl chain in compounds 3 and 4 results in an evident improvement of solubility in common organic solvents in comparison with TIP. In our experiments, two synthetic methods (methods A and B in Scheme 1) have been used to prepare 8, where the discrepancy between them is the sequence of the N-alkylation and Pd-catalyzed Suzuki–Miyaura cross-coupling reactions. Our results reveal that N-alkylation before cross-coupling (method B) has advantages of easy-handling and even higher yields mainly due to the increase in solubility and reaction activity. For example, in the case of compound 8, method B gave a higher two-step yield of 56% than method A (37%). Therefore, method B has been used to prepare other TIP based compounds (6–13). Consequently, all the TIP based target compounds 6–13 bearing pyridine-, ethyl benzoate-, triphenylamino-, phenylcarbazole-, thiophene-, formyl thiophene-, formyl furan- and dibenzothiophene-terminated substituents were prepared by Pd-catalyzed Suzuki–Miyaura cross-coupling reactions between intermediate 5 (obtained by the bromination from 4 using NBS in CH₂Cl₂ in a 91% yield) and a variety of boronic acids. All the reactions proceeded smoothly, which could be monitored directly by a UV-light detector excited at 365 nm with the color of fluorescence emission altering from light blue to deeper color. Furthermore, the molecular planarity of compounds 6–13 has been retained by our N-alkylation synthetic strategy, which could be verified by the following X-ray single-crystal structures with the dihedral angles between thiophene and its vicinal aromatic rings being less than 24.4(3)°.

Spectral characterization

The photophysical properties of the TIP based compounds 4–13 in CH₂Cl₂ at a concentration of 5.0 × 10⁻⁵ M were investigated and the spectral data are summarized in Table 2. Multiple absorption bands are observed in the UV-vis absorption spectra, as displayed in Fig. 1a. The wide peak located at 325–396 nm can be assigned as the π–π* transition absorption of the conjugated system. Evidently, TIPs 6–13 with the extension of aryl radicals to α position of the thiophene ring in the TIP unit exhibit not only a more red-shifted absorption, but also a considerably enlarged absorption area. Namely, when compared with the short conjugated length in 4 (325 nm and 24 800 L mol⁻¹ cm⁻¹), compounds 6–13 have larger λ_max (358–396 nm) and higher ε (28 100–46 900 L mol⁻¹ cm⁻¹) values. Moreover, it was also found that TIPs 6–13 show red-shifted absorptions to different extents with increase in the delocalized π system for all molecules after the aromatic heterocyclic extension.

Fig. 1 UV-vis absorption spectra (a) and fluorescence emission excited at 350 nm (b) for the TIP based compounds in their CH₂Cl₂ solutions at room temperature with the same concentration of 5.0 × 10⁻⁵ mol L⁻¹.

Similar to the absorption spectra, the fluorescence spectra of TIPs 6–13 also exhibit red-shifted emission bands in comparison with 4, and the photoluminescence capabilities also strengthened significantly. In our compounds, strong fluorescence signals were observed for compounds 6–9, whereas the fluorescence emission intensity of compounds 10–13 was considerably weaker. It is noted that compounds 6–9 have high Φ values of 70%, 69%, 73% and 72% (Table 1), whereas 5 is the weakest fluorescence emitter with a Φ value of 5.0% because of the fluorescence quenching effects of the bromine atom.^32,33 When compared with 10, having a Φ value of 38%, its structural analogue 11 bearing an additional formyl end group shows a higher Φ value of 46%. In addition, the replacement of thiophene with furan in 12 also leads to a distinct Φ value of 53%, which agrees well with the previously reported uridine monophosphate derivatives bearing a formyl-substituted thiophene or furan ring in position 5.³⁴

Table 1 UV-vis absorption and fluorescence emission data for compounds 4–13

Compd	UV-vis λmax [nm (eV)]	ε (L mol^−1 cm^−1)	Fluorescence		ΔλStokes^b (nm)	Td10^c (°C)
			λmax (nm)	Φs^a
a Photoluminescence quantum yields.b Stokes shift = λ^emmax − λ^absmax.c 10% weight-loss temperature.
4	325 (3.82)	24 800	423	0.11	98	435
5	328 (3.78)	26 200	416	0.05	88	374
6	358 (3.46)	28 100	448	0.70	90	435
7	364 (3.41)	36 900	459	0.69	95	412
8	386 (3.21)	46 900	480	0.73	94	435
9	359 (3.45)	34 200	462	0.72	103	470
10	362 (3.43)	32 100	451	0.38	89	392
11	396 (3.13)	33 900	508	0.46	112	403
12	380 (3.26)	40 300	470	0.53	90	361
13	359 (3.45)	35 400	449	0.37	90	463

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Single-crystal structures of TIP based compounds 3–13

When compared with the traditional means of characterization, X-ray single-crystal diffraction has evident advantages of characterizing the molecular geometry, crystal packing modes and supramolecular interactions. In this work, we have obtained single-crystal structures of eleven compounds, namely, 3·CHCl₃, 4, 6·H₂O, (7)₂·C₂H₅OH·(CHCl₃)₂, 8·CHCl₃, 9·CHCl₃, 10, 10·CHCl₃, 11·CHCl₃, 12, 13·CHCl₃ and intermediate 5·CHCl₃ (Fig. 2 and SI16†). These single crystal samples suitable for X-ray diffraction were grown by slow evaporation of their solution in CHCl₃ or in a mixture of CHCl₃ and EtOH.

Fig. 2 ORTEP diagrams (30% thermal probability ellipsoids) for the molecular structures of 6·H₂O, (7)₂·C₂H₅OH·(CHCl₃)₂, 8·CHCl₃, 9·CHCl₃, 10, 11·CHCl₃, 12 and 13·CHCl₃ showing the dihedral angle and relative configuration between adjacent aromatic heterocycles. All the solvent molecules are omitted for clarity.

In comparison with the conventional double β-alkylation of thiophene ring, our results reveal that the single imidazole N-alkylation strategy for TIP based compounds has the advantage of maintaining the planarity of the entire molecule in addition to significantly improving the solubility, which can be clearly verified by the small dihedral angles between the adjacent TIP rings in the twelve X-ray single-crystal structures. When compared with the dihedral angle between imidazo[4,5-f][1,10]phenanthroline and their neighbouring thiophene rings in the synthetic precursors 3·CHCl₃ and 4 (38.1(3)° and 38.2(2)°), the others target TIPs 6–13, which are terminated by various aryl groups at the α position of the thiophene ring in the TIP core, show smaller dihedral angles in the range of 4.6(4)°–24.4(3)°, indicating that the introduction of one n-butyl group in the imidazole ring does not destroy the planarity of the TIP based molecules too much. The observation of the discrepancy in the dihedral angle for compounds 6–13 before and after aromatic heterocyclic extension is consistent with the aforementioned fluorescence emission variations. In addition, the alkyl substituted nitrogen atom in the TIP unit and the neighbouring sulfur atom of the thiophene ring are found to point in opposite directions, exhibiting a common trans configuration. The crystal packing view of this family of TIPs is shown in Fig. SI17,† where typical intermolecular π–π stacking interactions are found between the adjacent aromatic rings.

Thermal stability

Thermal properties of all the powder samples of n-butyl containing TIP based compounds 4–13 have been further investigated by thermal gravimetric analysis (TGA) for comparison. As depicted in Fig. 3, all compounds, except 8, which may be impacted by the solvate CHCl₃, display excellent thermal stability with decomposition temperatures higher than 300 °C, and Td₁₀ values ranging from 374 to 463 °C. It is worth mentioning that the phenylcarbazole- and dibenzothiophene-terminated TIPs, 9 and 13, exhibit the best thermal stability. It is concluded that all the TIP derivatives bearing different terminating chromophores at the α position of the thiophene ring still retain good thermal stability even with the introduction of the n-butyl radical in the imidazole ring for better solubility and ease of purification.

Fig. 3 Thermograms of all n-butyl containing TIP based compounds (4–13).

Dye-sensitized solar cell performance of ruthenium(II) sensitizers containing TPA and carbazole substituted ancillary ligands

In recent years, ruthenium complexes containing 1,10-phenanthroline based ancillary ligands have been used in studies of dye-sensitized solar cells (DSCs).^35–38 In particular, TPA and carbazole involved ancillary ligands have shown good DSC performance^39–41 with high power-conversion efficiencies (PCEs). Therefore, in this work, TPA and carbazole substituted compounds 2 and 9 were used as the ancillary ligands to react with half molar ratio of [RuCl₂(p-cymene)]₂ and then with excess ammonium thiocyanate to produce corresponding ruthenium(II) sensitizers BM3 and BM4 (Scheme 2). In comparison with ligands 2 and 9, BM3 and BM4 display a new UV-vis absorption peak at 527 and 521 nm (Fig. 4a), respectively, indicative of typical metal-to-ligand charge transfer within the molecules.

Scheme 2 Synthetic route for two ruthenium sensitizers, BM3 and BM4.

Fig. 4 (a) UV-vis absorption spectra for 2, 9, BM3 and BM4 in DMF solutions. (b and c) Current density–voltage characteristics and IPCE spectra of the photovoltaic devices with different photosensitizers under illumination with AM1.5 simulated sunlight (100 mW cm⁻²) (thickness of TiO₂ = 12 μm; cell active area = 0.16 cm²).

The photocurrent density–voltage curves and incident photon-to-current efficiency (IPCE) spectra of BM3 and BM4 under the AM1.5 sunlight illumination are shown in Fig. 4b and c, respectively, together with our recently reported ruthenium(II) sensitizer BM1⁴² containing a carbazole terminated TIP ancillary ligand in the absence of an alkyl chain for comparison. It is noted that the BM4 based DSC has a relatively low PCE value of 4.62% compared to that of BM1 (Table 2) after the introduction of the n-butyl group on the imidazole nitrogen atom using the same cell fabrication and efficiency measuring procedures, which is consistent with the results of their IPCE spectra. In addition, the DSC fabricated from the TPA based ruthenium(II) sensitizer BM3 shows a considerably lower PCE value of 4.01% and an open-circuit voltage of 0.61 V. Our results indicate that the phenylcarbazole tail is better than the triphenylamino one in their PCEs of corresponding DSCs and the introduction of a long alkyl chain into the imidazole unit of the TIP based molecule cannot efficiently improve the overall DSC performance.

Table 2 Optical data and cell performance of the two ligands and three sensitizers

Sensitizer	λmax/nm^a	Jsc (mA cm^−2)	Voc (V)	FF^b	η^c (%)
	π–π*; π–π* or 4d–π*; 4d–π*
a Absorption maxima.b FF = fill factor.c The power conversion efficiency of N3-sensitized solar cell (where N3 is [Ru(dcbpy)2(NCS)2]) measured by the same device fabrication process is 6.07%.
2	293, 410
9	299, 359
BM1	301, 385, 525	16.50	0.69	64.1	7.34
BM3	299, 401, 527	9.45	0.61	69.2	4.01
BM4	299, 363, 521	9.93	0.69	67.4	4.62

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3. Conclusions

In summary, we have described herein a group of TIP based heterocyclic aromatic fluorescent compounds, including imidazole N-substituted alkyl chains (allyl and n-butyl). Synthetic, spectral, structural and thermal studies have been carried out to reveal the influence of N-alkylation and aromatic heterocyclic extension on the resulting TIP derivatives. It is concluded that a simultaneous enhancement of the fluorescence and solubility by N-alkylation and the following aromatic heterocyclic extension has been achieved for this series of heterocyclic aromatic compounds. In addition, good molecular planarity and thermal stability of the resultant aromatic heterocyclic extended TIPs can be retained by means of our synthetic strategy even with the introduction of an alkyl radical for better solubility and ease of purification, which can be verified by the small dihedral angles between the adjacent aromatic rings in nine X-ray single-crystal structures (<24.4(3)°) and the high decomposition temperatures (>300 °C). Furthermore, TPA and carbazole substituted compounds, 2 and 9, have been used as the ancillary ligands to prepare their corresponding ruthenium(II) sensitizers, BM3 and BM4, and their DSC performance was evaluated.

4. Experimental section

Materials and measurements

The synthetic details and characterization of 1,10-phenanthroline-5,6-dione,⁴³ 3,4-dibutylthiophene-2-carbaldehyde⁴⁴ and 2-triphenylamine-thiophene-5-carbaldehyde⁴⁵ have been previously reported. Unless otherwise specified, solvent of analytical grade was purchased from commercial sources and used as received. Column chromatography was carried out on silica gel (300–400 mesh). Standard techniques for synthesis were carried out under argon atmosphere. All melting points were measured without any corrections.

¹H and ¹³C NMR spectroscopic measurements were obtained with a Bruker AM-500 NMR spectrometer using TMS (SiMe₄) as an internal reference at room temperature. Electron ionization mass spectra (EI-MS, electron energy 70 eV) were recorded using a GCT TOF mass spectrometer (Micromass, Manchester, UK). Electrospray ionization mass spectra (ESI-MS) were recorded by a Thermo Fisher Scientific LCQ Fleet mass spectrometer over a scan range of 200–2000 amu. Electrospray ionization mass spectra (ESI-MS) were recorded by a Thermo Fisher Scientific LCQ Fleet mass spectrometer over a scan range of 100–2000 amu. Infrared (IR) spectra (4000–400 cm⁻¹) were recorded using a Nicolet FT-IR 170X spectrophotometer on KBr disks. UV-vis spectra were recorded with a Shimadzu UV-3150 double-beam spectrophotometer using a quartz glass cell with a path length of 10 mm. Elemental analyses (EA) for carbon, hydrogen and nitrogen were performed using a Perkin-Elmer 1400C analyzer. Luminescence spectra were recorded using an F-4600 fluorescence spectrophotometer at room temperature. Thermogravimetry analyses were carried out using a NETZSCH STA449C thermogravimetric analyzer under a nitrogen flow from 50 to 700 °C at a heating rate of 10.0 °C min⁻¹.

Luminescence spectra were recorded using a fluorescence spectrophotometer at room temperature (25 °C) using the same solutions as those used for the UV-vis determination. The fluorescence quantum yield gives the efficiency of the fluorescence process and the popular method to calculate it is to compare the fluorescence intensities (integrated areas) of a standard sample and the unknown one using the following equation. As can be seen in eqn (1), Φ_s is the luminescence quantum yield of the unknown sample, Φ_std is the luminescence quantum yield of the standard substance, I is the wavelength-integrated area of the corrected emission spectrum, and A is the absorbance value at the excitation wavelength. η_s and η_std represent the refractive indices of the corresponding solvents (pure solvents were assumed). We use anthracene in its ethanol solution as a standard sample (Φ_std = 27.0%, η_std = 1.36),⁴⁶ and TIP based compounds 4–13 were dissolved in CH₂Cl₂ (η_s = 1.42).

Photovoltaic measurements were recorded with a Newport Oriel solar simulator (Model 91160) equipped with a class a xenon light source powered by a Newport power supply. The power output of the lamp was measured to 1 Sun (100 mW cm⁻²) using a certified Si reference cell. The current–voltage (I–V) characteristics of each cell were obtained by applying an external potential bias to the cell and measuring the generated photocurrent with a Keithley digital source meter (Model 2400).

X-ray data collection and structural determination

Single-crystal samples of twelve compounds were covered with glue and mounted on glass fibers and then used for data collection. The crystal system was determined by Laue symmetry and the space groups were assigned on the basis of systematic absences using XPREP. Absorption correction was performed to the data and the structures were solved by direct methods and refined by a full-matrix least-squares method on F_obs² using the SHELXTL-PC software package.^47,48 All non-H atoms were anisotropically refined and all hydrogen atoms were inserted in the calculated positions assigned fixed isotropic thermal parameters and allowed to ride on their respective parent atoms. A summary of the crystal data, experimental details and refinement results for all twelve compounds is listed in Table 3, whereas selected bond distances and angles are given in Table SI1.†

Table 3 Crystal data and structural refinements for compounds 3–13^a

Compound	3·CHCl3	4	5·CHCl3	6·H2O	(7)2·EtOH(CHCl3)2	8·CHCl3
a R1 = Σ‖Fo| − |Fc‖/Σ|Fo|, wR2 = [Σ[w(Fo^2 − Fc^2)^2]/Σw(Fo^2)^2]^1/2.
Formula	C21H15N4SCl3	C21H18N4S	C22H18BrN4S2Cl3	C26H23N5SO	C64H60N8O5S2Cl6	C40H32N5SCl3
Molecular weight	461.78	358.45	556.72	453.55	1298.04	721.12
T [K]	291(2)	291(2)	291(2)	291(2)	291(2)	291(2)
Wavelength/Å	0.71073	0.71073	0.71073	0.71073	0.71073	0.71073
Crystal size (mm)	0.12 × 0.12 × 0.10	0.12 × 0.10 × 0.10	0.12 × 0.12 × 0.10	0.10 × 0.10 × 0.10	0.10 × 0.10 × 0.10	0.10 × 0.10 × 0.10
Crystal system	Triclinic	Triclinic	Triclinic	Monoclinic	Triclinic	Monoclinic
Space group	P1̄	P1̄	P1̄	P21/c	P1̄	P21/c
a [Å]	9.156(1)	9.713(2)	9.276(3)	16.294(2)	13.859(7)	21.993(2)
b [Å]	10.802(1)	9.923(2)	10.410(3)	7.769(1)	14.839(7)	9.058(1)
c [Å]	12.548(1)	11.205(2)	13.153(4)	19.272(2)	15.848(8)	19.520(2)
α [°]	72.798(1)	114.272(2)	107.382(5)	90	74.914(10)	90
β [°]	69.284(1)	109.020(3)	104.667(5)	116.931(6)	84.666(9)	112.815(1)
γ [°]	67.728(1)	97.147(3)	97.372(5)	90	87.572(10)	90
V [Å^3]	1055.3(10)	887.9(3)	1143.6(6)	2174.9(4)	3133(3)	3584.6(5)
Z/Dcalcd (g cm^−3)	2/1.453	2/1.341	2/1.617	4/1.385	2/1.376	4/1.336
F(000)	472	376	560	952	1348	1496
μ [mm^−1]	0.549	0.194	2.257	0.179	0.397	0.351
hmin/hmax	−6/10	−11/9	−8/11	−15/19	−16/16	−26/26
kmin/kmax	−12/12	−11/11	−12/11	−9/9	−16/17	−10/9
lmin/lmax	−11/14	−13/13	−15/15	−22/22	−17/18	−23/22
Data/parameter	3695/262	3088/236	3915/309	3833/299	10947/770	6317/442
Final R indices [I > 2σ(I)]	R1 = 0.0575, wR2 = 0.1502	R1 = 0.0432, wR2 = 0.1313	R1 = 0.0595, wR2 = 0.1526	R1 = 0.0522, wR2 = 0.1161	R1 = 0.0756, wR2 = 0.2019	R1 = 0.0706, wR2 = 0.1754
R indices (all data)	R1 = 0.0679, wR2 = 0.1568	R1 = 0.0503, wR2 = 0.1391	R1 = 0.0710, wR2 = 0.1579	R1 = 0.0890, wR2 = 0.1257	R1 = 0.1607, wR2 = 0.2283	R1 = 0.1288, wR2 = 0.1989
S	1.102	1.035	1.011	0.850	0.915	1.018
Max/min Δρ [e Å^−3]	0.775/−0.804	0.186/−0.380	0.846/−0.847	0.320/−0.395	0.649/−0.407	0.726/−0.614

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Compound	9·CHCl3	10	10·CHCl3	11·CHCl3	12	13·CHCl3
Formula	C40H30N5SCl3	C25H20N4S2	C26H21N4S2Cl3	C27H21N4OS2Cl3	C26H20N4O2S	C34H25N4S2Cl3
Molecular weight	719.10	440.57	559.94	587.95	452.52	660.05
T [K]	291(2)	291(2)	291(2)	291(2)	291(2)	291(2)
Wavelength/Å	0.71073	0.71073	0.71073	0.71073	0.71073	0.71073
Crystal size (mm)	0.12 × 0.12 × 0.08	0.10 × 0.08 × 0.08	0.12 × 0.10 × 0.10	0.10 × 0.10 × 0.10	0.10 × 0.10 × 0.10	0.13 × 0.13 × 0.10
Crystal system	Triclinic	Monoclinic	Triclinic	Monoclinic	Monoclinic	Monoclinic
Space group	P1̄	P21/c	P1̄	P21/c	P21/c	P21/c
a [Å]	12.404(2)	13.596(4)	9.339(1)	5.288(2)	13.767(2)	9.600(2)
b [Å]	12.454(2)	8.610(3)	12.161(2)	33.975(9)	8.367(1)	10.958(2)
c [Å]	13.762(2)	19.250(6)	12.848(2)	14.927(4)	19.124(3)	29.580(5)
α [°]	111.741(2)	90	71.990(3)	90	90	90
β [°]	100.880(3)	113.600(4)	85.936(3)	97.610(5)	108.372(2)	93.350(2)
γ [°]	110.123(2)	90	71.519(3)	90	90	90
V [Å^3]	1728.2(5)	2065.0(1)	1315.5(3)	2658.1(12)	2090.5(5)	3106.2(9)
Z/Dcalcd (g cm^−3)	2/1.382	4/1.417	2/1.414	4/1.469	4/1.438	4/1.411
F(000)	744	920	576	1208	944	1360
μ [mm^−1]	0.364	0.279	0.53	0.532	0.189	0.461
hmin/hmax	−14/14	−16/16	−8/11	−5/6	−16/16	−11/11
kmin/kmax	−14/14	−10/7	−14/14	−40/40	−9/6	−13/9
lmin/lmax	−13/16	−22/−22	−15/14	−17/10	−22/22	−35/35
Data/parameter	6017/471	3627/281	357/4612	4682/335	3654/299	5452/389
Final R indices [I > 2σ(I)]	R1 = 0.0478, wR2 = 0.1475	R1 = 0.0617, wR2 = 0.1551	R1 = 0.0680, wR2 = 0.1652	R1 = 0.0535, wR2 = 0.1192	R1 = 0.0876, wR2 = 0.2192	R1 = 0.0480, wR2 = 0.1208
R indices (all data)	R1 = 0.0764, wR2 = 0.1743	R1 = 0.1086, wR2 = 0.1749	R1 = 0.1232, wR2 = 0.1876	R1 = 0.1198, wR2 = 0.1393	R1 = 0.1260, wR2 = 0.2429	R1 = 0.0722, wR2 = 0.1309
S	1.090	0.961	1.004	0.972	1.060	1.058
Max/min Δρ [e·Å^−3]	0.272/−0.273	0.531/−0.465	0.415/−0.229	0.329/−0.282	1.358/−0.857	0.460/−0.410

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Syntheses and characterizations of compounds 1–13

Compound 1. 1,10-Phenanthroline-5,6-dione (1.00 g, 4.76 mmol), 3,4-dibutylthiophene-2-carbaldehyde (1.07 g, 4.77 mmol) and ammonium acetate (3.67 g, 47.61 mmol) were dissolved in 150 mL acetic acid. The mixture was heated to 100 °C for 10 h, cooled to room temperature, neutralized with 25% NH₃ solution and extracted with 200 mL CHCl₃. The organic layer was collected, dried over anhydrous Na₂SO₄ and concentrated in a vacuum. Compound 1 was finally separated by silica gel column chromatography using CHCl₃ as the eluent to give a light yellow solid in a yield of 1.52 g (77%). Mp: 184–186 °C. Main FT-IR absorptions (KBr pellets, cm⁻¹): 3420 (vs), 2957 (m), 2922 (m), 2854 (w), 1643 (m), 1564 (m), 1497 (m), 1433 (m), 1401 (m), 1347 (m), 1190 (w), 1071 (w), 1034 (w), 808 (m), 739 (s). ¹H NMR (500 MHz, CDCl₃) δ: 8.96 (m, 4H, phen), 7.58 (m, 2H, phen), 6.86 (s, 1H thiophene), 3.07 (m, 2H, n-butyl), 2.49 (m, 2H, n-butyl), 1.59 (m, 4H, n-butyl), 1.41 (m, 4H, n-butyl), 0.93 (m, 6H, n-butyl). ¹³C NMR (125 MHz, CDCl₃) δ: 147.5, 147.3, 144.0, 143.6, 142.8, 131.0, 126.0, 123.2, 121.3, 32.4, 31.8, 28.6, 7.5, 23.0, 22.5, 13.9. EI-TOF-MS (m/z): calcd for [C₂₅H₂₆N₄S]⁺ 414.2 (100.0%), found 414.2 (68.5%). Anal. calcd for C₂₅H₂₆N₄S: C, 72.43%; H, 6.32%; N, 13.51%. Found: C, 72.17%; H, 6.11%; N%, 13.24%.

Compound 2. 1,10-Phenanthroline-5,6-dione (1.00 g, 4.76 mmol), 2-triphenylamine-thiophene-5-carbaldehyde (1.60 g, 4.77 mmol) and ammonium acetate (3.67 g, 47.61 mmol) were dissolved in 200 mL acetic acid. The mixture was heated to 100 °C for 4 h, cooled to room temperature, transferred to an ice bath and neutralized with ammonia until no more precipitate was formed. The precipitate was filtered under reduced pressure, washed with excess water and anhydrous ether, and dried in vacuo to give 2 as a yellow solid in a yield of 2.05 g (79%). Mp: >300 °C. Main FT-IR absorptions (KBr pellets, cm⁻¹): 3467 (vs), 1688 (m), 1522 (m), 1189 (w), 631 (m). ¹H NMR (500 MHz, DMSO-d₆) δ: 13.86 (s, 1H, imidazole), 9.04 (s, 2H, phen), 8.86 (m, 2H, phen), 7.88–7.80 (m, 2H; phen + 1H, thiophene), 7.70 (d, 2H, J = 8.2 Hz, triphenylamine), 7.57 (d, 1H, J = 3.4 Hz, thiophene), 7.36 (m, 4H, triphenylamine), 7.11 (m, 6H, triphenylamine), 7.03 (d, 2H, J = 8.2 Hz, triphenylamine). ¹³C NMR (125 MHz, DMSO-d₆) δ: 148.2, 147.7, 147.1, 146.6, 145.3, 143.9, 131.9, 130.1, 129.9, 127.7, 127.3, 127.0, 124.9, 124.0, 123.7, 123.1. EI-TOF-MS (m/z): calcd for [C₃₅H₂₃N₅S]⁺ 545.2 (100.0%), found 545.1 (100.0%). Anal. calcd for C₃₅H₂₃N₅S: C, 77.04%; H, 4.25%; N, 12.83%. Found: C, 76.91%; H, 4.43%; N, 12.58%.

Compound 3. To a DMF (100 mL) solution of TIP (1.00 g, 3.31 mmol), NaH (0.24 g, 10.00 mmol) and allyl bromide (2.00 g, 16.55 mmol) were added. The resulting solution was stirred for 0.5 h at room temperature and heated to 105 °C for 12 h under an argon atmosphere. The reaction mixture was then cooled to room temperature and quenched with distilled water. The solvent was removed under reduced pressure, and then, the residue was dissolved in 200 mL CHCl₃ and rinsed with distilled water three times. The organic layer was collected, dried over anhydrous Na₂SO₄ and concentrated in a vacuum. The desired compound 3 was finally separated by silica gel column chromatography using CHCl₃ as the eluent to give a light yellow solid in a yield of 0.83 g (73%). Light yellow single crystals of 3, suitable for X-ray diffraction measurements, were obtained from CHCl₃ by slow evaporation in air at room temperature for 4 days. Mp: 196–198 °C. Main FT-IR absorptions (KBr pellets, cm⁻¹): 3016 (m), 2956 (m), 2868 (m), 1598 (w), 1564 (m), 1469 (s), 1394 (m), 1355 (m), 1155 (m), 1083 (m), 798 (m), 740 (s), 711 (m). ¹H NMR (500 MHz, CDCl₃) δ: 9.19 (dd, 1H, J = 3.4, 1.2 Hz, phen), 9.16 (d, 1H, J = 3.4 Hz, phen), 9.10 (dd, 1H, J = 6.5, 1.1 Hz, phen), 8.55 (d, 1H, J = 6.7 Hz, phen), 7.73 (m, 1H, phen), 7.64 (m, 1H, phen), 7.58 (d, 1H, J = 4.0 Hz, thiophene), 7.55 (d, 1H, J = 2.8 Hz, thiophene), 7.21 (m, 1H, thiophene), 6.38 (m, 1H, thiophene), 5.53 (d, 1H, J = 8.6 Hz, allyl), 5.34 (d, 2H, J = 1.8 Hz, allyl), 5.20 (d, 1H, J = 13.8 Hz, allyl). ¹³C NMR (125 MHz, CDCl₃) δ: 148.9, 147.7, 144.6, 144.1, 136.4, 132.0, 131.3, 130.5, 128.8, 128.3, 127.9, 127.8, 125.8, 123.8, 123.4, 122.4, 119.3, 118.3, 49.3. ESI-MS (m/z): calcd for [C₂₀H₁₄N₄S]⁺ 342.1 (100.0%), found: [M + 1]⁺ 343.3 (100.0%). Anal. calcd for C₂₀H₁₄N₄S: C, 70.15%; H, 4.12%; N, 16.36%. Found: C, 70.01%; H, 4.23%; N, 16.17%.

Compound 4. The synthetic procedure for 3 was followed using TIP (4.00 g, 13.24 mmol), NaH (0.96 g, 40.00 mmol), 1-bromobutane (9.08 g, 66.26 mmol) and DMF (250 mL). Compound 4 was obtained as a light yellow solid in a yield of 3.52 g (74%). Light yellow single crystals of 4 suitable for X-ray diffraction measurements were obtained from CHCl₃ by slow evaporation in air at room temperature for 1 day. Mp: 174–176 °C. Main FT-IR absorptions (KBr pellets, cm⁻¹): 3022 (m), 2960 (w), 2869 (w), 1595 (w), 1562 (m), 1514 (w), 1465 (s), 1396 (m), 1355 (m), 1155 (m), 1083 (m), 974 (w), 941 (w), 848 (w), 796 (s), 738 (s), 711 (s), 615 (w). ¹H NMR (500 MHz, CDCl₃) δ: 9.18 (m, 2H, phen), 9.08 (dd, 1H, J = 10.2, 2.2 Hz, phen), 8.57 (dd, 1H, J = 10.5, 1.8 Hz, phen), 7.71 (m, 2H, phen), 7.60 (dd, 1H, J = 5.1, 1.0 Hz, thiophene), 7.56 (dd, 1H, J = 3.6, 1.0 Hz, thiophene), 7.25 (dd, 1H, J = 5.1, 3.6 Hz, thiophene), 4.72 (m, 2H, n-butyl), 2.05 (m, 2H, n-butyl), 1.49 (m, 2H, n-butyl), 1.00 (m, 3H, n-butyl). ¹³C NMR (125 MHz, CDCl₃) δ: 148.9, 147.6, 147.2, 144.7, 144.1, 136.6, 131.5, 130.5, 128.6, 128.6, 127.8, 125.1, 123.9, 123.4, 122.6, 119.8, 46.7, 32.2, 19.7, 13.6. EI-TOF-MS (m/z): calcd for [C₂₁H₁₈N₄S]⁺ 358.1 (100.0%), found 358.2 (100.0%). Anal. calcd for C₂₁H₁₈N₄S: Anal. calcd for C₄₆H₃₂N₄S₃: C, 70.36%; H, 5.06%; N, 15.63%. Found: C, 70.19%; H, 5.11%; N, 15.43%.

Compound 8. The synthetic procedure for 3 was followed using 2 (0.50 g, 0.92 mmol), NaH (0.07 g, 2.92 mmol), 1-bromobutane (0.63 g, 4.60 mmol) and DMF (100 mL). Compound 8 was obtained as a yellowish green solid in a yield of 0.33 g (59%). Yellow single crystals of compound 8 suitable for X-ray diffraction determination were grown from a solution of CHCl₃ by slow evaporation in air at room temperature for 3 days. Mp: 223–225 °C. Main FT-IR absorptions (KBr pellets, cm⁻¹): 3030 (w), 2964 (w), 2931 (w), 2873 (w), 1589 (s), 1485 (s), 1396 (w), 1323 (m), 1282 (s), 1172 (w), 1080 (w), 804 (m), 746 (m), 698 (m), 621 (w). ¹H NMR (500 MHz, CDCl₃) δ: 9.16 (m, 2H, phen), 9.08 (d, 1H, phen), 8.57 (m, 2H, phen), 7.71 (m, 2H, phen), 7.56 (d, 2H, J = 8.5 Hz, triphenylamine), 7.49 (d, 1H, J = 3.8 Hz, thiophene), 7.33 (d, 1H, J = 3.8 Hz, thiophene), 7.30 (m, 4H, triphenylamine), 7.16 (m, 4H, triphenylamine), 7.12 (d, 2H, J = 8.6 Hz, triphenylamine), 7.07 (m, 2H, triphenylamine), 4.77 (m, 2H, n-butyl), 2.07 (m, 2H, n-butyl), 1.54 (m, 2H, n-butyl), 1.02 (m, 3H, n-butyl). ¹³C NMR (125 MHz, CDCl₃) δ: 149.0, 148.1, 147.6, 147.5, 147.4, 147.3, 144.7, 144.1, 136.8, 135.4, 130.6, 129.4, 129.2, 127.9, 127.9, 126.8, 125.3, 124.8, 124.7, 123.9, 123.5, 123.5, 123.2, 123.0, 122.7, 122.6, 122.3, 119.9, 46.9, 32.3, 19.8, 13.7. EI-TOF-MS (m/z): calcd for [C₃₉H₃₁N₅S]⁺ 601.2 (100.0%), found 601.4 (100.0%). Anal. calcd for C₃₉H₃₁N₅S: C, 77.84; H, 5.19; N, 11.64%. Found: C, 77.65; H, 5.14; N, 11.44%.

Compound 5. In the absence of light, NBS (1.52 g, 8.54 mmol) was dissolved in CH₂Cl₂ (10 mL) and injected into a solution of compound 4 (3.00 g, 8.38 mmol) in CH₂Cl₂ (20 mL) under an argon atmosphere. The mixture was refluxed for 5 h, and the resulting slurry was cooled to 0 °C and filtered. The solid was rinsed with distilled water, recrystallized from CHCl₃–hexane, and dried in a vacuum to give pure compound 5 as a light yellow solid (3.34 g, 91%). Light yellow single crystals of 5 suitable for X-ray diffraction measurements were obtained from CHCl₃ by slow evaporation in air at room temperature for 2 days. Main FT-IR absorptions (KBr pellets, cm⁻¹): 3039 (m), 2956 (m), 2927 (w), 2875 (w), 1604 (w), 1566 (w), 1471 (s), 1392 (m), 1352 (m), 1153 (m), 1083 (m), 1035 (w), 941 (w), 804 (s), 736 (s), 707 (m), 621 (w). Mp: >300 °C. ¹H NMR (500 MHz, CDCl₃) δ: 9.14 (m, 2H, phen), 9.00 (d, J = 8.1 Hz, phen), 8.50 (d, J = 8.3 Hz, phen), 7.68 (m, 2H, phen), 7.25 (d, 1H, J = 3.8 Hz, thiophene), 7.18 (d, 1H, J = 3.8 Hz, thiophene), 4.64 (m, 2H, n-butyl), 2.00 (m, 2H, n-butyl), 1.49 (m, 2H, n-butyl), 1.00 (m, 3H, n-butyl). ¹³C NMR (125 MHz, CDCl₃) δ: 149.0, 147.4, 145.8, 144.9, 144.3, 136.6, 133.3, 130.7, 130.3, 128.2, 127.7, 125.2, 123.7, 125.2, 123.7, 123.5, 122.5, 119.6, 115.7, 46.7, 32.0, 19.7, 13.6. EI-TOF-MS (m/z): calcd for [C₂₁H₁₇BrN₄S]⁺ 438.0 (100.0%), 436.0 (98.2%), found: 438.1 (88.0%), 436.1 (100.0%). Anal. calcd for C₂₁H₁₇BrN₄S: C, 57.67%; H, 3.92%; N, 12.81%. Found: C, 57.49%; H, 3.96%; N, 12.55%.

General procedure for the syntheses of compounds 6–13 from 5 via a Suzuki–Miyaura cross coupling reaction

A mixture of 5 (0.40 g, 0.92 mmol), boronic acid (1.00 mmol), Pd(PPh₃)₄ (0.12 g, 0.10 mmol) and Cs₂CO₃ (1.10 g, 2.76 mmol) was dissolved in a degassed mixture of dioxane (50 mL) and H₂O (5 mL), placed into a degassed three-necked flask and refluxed under an argon atmosphere for 10 h. After being cooled to room temperature, the solution was added into 100 mL CHCl₃, the organic layer washed with water, dried over anhydrous Na₂SO₄, and concentrated in a vacuum. The desired compounds 6–13 were finally separated by silica gel column chromatography using CHCl₃ as the eluent to give corresponding target products as a range of light yellow solid in 25–91% yield.

Compound 6. Pale yellow powder in a yield of 0.31 g (78%). Yellow single crystals of 6 suitable for X-ray diffraction determination were grown from a solution of CHCl₃/CH₃OH by slow evaporation in air at room temperature for 6 days. Mp: >300 °C. Main FT-IR absorptions (KBr pellets, cm⁻¹): 3037 (m), 2956 (m), 2931 (w), 2873 (w), 1598 (w), 1560 (w), 1471 (s), 1390 (m), 1357 (m), 1213 (w), 1153 (m), 1080 (m), 1035 (w), 941 (w), 804 (s), 736 (s), 707 (m), 615 (w). ¹H NMR (500 MHz, CDCl₃) δ: 9.16 (s, 2H, phen), 9.05 (d, 1H, J = 8.0 Hz, phen), 8.67 (d, 2H, J = 4.5 Hz, pyridine), 8.53 (d, 1H, J = 8.3 Hz, phen), 7.70 (m, 2H, phen), 7.59 (s, 1H, thiophene), 7.55 (d, 2H, J = 4.5 Hz, pyridine), 7.52 (s, 1H, thiophene), 4.74 (m, 2H, n-butyl), 2.10 (m, 2H, n-butyl), 1.51 (m, 2H, n-butyl), 1.01 (m, 3H, n-butyl). ¹³C NMR (125 MHz, CDCl₃) δ: 150.6, 149.2, 147.9, 146.4, 145.0, 144.3, 143.7, 140.5, 136.9, 133.3, 130.4, 128.9, 127.8, 125.8, 125.5, 123.8, 123.5, 119.8, 119.7, 46.9, 32.2, 19.8, 13.6. EI-TOF-MS (m/z): calcd for [C₂₆H₂₁N₅S]⁺ 435.2 (100.0%), found 435.3 (100.0%). Anal. calcd for C₂₆H₂₁N₅S: C, 71.70%; H, 4.86%; N, 16.08%. Found C, 71.56%; H, 4.91%; N, 15.88%.

Compound 7. Pale yellow powder in a yield of 0.37 g (79%). Yellow single crystals of 7 suitable for X-ray diffraction determination were grown from a mixture solution of CHCl₃/EtOH by slow evaporation in air at room temperature for 5 days. Mp: 241–243 °C. Main FT-IR absorptions (KBr pellets, cm⁻¹): 2927 (m), 1722 (s), 1641 (m), 1604 (m), 1560 (w), 1515 (w), 1456 (w), 1398 (m), 1267 (s), 1174 (w), 1107 (m), 1049 (w), 806 (m), 765 (m), 738 (m), 707 (w). ¹H NMR (500 MHz, CDCl₃) δ: 9.16 (m, 2H, phen), 9.06 (d, 1H, J = 8.1 Hz, phen), 8.54 (d, 1H, J = 8.3 Hz, phen), 8.11 (d, 2H, J = 8.1 Hz, phenyl), 7.75 (d, 2H, J = 8.1 Hz, phenyl), 7.70 (m, 2H, phen), 7.50 (s, 2H, thiophene), 4.75 (t, 2H, n-butyl), 4.42 (m, 2H, ethyl), 2.06 (m, 2H, n-butyl), 1.53 (m, 2H, n-butyl), 1.42 (t, 3H, ethyl), 1.02 (t, 3H, n-butyl). ¹³C NMR (125 MHz, CDCl₃) δ: 166.1, 149.1, 147.8, 145.8, 144.9, 144.3, 137.5, 136.9, 132.2, 130.4, 130.4, 129.9, 129.0, 127.8, 125.6, 125.4, 124.9, 123.8, 123.5, 122.6, 119.7, 61.1, 46.9, 32.2, 19.8, 14.3, 13.6. EI-TOF-MS (m/z): calcd for [C₃₀H₂₆N₄O₂S]⁺ 506.2 (100.0%), found 506.3 (100.0%). Anal. calcd for C₃₀H₂₆N₄O₂S: C, 71.12%; H, 5.17%; N, 11.08%. Found: C, 70.93%; H, 5.20%; N, 10.97%.

Compound 8. Yellowish green powder in a yield of 0.50 g (90%).

Compound 9. Yellowish green powder in a yield of 0.50 g (91%). Yellow single crystals of compound 9 suitable for X-ray diffraction determination were grown from a solution of CHCl₃ by slow evaporation in air at room temperature for 1 day. Mp: 238–240 °C. Main FT-IR absorptions (KBr pellets, cm⁻¹): 3060 (w), 2927 (m), 2873 (w), 1595 (m), 1500 (m), 1456 (s), 1361 (m), 1234 (m), 1083 (w), 798 (m), 744 (s), 702 (m), 657 (w). ¹H NMR (500 MHz, CDCl₃) δ: 9.21 (m, 2H), 9.13 (d, 1H, J = 8.1 Hz), 8.60 (d, 1H, J = 8.1 Hz), 8.48 (s, 1H), 8.24 (d, 1H, J = 7.7 Hz), 7.78–7.71 (m, 3H), 7.66 (m, 2H), 7.61 (d, J = 7.8 Hz), 7.55–7.22 (m, 2H), 7.49–7.44 (m, 4H), 7.36 (m, 1H), 4.83 (m, 2H), 2.13 (m, 2H), 1.58 (m, 2H), 1.07 (m, 3H). ¹³C NMR (125 MHz, CDCl₃) δ: 149.0, 148.8, 147.6, 147.5, 144.8, 144.2, 141.5, 140.8, 137.4, 136.9, 130.6, 130.0, 129.6, 129.1, 127.7, 127.0, 126.5, 125.8, 125.3, 124.4, 124.0, 123.4, 123.2, 122.7, 122.6, 120.5, 120.4, 119.9, 117.9, 110.3, 110.1, 46.9, 32.3, 19.8, 13.7. EI-TOF-MS (m/z): calcd for [C₃₉H₂₉N₅S]⁺ 599.2 (100.0%), found 599.4 (100.0%). Anal. calcd for C₃₉H₃₁N₅S: C, 78.10%; H, 4.87%; N, 11.68%. Found: C, 77.92%; H, 4.90%; N, 11.47%.

Compound 10. Pale yellow powder in a yield of 0.30 g (74%). Yellow single crystals of compound 10 suitable for X-ray diffraction determination were grown from the CHCl₃ solution by slow evaporation in air at room temperature for 3 days. Mp: >300 °C. Main FT-IR absorptions (KBr pellets, cm⁻¹): 3026 (w), 2958 (m), 2952 (w), 2873 (w), 1600 (w), 1560 (m), 1514 (m), 1479 (s), 1456 (m), 1421 (m), 1388 (m), 1155 (w), 1082 (m), 840 (m), 800 (s), 736 (s), 692 (s), 621 (w). ¹H NMR (500 MHz, CDCl₃) δ: 9.16 (m, 2H, phen), 9.06 (d, 1H, J = 8.0 Hz, phen), 8.55 (d, 1H, J = 8.4 Hz, phen), 7.70 (m, 2H, phen) 7.43 (d, 1H, J = 3.8 Hz, thiophene), 7.31 (d, 2H, J = 4.6 Hz, thiophene), 7.28 (d, 1H, J = 3.8 Hz, thiophene), 7.08 (m, 1H, thiophene), 4.75 (m, 2H, n-butyl), 2.06 (m, 2H, n-butyl), 1.53 (m, 2H, n-butyl), 1.02 (m, 3H, n-butyl). ¹³C NMR (125 MHz, CDCl₃) δ: 148.9, 147.6, 146.7, 144.6, 144.0, 140.3, 136.6, 136.3, 130.4, 130.1, 128.4, 127.7, 125.4, 125.3, 124.6, 124.0, 123.7, 123.4, 122.5, 119.6, 46.7, 32.1, 19.7, 13.6. EI-TOF-MS (m/z): calcd for [C₂₅H₂₀N₄S₂]⁺ 440.1 (100.0%), found 440.2 (100.0%). Anal. calcd for C₂₅H₂₀N₄S₂: C, 68.15%; H, 4.58%; N, 12.72%. Found: C, 68.00%; H, 5.02%; N, 12.55%.

Compound 11. Yellow powder in a yield of 0.11 g (26%). Yellow single crystals of compound 11 suitable for X-ray diffraction determination were grown from a solution of CHCl₃ by slow evaporation in air at room temperature for 10 days. Mp: 251–253 °C. Main FT-IR absorptions (KBr pellets, cm⁻¹): 2964 (w), 2931 (w), 2871 (w), 1662 (s), 1512 (w), 1442 (s), 1222 (m), 1049 (w), 802 (m), 742 (m), 663 (w). ¹H NMR (500 MHz, CDCl₃) δ: 9.93 (s, 1H, formyl), 9.20 (s, 2H, phen), 9.08 (d, 1H, J = 8.1 Hz, phen), 8.59 (d, 1H, J = 8.2 Hz, phen), 7.76 (m, 2H, phen; + 1H, thiophene), 7.50 (s, 1H, thiophene), 7.48 (s, 1H, thiophene), 7.40 (d, 1H, J = 3.7 Hz, thiophene), 4.79 (m, 2H, n-butyl), 2.11 (m, 2H, n-butyl), 1.57 (m, 2H, n-butyl), 1.06 (m, 3H, n-butyl). ¹³C NMR (125 MHz, CDCl₃) δ: 182.5, 149.2, 148.0, 146.2, 145.7, 145.0, 144.3, 142.6, 138.7, 137.2, 137.0, 133.3, 133.2, 130.5, 128.6, 127.9, 126.5, 125.7, 125.1, 123.8, 123.6, 122.7, 119.8, 47.0, 32.3, 19.8, 13.6. EI-TOF-MS (m/z): calcd for [C₂₆H₂₀N₄OS₂]⁺ 468.1 (100.0%), found 468.2 (100.0%). Anal. calcd for C₂₆H₂₀N₄OS₂: C, 66.64%; H, 4.30%; N, 11.96%. Found: C, 66.42%; H, 4.35%; N, 11.78%.

Compound 12. Yellow powder in a yield of 0.13 g (31%). Yellow single crystals of compound 12 suitable for X-ray diffraction determination were grown from a solution of CHCl₃ by slow evaporation in air at room temperature for 3 days. Mp: 242–244 °C. Main FT-IR absorptions (KBr pellets, cm⁻¹): 3060 (w), 2960 (w), 2923 (m), 2852 (w), 1666 (s), 1571 (w), 1521 (m), 1471 (m), 1382 (m), 1348 (w), 1274 (w), 1087 (w), 1037 (w), 958 (w), 790 (m), 769 (m), 734 (m), 707 (w). ¹H NMR (500 MHz, CDCl₃) δ: 9.67 (s, 1H, formyl), 9.16 (m, 2H, phen), 9.03 (d, 1H, J = 8.0 Hz, phen), 8.54 (d, 1H, J = 8.1 Hz, phen), 7.70 (m, 2H, phen) 7.60 (d, 1H, J = 2.7 Hz, thiophene), 7.50 (d, 1H, J = 2.7 Hz, thiophene), 7.33 (d, 1H, J = 2.5 Hz, furan), 6.80 (d, 1H, J = 2.5 Hz, furan), 4.75 (m, 2H, n-butyl), 2.06 (m, 2H, n-butyl), 1.52 (m, 2H, n-butyl), 1.02 (m, 3H, n-butyl). ¹³C NMR (125 MHz, CDCl₃) δ: 176.9, 153.6, 151.9, 149.2, 147.9, 146.1, 145.0, 144.3, 136.9, 133.9, 133.6, 130.4, 128.4, 127.8, 126.5, 125.6, 123.8, 123.5, 123.3, 122.6, 119.7, 108.6, 46.9, 32.2, 19.8, 13.6. EI-TOF-MS (m/z): calcd for [C₂₆H₂₀N₄O₂S]⁺ 452.1 (100.0%), found 452.1 (100.0%). Anal. calcd for C₂₆H₂₀N₄O₂S: C, 69.01%; H, 4.45%; N, 12.38%. Found: C, 68.88%; H, 4.48%; N, 12.21%.

Compound 13. Pale yellow powder in a yield of 0.41 g (82%). Yellow single crystals of compound 13 suitable for X-ray diffraction determination were grown from a solution of CHCl₃ by slow evaporation in air at room temperature for 3 days. Mp: 266–268 °C. Main FT-IR absorptions (KBr pellets, cm⁻¹): 3062 (w), 2972 (w), 2923 (w), 2871 (w), 1633 (s), 1560 (w), 1444 (m), 1390 (m), 1087 (m), 1045 (m), 798 (m), 746 (s), 707 (w), 621 (w). ¹H NMR (500 MHz, CDCl₃) δ: 9.20 (m, 2H, phen), 9.11 (d, 1H, J = 8.1 Hz, phen), 8.57 (d, 1H, J = 8.3 Hz, phen), 8.21 (m, 1H, dibenzothiophene), 8.19 (d, 1H, J = 7.8 Hz, dibenzothiophene), 7.92 (m, 1H, dibenzothiophene), 7.77 (m, 2H, thiophene), 7.75 (m, 1H, phen), 7.71 (m, 1H, dibenzothiophene), 7.64 (d, 1H, J = 3.8 Hz, dibenzothiophene), 7.57 (t, 1H, J = 7.7, 15.3 Hz, dibenzothiophene), 7.52 (m, 2H, dibenzothiophene), 4.80 (m, 2H, n-butyl), 2.12 (m, 2H, n-butyl), 1.58 (m, 2H, n-butyl), 1.07 (m, 3H, n-butyl). ¹³C NMR (125 MHz, CDCl₃) δ: 149.1, 147.7, 146.9, 145.5, 144.9, 144.3, 139.2, 137.5, 136.9, 136.8, 135.4, 131.5, 130.5, 128.8, 127.8, 127.2, 126.5, 126.2, 125.1, 124.7, 123.9, 123.5, 122.6, 121.8, 121.3, 119.8, 46.9, 32.3, 19.8, 13.7. EI-TOF-MS (m/z): calcd for [C₃₃H₂₄N₄S₂]⁺ 540.1 (100.0%), found 540.3 (100.0%). Anal. calcd for C₃₃H₂₄N₄S₂: C, 73.30%; H, 4.47%; N, 10.36%. Found: C, 73.13%; H, 4.51%; N, 10.19%.

Complex BM3. [RuCl₂(p-cymene)]₂ (0.50 g, 0.82 mmol) and 2 (0.90 g, 1.65 mmol) were added to dry DMF (40 mL), and the resulting mixture was heated at 80 °C under an argon atmosphere for 4 h. 4,4′-Dicarboxylic acid-2,2′-bipyridine (dcbpy; 0.40 g, 1.65 mmol) was added and the reaction mixture was heated at 160 °C for another 4 h in the dark. Excess NH₄NCS was added and the reaction mixture heated at 130 °C for 5 h. After the reaction, the solvent was removed by a rotary evaporator. Then, the solid was dissolved in a basic methanol (tetrabutylammonium hydroxide) solution and purified using a Sephadex LH-20 column with methanol as the eluent to obtain a red solid. The red solid was then dissolved in water and a few drops of 0.02 M HNO₃ were added. The precipitate was filtered and washed thoroughly with distilled water and dried in vacuo affording the final product BM3 in a yield of 0.33 g (20%). Mp >300 °C. ¹H NMR (DMSO-d₆, 500 MHz) δ: 9.61 (s, 1H), 9.52 (s, 1H), 9.18 (s, 1H), 8.99 (s, 1H), 8.38 (s, 1H), 7.84 (m, 4H), 7.61 (m, 4H), 7.51 (m, 3H), 7.34 (m, 4H), 7.08 (m, 6H), 6.98 (d, 2H, J = 7.4 Hz). ESI-MS (m/z): 1006.25 (100.0%) [M − H]⁻. Anal. calcd for C₄₉H₃₁N₉O₄RuS₃: C, 58.44%; H, 3.10%; N, 12.52%. Found: C, 58.13%; H, 3.56%; N, 12.28%.

Complex BM4. The synthetic procedure of BM4 was similar to that described for BM3, except that [RuCl₂(p-cymene)]₂ (0.21 g, 0.34 mmol), compound 9 (0.40 g, 0.67 mmol), dcbpy (0.16 g, 0.67 mmol) and excess NH₄NCS were used in the reaction. After purification, 0.18 g (25%) of product was obtained. Mp >300 °C. ¹H NMR (DMSO-d₆, 500 MHz) δ: 9.67–9.64 (m, 1H), 9.31 (s, 1H), 9.11 (m, 1H), 8.81 (s, 1H), 8.75 (s, 2H), 8.61 (s, 1H), 8.42 (m, 2H), 8.18 (s, 1H), 7.88 (s, 2H), 7.80–7.35 (m, 14H), 5.32 (s, 2H), 5.04 (s, 2H), 2.14 (s, 2H), 1.97 (s, 3H). ESI-MS (m/z): 1060.17 (100.0%) [M − H]⁻. Anal. calcd for C₅₃H₃₇N₉O₄RuS₃: C, 59.99%; H, 3.51%; N, 11.88%. Found: C, 59.61%; H, 4.11%; N, 11.46%.

Acknowledgements

This work was financially supported by the Major State Basic Research Development Programs (nos 2013CB922101 and 2011CB933300), the National Natural Science Foundation of China (nos 21171088 and 21021062), and the Natural Science Foundation of Jiangsu Province (Grant BK20130054).

Notes and references

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Footnote

† Electronic supplementary information (ESI) available: ¹H and ¹³C NMR, EI-TOF-MS and ESI-MS spectra, selected bond lengths (Å) and bond angles (°) and a view of the packing structures for related compounds. CCDC 1018234–1018245. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c4ra12627k

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