Telma
Costa
*a,
Diego
de Azevedo
a,
Beverly
Stewart
a,
Matti
Knaapila
b,
Artur J. M.
Valente
a,
Mario
Kraft
c,
Ullrich
Scherf
c and
Hugh D.
Burrows
a
aCentro de Química de Coimbra, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade de Coimbra, 3004-535 Coimbra, Portugal. E-mail: tcosta@qui.uc.pt
bDepartment of Physics and Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
cMacromolecular Chemistry Group, Bergische Universität Wuppertal, D-42119 Wuppertal, Germany
First published on 25th September 2015
In this paper we investigate the optical and structural properties of a zwitterionic poly[3-(N-(4-sulfonato-1-butyl)-N,N-diethylammonium)hexyl-2,5-thiophene] (P3SBDEAHT) conjugated polyelectrolyte (CPE) and its interaction in water with surfactants, using absorption, photoluminescence (PL), electrical conductivity, molecular dynamics simulations (MDS) and small-angle X-ray scattering (SAXS). Different surfactants were studied to evaluate the effect of the head group and chain length on the self-assembly. PL data emphasize the importance of polymer–surfactant electrostatic interactions in the formation of complexes. Nevertheless, conductivity and MDS data have shown that nonspecific interactions also play an important role. These seem to be responsible for the spatial position of the surfactant tail in the complex and, eventually, for breaking-up P3SBDEAHT aggregates. SAXS measurements on P3SBDEAHT-zwitterionic cocamidopropyl betaine (CAPB) surfactant complexes showed a specific structural organization of the system. The CAPB surfactant promotes a structural transition from pure P3SBDEAHT 3-dimensional aggregates (radius of gyration ∼85 Å) to thick cylindrical aggregates (∼20 Å) where all CAPB molecules are associated with the polymer. For molar ratios (in terms of the polymer repeat unit) >1 the SAXS interference maximum of the complexes resembles that of pure CAPB thus suggesting ongoing phase segregation in the formation of a “pure” CAPB phase.
Zwitterionic CPEs (ZCPEs) show advantages over regular, cationic or anionic CPEs due to the absence of mobile counterions. It has been shown that the size of the counterion can have a strong effect on the optical properties of CPEs. The UV/vis absorption spectra of 2,5-poly(thiophene-3-propionic acid) shifts over a 130 nm range by changing the counterion.11 This may be an advantage in some cases, since one can modulate the degree of aggregation in solution and hence its optical properties. Nevertheless, mobile counterions may also have negative effects on the performance of electronic devices as OLEDs or OFETs, due to luminescence quenching or alterations of work function of electrodes. Interlayers of zwitterionic CPEs can improve the electron injection and thus improve device performance.12–15 An OLED device containing an electrode interlayer of zwitterionic poly[(9,9-bis(N-(4-sulfonato-1-butyl)-N,N-dimethylammonium)ethyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] showed a very short response time (less than 10 μs). The localized nature of all ions near the cathodes facilitates charge injection, the current efficiency was enhanced by a factor of two.12 Zwitterionic polythiophene and poly(thiophene-alt-benzothiadiazole) derivatives were used as interfacial modification layers in organic photovoltaic devices and they greatly improved the power conversion efficiency (PCE) of organic solar cell (OSC) devices with Al or Ag cathodes.16 The PCE was enhanced >50% for an Ag cathode and 68% for an Al cathode, respectively.
ZCPEs also show promise for applications as sensing platforms. A polar polythiophene carrying amino acid side chains (POWT) can interact with positively or negatively charged peptides, as well as with four-helix bundles that were formed by the two peptide chains.17 Different polythiophene–peptide complexes are formed, with characteristic optical features. The differences are due to changes in the effective conjugation length and/or due to interchain interactions and aggregation effects. Similar effects are also found when POWT interacts with ss-DNA or ds-DNA.18,19 Hence, a detailed characterization of the ZCPE structure in the solid or (nano)aggregated state seems crucial in the development of new sensing platforms. In this study, we report the behavior of the zwitterionic P3SBDEAHT alone on water, and with various types of surfactants.
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Scheme 1 Synthesis of the conjugated, zwitterionic polyelectrolyte poly[3-(N-(4-sulfonato-1-butyl)-N,N-diethylammonium)hexyl-2,5-thiophene) (P3SBDEAHT). |
The P3BrHT sample used in the synthesis of P3SBDEAHT showed a number average molecular weight (Mn) of 11500 g mol−1 (corresponding to a degree of polymerization (DP) of 47) and a polydispersivity index (PDI) of 1.1. The detailed experimental procedure for P3SBDEAHT synthesis is outlined in the ESI.†
All the surfactants were purchased and used without any further purification, except for cocamidopropyl betaine (CAPB). CAPB was extracted from Dehyton® K 35 (BASF) through sodium chloride precipitation with ethanol. Sodium octyl sulfate (SOS), sodium dodecyl sulfate (SDS), sodium tetradecyl sulfate (STS), pentaethylene glycol dodecyl ether (C12E5) and hexadecyl trimethylammonium bromide (CTAB) were purchased from Sigma; dodecyl trimethylammonium chloride (DTAC) was purchased from Fluka. Milli-Q water was used in all solutions and the experiments were performed at the natural pH of the prepared solution.
The required species were added to a cubic box of 7 nm × 7 nm × 7 nm in accordance with the specifications given in Tables 1–3. The remainder of the cell was taken up by water by employing the SPC solvation model31 which considers a simple 3 point charge model for water where the intramolecular degrees of freedom are frozen and the intermolecular interactions are described by a combination of Lennard-Jones and Coulombic potentials between sites of fixed point-charges. The box was then constrained in accordance with the LINCS algorithm.32 Simulations were carried out over a time frame of 20 ns with a step size of 2 fs. All visualisations and images were generated using VMD software.33 The SPC model used represents, with accuracy, the properties of a bulk water environment under standard conditions, 300 K and 1 atmosphere pressure. It has also been employed in the study of similar CPEs in aqueous environments.34
Solvent | cac* (M) | cac (M) | cmc (M) | C surf (M) | λ abs (nm) | λ em (nm) | ϕ F |
---|---|---|---|---|---|---|---|
a Surfactant concentration at which the λabs, λem and ϕF were obtained. b ϕ F values were measured relative to α5 in methylcyclohexane (ϕF = 0.33).41 | |||||||
Water | — | — | — | — | 452 | 600 | 0.04 ± 0.002 |
Water | — | — | — | — | 452 | 600 | 0.043 ± 0.002 |
SOS | 1.45 × 10−2 | 1.3 × 10−1 | 1.33 × 10−1 | 0.14 | 428 | 571 | 0.074 ± 0.008 |
SDS | 1.16 × 10−3 | 5.91 × 10−3 | 8.3 × 10−3 | 1.0 × 10−2 | 433 | 574 | 0.113 ± 0.012 |
STS | 2.94 × 10−4 | 2.07 × 10−3 | 2.1 × 10−3 | 3.4 × 10−3 | 423 | 575 | 0.066 ± 0.003 |
CAPB | 8.1 × 10−5 | 9 × 10−5 | 1.1 × 10−4 | 444 | 593 | 0.054 ± 0.006 | |
DTAC | 1.96 × 10−2 | 2.03 × 10−2 | 2.4 × 10−2 | 443 | 594 | 0.053 ± 0.05 | |
CTAB | 7.5 × 10−4 | 9.2 × 10−4 | 1.0 × 10−3 | 438 | 594 | 0.12 ± 0.005 |
[P3SBDEAHT] (M) | T (°C) | cmc or cac* (mM) | α | (kJ mol−1) |
---|---|---|---|---|
SDS | 25 | 8.24 (±0.11) | 0.39 (±0.00) | −37.1 (±0.06) |
SDS/P3SBDEAHT (2.5 × 10−5 M) | 25 | 9.08 (±0.13)* | 0.31 (±0.00) | −36.53 (±0.06) |
SDS/P3SBDEAHT (6.2 × 10−5 M) | 25 | 9.28 (±0.36)* | 0.39 (±0.01) | −34.71 (±0.16) |
SDS/P3SBDEAHT (1.24 × 10−4 M) | 25 | 9.96 (±0.2)* | 0.39 (±0.00) | −34.43 (±0.08) |
DTAB | 25 | 15.0 (±0.12) | 0.23 (±0.00) | −36.06 (±0.04) |
DTAB/P3SBDEAHT (1.32 × 10−4 M) | 25 | 15.2 (±0.12)* | 0.23 (±0.00) | −36.00 (±0.04) |
CTAB | 25 | 1.02 (±0.009) | 0.27 (±0.00) | −46.77 (±0.04) |
CTAB/P3SBDEAHT (1.21 × 10−4 M) | 25 | 1.09 (±0.011)* | 0.32 (±0.01) | −45.14 (±0.06) |
[P3SBDEAHT] (M) | T (°C) | cmc or cac* (mM) | α | (kJ mol−1) | ΔGmic (J mol−1) |
---|---|---|---|---|---|
SDS | 25 | 8.24 (±0.1) | 0.39 (±0.00) | −35.27 (±0.05) | |
SDS/P3SBDEAHT | 25 | 9.28 (±0.36)* | 0.39 (±0.01) | −34.7 (±0.16) | 294 |
SDS | 30 | 8.19 (±0.45) | 0.38 (±0.02) | −35.33 (±0.23) | |
SDS/P3SBDEAHT | 30 | 8.14 (±0.25)* | 0.30 (±0.01) | −37.19 (±0.13) | −15.8 |
SDS | 40 | 8.22 (±0.1) | 0.39 (±0.04) | −35.15 (±0.05) | |
SDS/P3SBDEAHT | 40 | 7.87 (±0.1)* | 0.41 (±0.00) | −34.96 (±0.05) | −114 |
Similar effects were obtained with the addition of surfactants to an aqueous solution of P3SBDEAHT. The effect of nonionic (S0), anionic (S−), cationic (S+) and zwitterionic (S+/−) surfactants was studied and a quite different behavior was found that depends on the nature of the charged surfactants. The addition of cationic surfactants, dodecyl trimethylammonium chloride (DTAC) and hexadecyltrimethylammonium bromide (CTAB), caused similar effects on the optical properties of P3SBDEAHT (Fig. S1† and Table 1). Below the critical micelle concentration (cmc) of the cationic surfactant, the intensity, the maximum and the shape of the PL spectra does not significantly change (see Fig. S1, in the ESI†). When the surfactant concentration approaches the cmc, we can identify an increase of PL intensity and a blue-shift (by ca. 6 nm) of the spectra. The surfactant concentration at which these changes are observed corresponds to the critical aggregation concentration (cac). This concentration is, most probably, due to conformational changes of single P3SBDEAHT chains in P3SBDEAHT/anionic surfactant aggregates. Anionic sulfate surfactants (with chain lengths n = 8, 12 and 14, labeled as SOS, SDS and STS, respectively) induce different changes in the optical spectra of P3SBDEAHT when compared with cationic surfactants (Fig. 2 and 3). Upon addition of the anionic surfactant (csurf ≪ cmc), the PL intensity is first enhanced and the PL band is blue-shifted. The PL intensity continuously increases upon further addition of the surfactant. Starting at concentrations close to the cmc the PL intensity and emission maximum emission remain constant during further surfactant addition. In Fig. 3 one can identify two switching points for the dependence of PL intensity and λmaxvs. surfactant concentration. The first break occurs at concentrations well below the cmc and may be due to some disaggregation of interchain aggregates (so-called critical de-aggregation concentration cac* in Table 1). The second turn corresponds to the cac, also observed in P3SBDEAHT/S+ surfactant systems.
Comparing the optical responses of aqueous P3SBDEAHT solutions in the presence of single-tail surfactants with dodecyl chains (anionic SDS, cationic DTAC, and the non-ionic surfactant C12E5) the surfactochromic effect10 increases as follows: C12E5 < DTAC < SDS (Fig. 4 and Table 1). The hydrophobic interactions of the surfactant tails with P3SBDEAHT should be similar for the three systems. Therefore, the observed differences reflect the influence of electrostatic interactions of the head groups of the surfactants and the ionic side chains of the ZCPE. In fact, for the P3SBDEAHT(C12E5) system, no significant interaction was documented in the absorption and fluorescence spectra. However, this does not mean the absence of any interaction. Molecular dynamics simulations (MDS) provided evidence for the formation of P3SBDEAHT(C12E5) mixed aggregates (see bellow). The different effect promoted by SDS and DTAC is related to the position of the positively and negatively charged groups in the zwitterionic side chain. SDS interacts specifically with diethylammonium groups and the hydrophobic tail of the surfactant moves towards the hydrophobic domains of the polyelectrolyte. In the case of cationic surfactant DTAC, the polymer–surfactant interactions are non-specific and occur at the outer part of the zwitterionic chain. The tail of the cationic surfactant is not deeply embedded into the P3SBDEAHT–surfactant aggregate, explaining the weaker response in the photophysical properties of the polymer. This will be discussed more in detail in the MDS section.
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Fig. 4 PL emission spectra of P3SBDEAHT in aqueous solution containing surfactants with C12 tails: P3SBDEAHT(SDS), P3SBDEAHT(DTAC) and P3SBDEAHT(C12E5), at surfactant concentrations above the cmc. |
Addition of a zwitterionic surfactant, cocamidopropyl betaine (CAPB), to an aqueous solution of P3SBDEAHT leads to a gradual increase in the fluorescence intensity at concentrations slightly below the cmc, accompanied by a blue-shift of ca. 7 nm (see Fig. S2, in the ESI†). The effect on the optical properties is similar to that found for the cationic surfactant. The zwitterionic side chains of the P3SBDEAHT should cause strong dipolar interactions with the zwitterionic head group of CAPB. Here, the formation of a zipper-like arrangement similar to that found in the hydrogelation of a zwitterionic poly(fluorene-phenylene) may occur.19 However, the distance between the positively and negatively charged centers in the CAPB surfactant is significantly smaller than that in P3SBDEAHT. Therefore, a zipper-like arrangement is not likely; the interaction should mainly occur at the periphery of the zwitterionic side chain, similar to the interaction mode postulated for cationic surfactants, in accordance with the similar response of the optical properties during surfactant addition.
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Fig. 5 Effect of the addition of DTAB (a), CTAB (b) and SDS (c) on the electrical conductance (Δκ) of P3SBDEAHT, at 25 °C. The κ of the pure surfactant systems are also shown. |
Interactions between cationic surfactants (DTAB and CTAB) and P3SBDEAHT show that the presence of the CPE does not change the cmc (Fig. 5a and b). However, a slight increase in the degree of dissociation of counterions is noted for CTAB. This change is enough to increase the Gibbs energy of micellization for ca. 1.5 kJ mol−1, suggesting that the polymer aggregation is dependent on the hydrocarbon chain length (reasons behind this increase in the ΔG0 algebraic value will be discussed below). On the basis of our MDS discussion, it is proposed that alkyltrimethyl ammonium surfactants do not significantly affect the aggregation of P3SBDEAHT and the interactions between surfactants and polymers mainly occur on the outer region of the polyelectrolyte aggregates. This suggests that the interactions are weaker and mainly driven by hydrophobic interactions, and, consequently, the EC response is very weak.
A significantly different behavior is observed with the SDS-P3SBDEAHT system. Comparing the effect of the polyelectrolyte on the free energy of micellization of SDS with that obtained for DTAB, one can conclude that for similar P3SBDEAHT concentrations, an anionic surfactant induces a more significant change in the formation of surfactant micelles (−34.43 kJ mol−1vs. −37.1 kJ mol−1 for pure SDS and −36.00 kJ mol−1vs. −36.06 kJ mol−1 for pure DTAB). Such a change cannot be thermodynamically justified unless a given amount of SDS (labeled as [S]*) has been reacted with the polyelectrolyte in such a way that the effective cmc should be calculated by subtracting [S]*.42 To test the validity of this hypothesis, the dependence of cac on the polyelectrolyte concentration has been evaluated (see Table 2). A plot (not shown) of cac = f[P3SBDEAHT] results in a linear dependence with a slope of ca. 15.2 (R2 = 0.9987). A different point arises from this discussion: if there is an interaction between the ZCPE and the surfactant, it should be expected that a further turning point at pre-micelle concentrations of the surfactant should be detectable43 (Fig. 5) as observed in the fluorescence measurements (Fig. 3). However, the two techniques monitor different physical quantities and, consequently, different structural phenomena. Whilst fluorescence is able to follow changes in the polymer backbone, the conductivity depends mainly on the charge density of ionic species in solution. From that it arises that most probably the interaction between SDS and the polyelectrolyte is characterized by weak electrostatic interactions and, consequently, cannot be monitored during electrical conductance measurements. This seems to agree with MDS studies where the presence of the anionic surfactant SDS breaks up the polyelectrolyte aggregates in contrast with the cationic DTAB, thus highlighting the importance of the kind of charge in the surfactant. This was corroborated by measuring the cac of SDS in aqueous solutions of P3SBDEAHT at different temperatures (Table 3). By increasing the temperature the electrostatic interactions between the negatively charged dodecylsulfate and the positively charged P3SBDEAHT increase and lead to an increasing ionic mobility and, consequently, to a gain in the free energy of micellization, computed according to the following equation:
EC measurements for the interaction between zwitterionic P3SBDEAHT and zwitterionic CAPB were also carried out but, as expected, no significant changes or turning points in the electrical conductance plots were observed for increasing surfactant concentration.
Sample | [P3SBDEAHT] (mg mL−1) | [CAPB] (mg ml−1) | Analyzed q-range | α | Model | D max (Å) | R g (Å) | R CS,g (Å) | Peak (Å−1) |
---|---|---|---|---|---|---|---|---|---|
a α, Dmax, Rg, and RCS,g, are, respectively, the scattering power, considered maximum size of the particle (particle size or rod diameter) and the radius of gyration for the whole arbitrary-shaped particle or for the cross section of a cylindrical particle. Also shown is the position of an interference maximum for the CAPB sample. | |||||||||
P3SBDEAHT | 3.00 | 0.009–0.43 | — | 3D | 300 | 87.7 ± 1.3 | — | — | |
P3SBDEAHT | 5.58 | 0.009–0.43 | — | 3D | 300 | 82.3 ± 1.3 | — | — | |
P3SBDEAHT | 9.06 | 0.009–0.43 | — | 3D | 300 | 87.7 ± 0.8 | — | — | |
P3SBDEAHT – LMW | 9.06 | — | 0.014–0.25 | — | 3D | 60 | 21.1 ± 0.1 | — | |
P3SBDEAHT(CAPB) x = 0.2 | 7.48 | 1.58 | 0.01–0.15 | 1.14 ± 0.02 | Cylinder | 25 | — | 8.2 ± 0.1 | — |
P3SBDEAHT(CAPB) x = 0.54 | 5.89 | 3.17 | 0.01–0.15 | 1.11 ± 0.01 | Cylinder | 22 | — | 7.2 ± 0.1 | — |
P3SBDEAHT(CAPB) x = 1.0 | 4.53 | 4.53 | 0.01–0.15 | 1.13 ± 0.01 | Cylinder | 18 | — | 5.8 ± 0.1 | — |
CAP | 9.06 | — | — | — | — | — | — | 0.12 |
Fig. 6(b) shows the plots for P3SBDEAHT(CAPB)x for x = 0.2–5. The curves for pure P3SBDEAHT and CAPB are shown for comparison. Like P3SBDEAHT, CAPB shows increasing scattering at low scattering angles pointing to the aggregation of surfactants. While P3SBDEAHT curves are featureless, CAPB is showing a distinctive interference maximum at 0.12 Å−1 corresponding to the periodicity of 52 Å. It is not clear whether this peak stems from the internal structure of CAPB aggregates or from their electrostatic interactions.
Since both P3SBDEAHT and CAPB are zwitterionic, this combination allows nominal charge neutralization at x = 1. The data of P3SBDEAHT(CAPB)x differs from their constituents indicating the emergence of a new structural organization. For q < 0.15 Å−1 the curve decays as q−1 for all x. For q > 0.15 Å−1 the curves remain featureless scaling as q−4. We interpret these observations as an existence of ∼20 Å thick cylindrical aggregates where all CAPB molecules are associated with the polymer. The emergence of cylindrical aggregates and no sign of interference maxima are analogous to the phase behavior of a polymer–surfactant pair with both constituents containing only one (but opposite) charge, when the molar fraction x is screened over the nominal charge compensation point.8,9 Furthermore, these data are reminiscent to the rigid rod polyelectrolytes with strong clustering of counterions around the polymer chain.44 When the CAPB fraction is increased for x > 1, the data show an interference maximum similar to that of pure CAPB. This is a sign of an emerging phase segregation of pure CAPB.
The P3SBDEAHT(SDS)x system was also studied through SAXS (see Fig. S3†). For x = 0.2–1 the scattering curve displays a broad peak at q ≈ 0.18 Å−1. Free SDS micelles show a similar peak that stems from the polar cell of the surfactant heads45 and this points to the emerging phase separation even below x = 1. This was confirmed through EC, where the break in the conductivity curves was assigned to the formation of pure SDS micelles co-existing with P3SBDEAHT-SDS unimer aggregates (Fig. 5c). Molecular dynamics simulations showed that these merge into large P3SBDEAHT-SDS aggregates (see below). The fact that these are not observed through SAXS may indicate that the size of the aggregates is out of our detection range. The structural organization of the P3SBDEAHT(SDS)x system differs from that found with cationic P3TMAHT38,46 and S− surfactants, and may explain some of the optical differences found when we compare the ZCPE– and the cationic CPE–surfactant systems. The optical changes of cationic P3TMAHT(SDS)x and P3TMAHT(SOS)x systems are accompanied by phase transitions from charged P3TMAHT aggregates with interparticle order to rod-like and sheet-like particles with embedded polymer bundles or sheet-like polymer associations. The emergence of vibronic structures for charge ratios lower than 1/2 and phase separation, i.e., dissolved and precipitated phases co-exist in equilibrium, at nominal charge compensation, are also observed.46 In the present study, the PL band is structureless in the range of S− concentration studied and phase separation was not observed. Independently of the charge of the surfactant, the optical properties of the system can be modulated by changing surfactant concentration without the risk of precipitation. Different surfactants will promote different chain conformations due to their different packing within the aggregate. This is an important property of these polymer–surfactant systems from the solution processing point of view.
The simulation cells at 20 ns with different P3SBDEAHT:
S+ surfactant (DTAC and CTAC) ratios show a clear interaction between the S+ and the ZCPE (Fig. S4† and 7, respectively). The interaction appears to occur predominantly on the outer region of the surfactant
:
P3SBDEAHT aggregates. The localization of the interaction with S+ surfactants confirms the minimal effect on the polymer backbone, and hence on the effect on the conjugation length of the ZCPE.
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Fig. 7 Simulation cell of P3SBDEAHT and CTAB in (a) 1![]() ![]() ![]() ![]() ![]() ![]() |
Anionic surfactants with three different chain lengths (SOS, SDS and STS) had greater effect in the aggregation behavior of P3SBDEAHT tetramers, than S+. Fig. 8(a) shows the effects of the addition of SOS to P3SBDEAHT. Interaction clearly occurs at each of the three ratios although some solubility of the surfactant is apparent in each case. Comparable observations were found upon addition of SDS (Fig. 8(b)) although with a lesser amount of surfactant solubility is observed. The overall system does appear to be more disperse and it can be observed that aggregation of P3SBDEAHT is inhibited. At the highest surfactant:
polyelectrolyte ratio this seems to result in the formation of a large surfactant–polyelectrolyte aggregate (see Fig. 8 right hand panels). A similar behaviour was also found for addition of STS, Fig. 8(c). At the lowest ratio there is a clear interaction between the P3SBDEAHT and STS. In this case the aggregates formed appear to be better defined than what was observed for SOS and SDS. As the ratio of the anionic surfactant to the electrolyte increases it becomes very clear that a rather specific interaction is occurring where the tail groups of the surfactant have become noticeably embedded in the surfactant/polyelectrolyte aggregate and the head groups remain exposed to the surrounding solvent.
In the presence of zwitterionic CAPB there is a clear interaction between the polyelectrolyte and the surfactant through the formation of mixed P3SBDEAHT(CAPB) aggregates (Fig. S5†). However, although it is extremely likely that those interactions are governed primarily to minimise unfavourable electrostatic interactions, it is possible that these reorientations do not significantly affect the structural arrangement of P3SBDEAHT and resultantly do manifest as minor changes in spectroscopy measurements.
Simulations of P3SBDEAHT and C12E5 show that interaction does occur between the polyelectrolyte and the surfactant (Fig. S6†) but it is possible that the hydrophobic tail group of the surfactant is too long to embed into the zwitterion aggregate sufficiently to cause any structural or electronic changes that could be detected by spectroscopy or photochemical techniques. This suggests that the interaction between the nonionic surfactant and the polyelectrolyte takes place predominantly on the outer part of the polyelectrolyte aggregates and has little effect on P3SBDEAHT.
We believe our results are valuable in the field of conjugated polyelectrolytes: the combination of photophysical, molecular dynamics and small angle X-ray scattering analysis allows us to derive a detailed picture of the interaction of a zwitterion polythiophene with a range of surfactants. Recently, the occurrence of photoinduced electron-transfer cascades has been shown for poly(fluorene-alt-thiophene)/cationic fullerene assemblies leading to long-lived and stable polaron pairs.47 Finally, the detailed understanding of the surfactochromic behavior of conjugated (zwitter)ionic polyelectrolytes is of high importance for the design of new functional materials for use in solution processed optoelectronic devices and as biosensors.
Footnote |
† Electronic supplementary information (ESI) available. See DOI: 10.1039/c5py01210d |
This journal is © The Royal Society of Chemistry 2015 |