Self-association of oligothiophenes in isotropic systems

Abstract

The self-association equilibrium constants, Kass, for the dimerization of some small oligothiophenes in acetone, acetonitrile and chloroform were measured by (1)H NMR spectroscopy. The gas phase interaction energies for some oligothiophene dimers were determined by computational quantum chemistry. The (1)H NMR results indicate that Kass generally increases with the chain length (the number of thienyl rings, n) and solvent polarity; however, Kass for thiophene (n = 1) was found to be higher than for the bithiophenes (n = 2). The linear oligothiophenes 2,2'-bithiophene and 2,2',5',2''-terthiophene were found to self-associate less than their corresponding nonlinear isomers 3,3'-bithiophene and 3,2',5',3''-terthiophene in solution and in the gas phase. For α-quaterthiophene (n = 4) Kass in solution was found to be smaller than expected. The non-linear dependence of the standard molar Gibbs energy of self-association, ΔassG, on the chain length in solution could be nicely reproduced and related to the conformational entropy change of dimerization. It was observed that the melting properties of oligothiophenes correlate well with their tendency to self-associate, with more self-association leading to increased liquid stability, and thus lower melting temperatures. These results highlight the relevance of self-association in isotropic systems for the correct molecular interpretation of phase equilibria.

High-Field-Effect Mobility of Low-Crystallinity Conjugated Polymers with Localized Aggregates

“…Moreover, broad peaks were observed between 7.07 and 7.12 ppm (yellow box, Figure a), consistent with the presence of more than two successive thiophene units in RP17 , RP25 , and RP33 . For thiophene oligomers, proton peaks for the central units appear between those of their terminal analogues. − These broad peaks grow when the thiophene content increases because the probability for one thiophene unit to bind another rises.…”

Conductivity, interaction and solubility of hetero‐bifunctional end‐capped β,β’‐dihexylsubstituted sexithiophenes

“…It is known from literature that aldehyde endcapping can somewhat improve the properties of a sexithiophene. Dialdehyde T6.2 also self‐associate in chloroform, based on NMR shift differences at different concentrations, whereas the other sexithiophenes show no such association. The self‐association constant was calculated to be 1.6 (mol kg −1 ) from the NMR shift differences, see Figure (also see Table SI in Supporting Information).…”

Effect of Self-Association on the Phase Stability of Triphenylamine Derivatives

“…The observed behavior is consistent with the formation of stacked dimers in solutionas the concentration of TPD increases, the self-association equilibrium is shifted in the direction of forming more dimer and the observed signals shift upfield. 19,33 The Δδ = f(concentration) correlation showed a significantly more pronounced curvature for TPD than for mMTDAB, evidencing that, in contrast to TPD, mMTDAB does not self-associate to any significant extent in CDCl 3 solution. For this reason it was only possible to derive a reliable value for the self-association equilibrium constant, K ass , for TPD.…”

“…It is interesting to note that, on comparison of the selfassociation results for the triphenylamines studied herein and the oligothiophenes, 19 greater thermodynamic differentiation in the liquid phase between interrelated compounds occurs for those presenting greater differences in K ass (in this case TPB and TDAB). This further supports that self-association significantly influences the thermodynamic stability of the liquid phase and hence leads to observable changes in phase equilibria.…”

“…Knowing and understanding the thermodynamic properties of these compounds is of prime importance for their rational and successful application as OSCs. In a recent work we have shown that self-association in oligothiophenes can significantly influence their thermodynamic properties: namely, increasing the stability of the liquid phase and consequently contributing to a decrease of the melting temperature . Self-association can also promote some degree of organization and structuration at the nanoscale in apparently isotropic media.…”