Effect of substitutions on different properties

Many papers have dealt with the computational study of substituted oligothiophenes. Most of these studies were connected to experimentally studied systems. Here we will summarize a few representative examples of theoretical studies. 

Despite the fairly good agreement observed between the theoretical and experimental results, a detailed analysis of the theoretical results indicated that calculations performed on planar conformations failed to rationalize simultaneously the experimental evolution of the reduction and oxidation potentials among the series of oligomers [45]. For instance, the fact that the oxidation potential is larger when the cyano group occupies a more central position in the trimer [as observed in the T5 T6 T7 series Chart 

In all systems, the lowest energy transition is mainly described by an electronic excitation between the HOMO and LUMO levels (with an additional contribution arising from the H - 1 L - - 1 excitation) [45]. Considering the oligothiophenes in their planar conformation, the cyano substitution leads to a red shift of the lowest optical transition because the derivatization gives rise to an asymmetric stabilization 

1507 (BAMQqT). By contrast, the chain length dispersion of the symmetric i s(C=C) vibrations reduces 1443 cm i (BAMTT), 1443 cm i (BAMQtT) and 1442 cm (BAMQqT). 

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