Oligothiophenes cyano-substituted

Cyano-substituted oligothiophene 2.57 (Chart 1.13) was prepared by Suzuki-type coupling reaction between 5-bromo-5"-cyanoterthiophene and the bis-boronic acid of the inner terphenyl building block... 

Table 2. Energy (in eV) of the HOMO and LUMO levels, lowest transition energy (Eu, in eV) and related oscillator strength (OS, in arbitrary units) of the coplanar cyano-substituted oligothiophenes in a planar conformation, as provided by INDO/SCI calculations. We present in parentheses the INDO shifts of the frontier levels (with respect to a reference compound in each group) that are compared to the corresponding experimental values appearing in bold [80].

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... 

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