Influence of Thiophene Moiety on the Excited State Properties of Push–Pull Chromophores

The magnitude of intramolecular charge-transfer (ICT) in push–pull chromophores and the fraction of delocalized excitation in multibranched chromophores and conjugated polymers play a crucial role in high photovoltaic efficiency of a solar cell. In this work, we present a joint theoretical and experimental study aimed to understand the influence of thiophene moiety on photophysical properties of push–pull chromophores for solar cell application. It is found that insertion of a thiophene moiety as the conjugated bridge enhances the magnitude of ICT in push–pull chromophores due to the inductive effect of the thiophene moiety. In addition, introduction of a thiophene moiety as the conjugated side chain significantly increases transition dipole moment of the chromophore, and as a consequence, interchromophoric coupling is enhanced, giving rise to a larger fraction of delocalized excitation within multibranched chromophores. The results presented here show that introduction of a thiophene moiety in push–pull chromophores contributes to the improvement of the photophysical properties necessary for highly efficient solar cell performance.