Conformational control of the electronic properties of an α-β terthiophene: lessons from a precursor towards dendritic hyperbranched oligo- and poly-thiophenes.

Herein we investigate the conformational and electronic properties of the 2,2';3',2"-terthiophene (B3T) unit as the building block of thiophene dendrimeric materials. By means of DFT ground electronic state dihedral energy profiles, we get insight in the flexibility of B3 T as the prominent feature promoting the 3D arrangement. The presence of diverse conformers is explored by Raman and (1)H NMR spectroscopies. A theoretical estimation of the Raman and (1)H NMR spectra over the most energetically accessible conformers is found to be crucial for the appropriate assignment of the major conformer population derived from the experimental spectra. We show that energy barriers for the interconversion of conformers also play a role. Finally, the impact on the optical spectra (absorption and emission) of the α-α and α-β connections is studied and addressed by scanning the properties of the relevant low-lying excited states. These studies highlight the relevance of the architecture of the basic molecular unit to understand charge and exciton behavior in organic semiconductors, particularly for those useful in photovoltaics.