Combined Raman, electrochemical and DFT studies on a series of α, α′-thiophene-phosphole oligomers and their corresponding polymers

In this work we study three homologues of terthiophene in which the innermost sulphur atom has been replaced by a phosphorous one, namely, 2,5-bis(2-thienyl)phospholes. This strategy pursuits to improve the optical and electronic properties of oligomers derived from thiophene by means of the modulation of their conjugational properties. The assignment of the Raman bands of the phosphole derivatives and their correlation among the series of molecules allows to compare their electronic structures with that of the thiophene counterparts. We have found a disruption of the whole electronic structure on passing to the phospholes, which can be in agreement with the already well known lacking of aromatic character of phosphole as compared with thiophene. Raman spectroscopy also proves effective in addressing sigma-pi conjugation between pi-chromophores of a dimer connected through a P-P bond in neutral state.