Optoelectronic Properties of A‐π‐D‐π‐A Thiophene‐Based Materials with a Dithienosilole Core: An Experimental and Theoretical Study

Two A‐π‐D‐π‐A thiophene based small molecules, with a central dithienosilole core and dicyanovinyl end groups were synthesized. These compounds differ only for the presence of alkyl and alkylsulfanyl chains, respectively, on thiophene beta positions. The computational data together with the spectroscopic and electrochemical findings (obtained by means of absorption, steady‐state/time‐resolved emission techniques and cyclic voltammetry) revealed that both molecules possess low electronic and optical band gaps, broad absorption spectra and a good stability both in p and n‐doping states, properties that make them suitable for optoelectronic applications. In either compounds the HOMO‐LUMO transition involves an intramolecular charge transfer from the electron‐donor dithienosilole unit to the two terminal electron‐acceptor DCV groups. A marked positive emission solvatochromism was observed for both molecules and was interpreted on the basis of the symmetry breaking in the S1 excited state. The two synthesized compounds were also compared to their shorter precursors and to similar oligothiophenes to understand how the nature of the building block influences the characteristics of the final materials. Furthermore, it was possible to better understand the contribution of the sulfur atom in modulating the optical properties of the small molecules studied.