Towards molecular design rationalization in branched multi-thiophene semiconductors : the 2-thienyl-persubstituted alpha-oligothiophenes

The introduction of branching in multi-thiophene semiconductors, while granting the required solubility for processing, results in an increased molecular fluxionality and in a higher level of distorsion, hampering p-conjugation. Accordingly, branched oligothiophenes require rationalization of their structure-reactivity relationships for target-oriented design and optimization of the synthetic effort. Our current research on spider-like oligothiophenes affords a deep insight on the subject, introducing at the same time new, easily accessible molecules with attractive functional properties. In particular, a new regular series, T’XY, of five new multi-thiophene systems, T’53, T’84, T’115, T’146, and T’177, constituted by five, eight, eleven, fourteen, and seventeen thiophene units respectively, their longest a-conjugated chain consisting of ter-, quarter-, penta-, hexa-, and hepta-thiophene moieties, has been synthesized and fully characterized from the structural, spectroscopic, and electrochemical point of view. The electronic properties of the monomers and their electropolymerization ability are discussed and rationalized as a function of their molecular structure, particularly in comparison with the series of the 5-(2,2’-bithiophene)yl-persubstituted a-oligothiophenes (TXY) previously reported by us. These oligothiophenes are easily accessible materials, with promising properties for applications as active layers in multifunctional organic devices including solar cells