3D π-Conjugated Oligothiophenes Based on Sterically Twisted Bithiophene Nodes



3D conjugated architectures consisting of short oligothiophene chains attached to a connecting node formed by a sterically twisted bithiophenic system have been synthesized by various combinations of bromination and organometallic couplings. The analysis of the electronic properties of these systems by UV-vis absorption spectroscopy and cyclic voltammetry shows that the effective conjugation length depends on the twist angle in the central bithiophene node and on the number, length, and composition of the conjugated branches. A first evaluation of the potential of this new class of compounds for the realization of organic solar cells has been carried out. To this end two prototype bulk heterojunctions based on two representative compounds as donors and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as acceptor have been realized. A short-circuit current density of 1.33 mA cm–2 and a power conversion efficiency of 0.20 % have been measured under AM 1.5 (air-mass 1.5) simulated solar irradiation.