Phase transition, optical and photoconductive properties of bay-substituted benzoporphyrin derivatives

Abstract

Two benzoporphyrin derivatives substituted with long side chains at the bay positions have been synthesized through a facile route. They were confirmed to show two separate columnar phases upon cooling, i.e., a hexagonal columnar phase and a rectangular columnar phase. In particular, the temperature dependence of the electronic spectra revealed that the Q-band split into two peaks, indicating the existence of typical herringbone-type dimers. Moreover, their photoconductive properties were studied by steady-state and transient photocurrent measurements. It was found that both benzoporphyrins exhibited very fast hole mobility over 0.1 cm² V⁻¹ s⁻¹ in both columnar phases and a high charge carrier generation efficiency up to 2%, demonstrating that they are potential p-type organic semiconductors for photovoltaic devices.