Diazapentalene-Containing Ultralow-Band-Gap Copolymers for High-Performance Near-Infrared Organic Phototransistors

Because of the limited availability of synthetic strategies and strong acceptor units, constructing new types of low-band-gap donor–acceptor-type copolymers for use in multiple functional applications remains a big challenge. Herein, we report the synthesis, characterization, and optoelectronic applications (i.e., organic field-effect transistors (OFETs) and organic phototransistors (OPTs)) of a novel class of ultralow-band-gap copolymers (PDAP–Fu, PDAP–Th, and PDAP–Se) on the basis of the unique, interesting, yet rarely researched bicyclic 2,5-diazapentalene (DAP) strong acceptor in conjugation with chalcogenophene donors (furan (Fu), thiophene (Th), or selenophene (Se)). All of the copolymers exhibit broad near-infrared (NIR) absorption and optical band gaps as low as ∼1.0 eV. The effects of the actual chalcogen atoms on the geometry, optical properties, energy levels, and film organiz…