Synthesis, Photophysical and Photovoltaic Properties of Conjugated Polymers Containing Fused Donor-Acceptor Dithienopyrrolobenzothiadiazole and Dithienopyrroloquinoxaline Arenes

We have developed two nitrogen-bridged pentacyclic donor-acceptor dithienopyrrolobenzothiadiazole (DTPBT) and dithienopyrroloquinoxaline (DTPQX) arenes where the two outer electron-rich thiophene moieties are covalently fastened with the central electron-deficient benzothiadiazole and quinoxaline cores by two nitrogen bridges. These rigid and coplanar DTPBT and DTPQX building blocks were copolymerized with fluorene (F), carbazole (C) and cyclopentadithiophene (CPDT) units via Suzuki or Stifle coupling polymerization to afford six new alternating copolymers PFDTPBT, PCDTPBT, PCPDTDTPBT, PFDTPQX, PCDTPQX and PCPDTDTPQX, respectively. The nitrogen bridges not only planarize the structure to induce stronger intermolecular pi-pi interaction but also play an important role in determining the electronic and photophysical properties of the polymers. The device based on PFDTPQX/PC71BM (1:4, w/w) exhibited a open-circuit voltage (V-oc) of 0.72 V, a short-circuit current (J(sc)) of 8.62 mA/cm(2) and a FF of 0.55 leading to a decent power conversion efficiency (PCE) of 3.40% due to the lower-lying HOMO energy level, and the highest hole-mobility of PFDTPQX