Dithienopyrrole-quinoxaline/pyridopyrazine donor-acceptor polymers: Synthesis and electrochemical, optical, charge-transport, and photovoltaic properties

Soluble alternating copolymers of N-(3,4,5-tri-n-dodecyloxyphenyl) dithieno[3,2-b:2′,3′-d]pyrrole donor groups and 2,3-di-n- decylquinoxaline, 2,3-di-n-decylpyrido[3,4-b]pyrazine, 2,3,6,7-tetrakis(n- decyloxy)benzo[a,c]phenazine, or 2,3,6,7-tetrakis(n-decyloxy)dibenzo[f,h] pyrido[4,3-b]quinoxaline acceptors were synthesised using Stille coupling reactions. Experimental absorption maxima in THF range from 645 to 770 nm. These optical data, along with the results of quantum-chemical calculations and electrochemical measurements, show that, as expected, the pyridopyrazine moiety acts as a stronger acceptor than quinoxaline and that the extended species benzophenazine and dibenzopyridoquinoxaline are stronger acceptors than quinoxaline and pyridopyrazine, respectively. Modest average hole mobilities of up to ca. 3.0 × 10^-4 cm² V^-1 s ^-1 were obtained in field-effect transistors. Bulk heterojunction photovoltaic devices made from blends of the benzo[a,c]phenazine-based polymer with 3′-phenyl-3′H-cyclopropa[1,9](C₆₀-I _h)[5,6]fullerene-3′-butanoic acid methyl ester (1:3 weight ratio) exhibited average power conversion efficiencies up to 1.4%.