New Quinoxaline-Containing Monomers for Narrow-Bandgap Polymers

Two new fused quinoxaline-containing monomers—2,3-bis(9-(2-decyltetradecyl)-9H-carbazol-3-yl)dithieno[3,2-f:2'3'-h]quinoxaline (М1) and 2,5-di(nonadecan-3-yl)bis[1,3]thiazolo[4,5-a:5',4'-c]bisthieno[3,2-h:2',3'-j]phenazine (М2)—have been synthesized in high yields of 88 and 83% as promising building blocks of D-A polymers for photovoltaic applications. The optical bandgaps, found from the absorption edge, are 2.79 and 2.88 eV, respectively. The HOMO/LUMO energies of М1 and М2 are–5.83/–2.96 and–5.83/–2.98 eV, respectively. Both monomers have low-lying HOMO levels, which is favorable for a high open-circuit voltage and a high stability in air in the development of PSCs. The E g ec values of monomers М1 and М2 are 2.87 and 2.85 eV and are consistent well with the optical bandgap (2.79 and 2.88 eV, respectively).