Band gap tunable for near-infrared absorbing chromophores with multi-triphenylamine and tris (thieno)hexaazatriphenylenes acceptors

Two disk-like D–A type chromophores with multi-triphenylamine donors and hexaazatriphenylenes acceptors were synthesized and fully characterized by 1H and 13C NMR, elemental analysis and mass spectrometry. The effects of the hexaazatriphenylene on the optical and electrochemical properties and band gap of the chromophores were investigated. As the hexaazatriphenylene core fused with three thiophene rings, the band gaps of the compounds could be tuned from 1.65 eV to 1.15 eV. The π–π* absorption peak and charge-transfer absorption peak of the hexaazatriphenylene compounds were red shifted from visible spectrum region (393 and 530 nm) to near-infrared spectrum region (542 and 756 nm). In addition, due to an increase in the π electronic coupling between electron donor and electron acceptor, the extinction coefficient (charge-transfer absorption) of the hexaazatriphenylene compound decreases 85% from 3.4 × 104 mol−1 dm−3 cm−1 to 0.5 × 104 mol−1 dm−3 cm−1.