Carbazole-based compounds containing aldehyde and cyanoacetic acid: optical properties and applications in photopolymerization

Carbazole-based dyes containing aldehyde and cyanoacetic acid groups were synthesized through Sonogashira coupling and Knoevenagel reactions. These compounds included 6-((4-(diphenylamino) phenyl) ethynyl)-9-ethyl-9H-carbazole-3-carbaldehyde (CCC), 9-ethyl-6-((9-ethyl-9H-carbazol-3-yl) ethynyl)-9H-carbazole-3-carbaldehyde (TCC), (E)-2-cyano-3-(9-ethyl-6-((9-ethyl-9H-carbazol-3-yl) ethynyl)-9H-carbazol-3-yl) acrylic acid (CCN) and (E)-2-cyano-3-(6-((4-(diphenylamino) phenyl) ethynyl)9- ethyl-9H-carbazol-3-yl) acrylic acid (TCN). Density functional theory (DFT) calculations revealed these structures to be coplanar-conjugated molecular and uniform in shape. The UV spectra showed three main absorption peaks from 240 nm to 400 nm, indicating pi-pi* and n-pi* electron transitions. The calculated vertical singlet excitation energy was within the range of n-pi*. This finding was confirmed based on the acceptor results in reduced highest occupied molecular orbital-lowest unoccupied molecular orbital gap by launching cyanoacetic acid. These functional compounds could be used as dyes/photosensitizers.