Regioisomers of carbazole- and triphenylamine-based D–A–D ternaries: synthesis, optical properties and colorimetric vapochromic anti-counterfeiting application

Abstract

In this study, we report two regioisomers, 1 and 2, having an asymmetric D–A–D (donor–acceptor-donor) architecture with carbazole and triphenylamine as donors and the carbonyl group as the acceptor. Isomers 1 and 2 exhibit fluorescence in both solid and solution states. Both the absorption and emission features of 1 and 2 are dominated by charge-transfer transitions. Reversing the positions of carbonyl and alkene groups between the two donors resulted in significant changes in the electronic energy levels, with variations in the absorption and emission features. A red-shifted absorption and fluorescence feature is observed in 1 with more quantum yield due to extended electron delocalization. A minor difference in the arrangement of α, β-unsaturated carbonyl groups led to different molecular packings in the solid state. As a result, isomer 1 displayed a higher fluorescence yield in its solid state than isomer 2. Finally, we utilized isomer 1 to develop a security ink as it forms reversible Lewis acid–base adducts with BF₃·OEt₂, accompanied by a stark color change from yellow to blue.