Charge–Transfer Complexes and Fluorescence Modulation in Amide- and Carboxy-Substituted 2-Phenyl-1,3,2-benzodiazaboroles

A library of amide- and carboxy- functionalized 2-phenyl-1,3,2-benzodiazaborole derivatives was synthesized via microwave-assisted cyclic condensation to explore the effects of pseudoaromaticity on charge-transfer complex (CTC) formation and photophysical behavior. All compounds were characterized by NMR, IR, UV-vis, and fluorescence spectroscopy. While absorbance profiles remained consistent (λ_max = 298 - 324 nm), several derivatives exhibited strong bathochromic emission (λ_em = 363 - 555 nm) and exceptionally large Stokes shifts (Δ<i>v</i> > 150 nm), particularly those bearing -OCH₃ groups. Red-shifted fluorescence and DFT calculations suggest antiparallel dimeric CTCs stabilized by B-N delocalization. These results highlight amide- and carboxy- 1,3,2-benzodiazaborole frameworks as tunable pseudoaromatic systems with potential applications in optical sensing and functional material design.