I ₂ /H ₂ O ₂ mediated synthesis and photophysical properties of imidazole-fused heterocycles via [4+1] cyclization approach

An efficient I ₂ (10 mmol%)/H ₂ O ₂ mediated oxidative formal [4+1] cyclization of 2-pyridinemethylamine or o-phenylenediamine (2-aminobenzenethiol) with benzaldehyde via C-N bond formation has been developed. This strategy offers a straightforward approach to imidazo[1,5-a]pyridine and benzimidazole (benzothiazole) derivatives in 65% to 98% yields. Several heterocyclic products exhibit promising blue luminous performance with satisfactory fluorescence quantum yields of up to 64%, large Stokes shifts, and a longer lifetime (7.35 ns). The band gap energies obtained from DFT are also consistent with the absorption spectra.