Benzimidazole and benzothiazole conjugated Schiff base as fluorescent sensors for Al3+ and Zn2+

Two benzimidazole/benzothiazole based azomethines, (E)-2-(1H-benzo[d]imidazol-2-yl)-4-(4-(diethylamino)-2-hydroxybenzylideneamino)phenol (HBZA) and (E)-2-(benzo[d]thiazol-2-yl)-4-(4-(diethylamino)-2-hydroxybenzylideneamino)phenol (HBTA) were designed and synthesised. Investigations of solvatochromic behaviour of these fluorophores in solvents of varying polarities showed large Stokes shift of 134-210 nm. Time resolved Laser induced fluorescence measurements revealed the excited state dynamics of the fluorophores. Molecules were also found to be emissive in aggregated state as seen from the aggregation induced emission studies. Appreciable absorption and emission spectral changes upon co-ordination of HBZA with Al3+/Zn2+ and HBTA with Al3+, as well as good sensitivity and selectivity, indicated their capability of detecting the two analytes. The binding stoichiometry was determined using electrospray ionization mass spectrometry (ESI-MS) and the binding mechanism was studied using density functional theory.