Phenyl selenoxide functionalized TPA/TPE π-conjugated imidazo[1,2-a]pyridine: a fluorescent probe for the selective detection of water in organic solvents

Abstract

Phenyl selenoxide functionalized tetraphenylethylene (TPE) and triphenylamine (TPA) electron donors π-conjugated with the imidazo[1,2-a]pyridine acceptor, namely, N,N-diphenyl-4-(3-(phenylseleninyl)imidazo[1,2-a]pyridin-2-yl)aniline (SeO-TPA) and 3-(phenylseleninyl)-2-(4-(1,2,2-triphenylvinyl)phenyl) imidazo[1,2-a]pyridine (SeO-TPE), were synthesized, and the effect of TPA/TPE on their photophysical properties was explored. SeO-TPA showed emission in both solution and solid states, while SeO-TPE exhibited emission only in the solid state. SeO-TPA also exhibited solvent polarity-dependent emission due to a hydrophilic SeO group. Interestingly, the selenoxide of SeO-TPA reacted with a trace amount of water present in the organic solvents and produced dihydroxy selenane derivatives. The structural transformation of selenoxide (SeO-TPA) to dihydroxy selenane (Se(OH)₂-TPA) resulted in fluorescence changes from 448 nm to 420 nm. The reduction of electron-withdrawing character by converting selenoxide to dihydroxy selenane resulted in a blue shift of the emission. The concentration-dependent studies of SeO-TPA indicated that the probe can detect water in organic solvents up to 0.429 wt% in CH₃CN, 0.602 wt% in ethanol, 1.108 wt% in DMF, 0.514 wt% in DMSO, and 1.028 wt% in THF. Hence, this work reported on a naked-eye detectable fluorescence probe for sensing trace amounts of water in organic solvents, highlighting its potential applications in environmental and analytical chemistry.