Unusual blue-shifted acid-responsive photoluminescence behavior in 6-amino-8-cyanobenzo[1,2-b]indolizines

Abstract

6-Amino-8-cyanobenzo[1, 2-<i>b</i>]indolizines, a new class of photoluminescent materials, exhibit reversible pH-dependent optical properties characterized by an uncommon and dramatic blue shift in fluorescence emission when protonated. Acid titration and NMR spectroscopy experiments reveal that, rather than the anticipated N-protonation, C-protonation and loss of aromaticity is responsible for the observed photophysical changes. Efficient synthesis from indole-2-carboxaldehydes makes variously substituted versions of this nucleus readily available to tune optical and pH effects.