Synthesis and photophysical properties of fluorescent arylstyrylimidazo[1,2-a]pyridine-based donor-acceptor chromophores

A series of novel fluorescent arylstyrylimidazo[1,2-a]pyridines was synthesized and fully characterized. All styryl derivatives have an E-configuration of the vinyl double bond as unequivocally shown by H-1 NMR spectroscopy. It was observed that the E isomers are stable in the solid state; however, the derivatives with strong electron donating dialkylamino substituents underwent partial E-Z isomerization in solution at room temperature. The styryl derivatives absorb in the UV or visible region and emit light with moderate Stokes shifts. These compounds exhibit fluorosolvatochromism, namely the emission band is red shifted with increasing solvent polarity. Moreover, the absorption and emission properties of the styryl derivatives change drastically upon acidification, as the protonation of the nitrogen atoms of the imidazo[1,2-a]pyridine ring increases the donor-acceptor interplay of the pi system. (C) 2014 Elsevier Ltd. All rights reserved.