Abstract
While it is known that fluorescence is often quenched in the solid state due to intermolecular interaction, there is a growing interest in organic compounds that display enhanced luminescence in the solid state. Several derivatives of 2-(2'-hydroxyphenyl)imidazo[1,2-a]pyridine (1) have been synthesized and properties of the solid-state ESIPT luminescence are studied. Though they show only a weak ESIPT fluorescence in solution, they exhibit an efficient, blue-shifted luminescence in the solid state. The luminescence quantum yield is 10 times larger compared to those observed in solution. Compounds 1, 4 and 5 are found to show two different solid-state luminescence according to different molecular packing. It is confirmed that those solid-state luminescence is controllable by thermal phase transition upon heating of powdered crystal.
