Anion–π interactions in new electron-deficient π systems: the relevance to solid phosphorescent colors

Abstract

We herein report a new electron-deficient π system, namely carboxycarbonyl substituted imidazo[1,2-a]pyridinium, which exhibits various noncovalent interactions (hydrogen bonding, anion–π and η¹-type anion–π) with chloride or perchlorate anion. Crystallographic results demonstrate that the interaction types of chloride anion and π receptor systems can be tuned: from anion–π interactions (with guest methanol molecule in crystal) to η¹-type anion–π interactions (without guest methanol molecule in crystal). These carboxycarbonyl substituted imidazo[1,2-a]pyridinium salts also exhibit different phosphorescent colors in the solid state induced by crystal stacking structures or anion–π interactions that can influence the charge transfer to electron-deficient carboxycarbonyl substituted imidazo[1,2-a]pyridinium. Especially, the solid phosphorescent color changes induced by anion–π interactions are very interesting. The high solubility in water makes these purely organic phosphorescent materials promising candidates for potential applications.