CuO–CuAl2O4 and d-glucose catalyzed synthesis of a family of excited state intramolecular proton transfer imidazo[1,2-a]pyridine analogues and their optical properties

• CuO–CuAl2O4 composite and d-glucose catalyzed A3-coupling was developed.
• 2-Aryl-imidazo[1,2-a]pyridines displayed peculiar solvatochromic behaviour in chlorinated solvents.
• 2-(2′-Hydroxyphenyl) substituent underwent ESIPT process in non polar and polar solvents.
• Solid state ESIPT is desired factor for solid state lightening materials like OLEDs and lasers.

A simple and efficient route to luminescent imidazo[1,2-a]pyridines from 2-aminopyridines, phenylacetylene and arylaldehydes was achieved by an one-pot, tandem process starting with an A3-coupling followed by 5-exo-dig cyclization. Copper(II)oxide/copper aluminate composite (5 wt% CuO–CuAl2O4 composite) and d-glucose catalyzed optimal conditions for the reaction were established after examining various reaction parameters such as solvent, catalyst and temperature. The synthesis was much compatible with various functionalities. 2-Aryl-imidazo[1,2-a]pyridines not capable of excited state intramolecular proton transfer emission displayed moderate fluorescence quantum yields in the blue-green region due to intramolecular charge transfer process. In addition, they exhibited peculiar solvatochromic behaviour in chlorinated solvents like chloroform and dichloromethane. Products containing 2-(2′-hydroxyphenyl) substituent underwent excited state intramolecular proton transfer in non polar and polar-aprotic solvents. Although such type of emission in solvents was very weak, the Stokes shifts values were high (14,638–11,448 cm−1) with strong solid-state emission in green to yellow region.

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