Molecular and supramolecular proton-transfer processes in 2(2′-hydroxyphenyl)-3H-imidazo[4,5-b]pyridine and its derivatives

2(2′-hydroxyphenyl)-3H-imidazo(4,5-b)pyridine, 2-HPIP, and its methylated derivatives belong to a class of molecules containing more than one set of proton donor–acceptor couples that may be coupled to one another. Consequently, 2-HPIP is found to form both π- and H-bound dimers in solutions and in the solid-state. In recent years, different 2-HPIP derivatives with various functional groups were prepared and structurally characterized. Their excited-state phototautomerization proton transfer processes in their different aggregation states were determined by studying their absorption and fluorescence spectra at different solvents at a wide range of concentrations.