Imidazo[1,5-a]pyridine-based derivatives as highly fluorescent dyes

This minireview collects the results that we obtained in the recent years on luminescent compounds based on imidazo[1,5-a]pyridines, an interesting class of heterocycles characterized by relevant photophysical properties like high Stokes shift, good absolute quantum yields, good photostability and a lambda(em) modulable depending on the substituents on the heterocyclic ring. These peculiar features can be transferred to the corresponding complexes when imidazo[1,5-a]pyridines are used as ligands. Herein we report on the photoluminescent behavior of zinc(II) and silver(I) complexes with 1-pyridylimidazo[1,5-a]pyridines acting as N,N-bidentate, neutral ligands. Then, zinc(II) and boron(III) compounds bearing N,O- monoanionic 2-(imidazo[1,5-a]pyridin-3-yl)phenolates will also be described. In all cases, a bright fluorescence emission was observed, either in the solid state or in solution; some promising derivatives showed a relevant photoluminescent behavior also when analyzed as thin films. A full spectroscopic characterization, combined with a theoretical approach (DFT), allowed to establish structure-properties relationships for the species investigated.