One pot synthesis of low cost emitters with large Stokes' shift

A series of 1,3-diarylated imidazo[1,5-a]pyridine derivatives were synthesized in high yields by a one-pot, three components, condensation of phenyl(pyridin-2-yl)methanone with several aldehydes in the presence of ammonium acetate. These compounds were characterized by spectroscopic and crystallographic techniques and their optical properties were discussed in relation to their chemical structures. Absorption and fluorescence spectra generally show two absorption maxima around 310 nm and 350 nm and an emission maximum between 460 and 550 nm with a remarkable Stokes' shift range of 90–166 nm. Moreover, depending on the chemical structure of the substituent in position 3, we were able to tune the quantum yields (Φ) in solution from 6.4% to 38.5%. Finally, the 1-phenylimidazo[1,5-a]pyridine substituted with a 3-(2-methoxyphenyl) group (large Stokes' shift, high Φ) was dispersed in a transparent thermosetting polyurethane resin giving a luminescent low cost material.