Fluorescent trifluoromethylated imidazo[1,5-a]pyridines and their application in luminescent down-shifting conversion

In the last few years, imidazo[1,5-a]pyridine derivatives have attracted growing attention due to their unique optical behaviours. Herein, a series of trifluoromethylated substituted imidazo[1,5-a]pyridine derivatives were synthesized and their optical properties investigated. Depending on the position of the trifluoromethylated substituents on the imidazo[1,5-a]pyridine nucleus, we were able to tune the quantum yields (Φ) both in acetonitrile solution (from 13% to 39%) and in the polymeric matrix (10%–58%) with a remarkable large Stokes shift. The investigated fluorophores were dispersed in a transparent polyurethane resin, providing a possible luminescent low-cost material for down-shifting conversion. An analysis based on the chemical structures and spectroscopic data, both in solution and polymeric medium, is reported to address the best strategies to optimize the photophysical properties and prevent aggregation. Finally, optimized polyurethane-based films prepared with compounds 2 and 3 were tested as a luminescent coating on a commercial photodiode, enabling their technological application.