Opening 2,2-diphenyl-2H-chromene to infrared light.

Time-resolved vibrational spectroscopy studies are reported on the photoinduced structural dynamics of 2,2-diphenyl-2H-chromene, a prototypical photochromic compound that undergoes ring opening upon UV radiation. The transient IR absorption measurements in combination with (TD-)DFT calculations have been used to understand in detail the life cycle of such compounds. Excited-state decay and ring opening was found to occur on an ultrafast time scale. Three species have been identified in the time-resolved IR spectra with two short-lived species (on a picosecond timescale) and a final long-lived species that remains after the measurable ns delay range. These species have been assigned to various open isomers using quantum chemical calculations of equilibrium structures and force fields. From the experiments and calculations key conclusions can be drawn on previously suggested models for the photocycle of such compounds, as well as on possible ways to controllably influence the performance of these compounds.