Cisoid-cis intermediate plays a crucial role in decolouration rate in photochromic reaction of 8H-pyranoquinazolines and 3H-naphthopyrans

The photochromic reaction of 8H-pyranoquinazoline shows intriguing aspects in comparison to 3H-naphthopyrans. These come from a stabilized excited singlet state for 8 H-pyranoquinazoline, which has a longer lifetime and is strongly sensitive to the solvent. The polar solvent acetonitrile reduces the quantum yield of coloured isomer formation (transoid-cis species). Colour fading related to the decay of transoid-cis population is faster than that for 3H-naphthopyran family and occurs within few seconds time-window in solution at room temperature. Theoretical calculations show the crucial role in fading process played by the potential energy landscape, with the cisoid-cis intermediate located in a shallow high-energy minimum.

Automated summary

The photochromic reaction of 8H-pyranoquinazoline has unique characteristics compared to 3H-naphthopyrans. The stabilized excited singlet state of 8H-pyranoquinazoline has a longer lifetime and is highly sensitive to solvents. The polar solvent acetonitrile reduces the quantum yield of the colored isomer formation. The color fading related to the decay of the transoid-cis population in 8H-pyranoquinazoline is faster compared to the 3H-naphthopyran family.