Photoexcited Singlet and Triplet States of a UV Absorber Ethylhexyl Methoxycrylene

The excited states of UV absorber, ethylhexyl methoxycrylene ( EHMCR ) have been studied through measurements of UV absorption, fluorescence, phosphorescence and electron paramagnetic resonance (EPR) spectra in ethanol. The energy levels of the lowest excited singlet (S 1 ) and triplet (T 1 ) states of EHMCR were determined. The energy levels of the S 1 and T 1 states of EHMCR are much lower than those of photolabile 4‐ tert ‐butyl‐4′‐methoxydibenzoylmethane. The energy levels of the S 1 and T 1 states of EHMCR are lower than those of octyl methoxycinnamate. The weak phosphorescence and EPR B min signals were observed and the lifetime was estimated to be 93 ms. These facts suggest that the significant proportion of the S 1 molecules undergoes intersystem crossing to the T 1 state, and the deactivation process from the T 1 state is predominantly radiationless. The photostability of EHMCR arises from the 3 ππ* character in the T 1 state. The zero‐field splitting (ZFS) parameter in the T 1 state is D ** = 0.113 cm −1 .