Excited Triplet State of a UV-B Absorber, Octyl Methoxycinnamate

Abstract

The lowest excited triplet (T1) state of the most widely used UV-B absorber, octyl methoxycinnamate (OMC), has been studied through measurements of phosphorescence and electron paramagnetic resonance spectra in rigid solutions at 77 K. The energy level and lifetime of the T1 state of OMC were determined. The observed T1 lifetime and zero-field splitting parameter suggest that OMC possesses mainly a 3ππ* character in the T1 state.

Photoexcited Singlet and Triplet States of a UV Absorber Ethylhexyl Methoxycrylene

“…As the observed D ** value of EHMCR is fairly smaller than those of methoxyphenyl, tolyl, ethylenic and carbonyl fragments, the two unpaired electrons localize on neither the methoxyphenyl, nor the tolyl, nor the ethylenic, nor the carbonyl fragment. The delocalized character of the unpaired electrons has been reported for some UV absorbers, such as OMC, 2‐methylphenyl 4‐methoxycinnamate, dioctyl 4‐methoxybenzylidenemalonate and BMDBM . On the other hand, the EPR B min signal of the T 1 state of OCR is too weak to be observed.…”

“…(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21) It is important to study how each UV absorber in the mixture behaves under UV irradiation. Therefore, it is especially important to determine the energy levels of the lowest excited singlet (S1) and triplet (T1) states of individual UV absorbers (22)(23)(24)(25) and discuss the nature of the photoexcited states of UV absorbers and their deactivation processes.…”

Photoexcited States of UV Absorbers, Benzophenone Derivatives

“…As is clearly seen in Table that the T 1 energies of the BP derivatives studied are ~24 500 cm −1 . The T 1 energies of the BP derivatives studied are higher than those of the most widely used representative of UV‐A absorber, 4‐ tert ‐butyl‐4′‐methoxydibenzoylmethane (BMDBM, Avobenzone, Parsol 1789) and the most widely used representative of UV‐B absorber, octyl methoxycinnamate (OMC, 2‐ethylhexyl 4‐methoxycinnamate, Octinoxate, Parsol MCX) . These BP derivatives may act as triplet energy donors for BMDBM and OMC in the mixtures of UV absorbers.…”

Energy-donor phosphorescence quenching study of triplet–triplet energy transfer between UV absorbers

“…1, BMDBM is excited mainly through the excitation at 355 nm (28,200 cm À 1 ) and at 365 nm (27,400 cm À 1 ). The energy levels of the lowest excited singlet (S 1 ) states of BMDBM (enol form), OMC and DOMBM have been reported to be 25,600 cm À 1 , 29,900 cm À 1 and 29,100 cm À 1 , respectively [30,34,35]. The energy levels of the S 1 states of these UV absorbers were estimated from the intersection point of the UV absorption and fluorescence spectra [36].…”

“…As a result, the efficacy of OMC as a UV-B absorber decreases under UV irradiation. The quantum yield of S 1 -T 1 intersystem crossing (ISC) of OMC is small [35]. In the mixture of BMDBM-OMC, the triplet OMC molecules are generated by photosensitization with BMDBM and OMC undergoes photoisomerization through both the S 1 and T 1 states.…”