Photophysical characterization of cinnamates
Artikel i vetenskaplig tidskrift, 2009

The photophysical properties of five methoxy-substituted 2-ethylhexylcinnamates were studied with experimental and theoretical methods. It was found that the fluorescence quantum yields varied strongly with the substitution pattern of the phenyl ring. A methoxy substitution at the meta position gave strong fluorescence, whereas the para substituted compounds were strongly quenched. This observation could be correlated to corresponding changes in the UV absorption spectra; the two lowest pi pi* states were split for the meta-methoxy substituted cinnamate but almost degenerate for the para compound. Semi-empirical quantum mechanical calculations confirmed both the observed state order and the difference in the experimentally determined activation energies for non-radiative decay. This "meta-effect" was also preserved in the trimethoxy-substituted compounds, 2-ethylhexyl-2,4,5- and 2,4,6-trimethoxycinnamate, resulting in strong fluorescence and relatively high barrier for non-radiative decay in the former and weak fluorescence and relatively low barrier for non-radiative decay in the latter. The obtained information shows how the performance of the commercial sunscreen agent, 2-ethylhexyl-para-methoxycinnamate (OMC) might be improved.

meta

molecules

photoisomerization

esters

photochemistry

Författare

T. M. Karpkird

Kasetsart University

S. Wanichweacharungruang

Chulalongkorn University

Bo Albinsson

Chalmers, Kemi- och bioteknik, Fysikalisk kemi

Photochemical and Photobiological Sciences

1474-905X (ISSN) 1474-9092 (eISSN)

Vol. 8 1455-1460

Ämneskategorier

Fysikalisk kemi

Kemi

DOI

10.1039/b909695g