Characterization of photophysical and photochemical properties of 2-ethyl-hexyl 4 ?methoxycinamate isomers. Influence of sunscreens on quenching of singlet molecular oxygen.

CÉSAR N. PEGORARO; STELLA M. CHIACCHIERA ; WATER A. MASSAD; CARLOS PREVITALI; CARLOS A. CHESTA; MALISA S. CHIAPPERO; HERNÁN A. MONTEJANO

Carlos Paz

Conferencia; 13th Latin American Conference on Physical Organic Chemistry; 2015

CHARACTERIZATION OF PHOTOPHYSICAL AND PHOTOCHEMICALPROPERTIES OF 2-ETHYL-HEXYL 4 ?METHOXYCINAMATE ISOMERS.INFLUENCE OF SUNSCREENS ON QUENCHING OF SINGLET MOLECULAROXYGEN122221Pegoraro C , Chiacchiera S , Massad W , Previtali C , Chesta C , Chiappero M and Montejano H2(1) Departamento de Química - Facultad de Ciencias Exactas y Naturales, UniversidadNacional de Mar del Plata (UNMdP)(2) Departamento de Química- Ciencias Exactas, Físico-Químicas y Naturales, UniversidadNacional de Río Cuarto (UNRC)The development and evaluation of sunscreens is important because UVA and UVBsunlight can penetrate deep into human skin and cause severe internal damage, besides erythemaand photoaging. Although in the literature it is amply documented the photodegradation and theeffect of the photoproducts of many molecules employed as sunscreens, several aspects of thephotophysical and photochemical behavior of these molecules are not totally elucidated.Here we present a detailed study of the photophysics and photochemistry of 2-ethylhexyl 4?methoxycinamate a molecule that has frequently present in commercial sunscreens. The main effectof UV irradiation of E-2-ethylhexyl 4?methoxycinamate (E) is trans/cis photoisomerizaton to form theZ isomer Z-2-ethylhexyl 4?methoxycinamate (Z). This process is reversible and it is the predominantdecay route of the electronic excited states of E and Z, and therefore, the fluorescence and tripletyields are extremely low, as required for an efficient sunscreen. However, when the molecule isimmobilized in an organized medium, the fluorescence is present and can be characterized by staticand dynamic experiments. To this end we conducted fluorescence experiments in a poly methylmethacrylate matrix (p-MMA).We also performed studies on the irradiation of E with a high dose of UV. It was found that aphotocomsuption of E takes place through a second order reaction. New photoproducts with a lowextinction coefficient are formed which were in part indentified by means of HPLC-MS/MS. Thisreaction does not occur by thermal activation.The possibility of generation of reactive oxygen species by E/Z (and their photoproducts)was also investigated. It was found that while singlet oxygen is not form both isomers quench the1phosphorescence of O 2 . The efficiency of the E isomer for this process is twice that of the Z isomer.