title: Octadecyl-viologen Photooxidation in Surface Films: Macroscopic Contraction of Langmuir Monolayer by UV Irradiation.
abstract: The effects of UV radiation on a viologen derivative, octadecylviologen (OV), in Langmuir monolayers at the air-aqueous solution interface and in Langmuir-Blodgett (LB) films have been investigated. Langmuir monolayers suffer a sharp contraction after UV irradiation, clearly visible by the drop in surface pressure or the loss of surface area observed in the surface pressure-area isotherms. The UV-vis reflection measurements reveal a deep change in the OV monolayer caused by a photochemical reaction, which suggests the pyridones formation as photoreaction products. LB films (Z type), before and after being irradiated with UV light, have been studied by using UV-vis absorption and infrared and X-ray photoelectron spectroscopy. The results confirm that after the photodegradation of the viologen films, the presence of oxygen results in the appearance of pyridones as reaction products. This article demonstrates that, in the absence of catalysts, the photooxidation of viologen surface films occurs only under a particular molecular organization imposed by the air-water interface.
authors.affiliation: Department of Physical Chemistry and Applied Thermodynamics, University of Córdoba , Campus Universitario de Rabanales, Edificio Marie Curie, Córdoba, Spain E-14014.
authors.forename: Jose M
authors.initials: JM
authors.lastname: Obrero-Pérez
authors.affiliation: Department of Physical Chemistry and Applied Thermodynamics, University of Córdoba , Campus Universitario de Rabanales, Edificio Marie Curie, Córdoba, Spain E-14014.
authors.forename: María T
authors.initials: MT
authors.lastname: Martín-Romero
authors.affiliation: Department of Physical Chemistry and Applied Thermodynamics, University of Córdoba , Campus Universitario de Rabanales, Edificio Marie Curie, Córdoba, Spain E-14014.
authors.forename: Marta
authors.initials: M
authors.lastname: Pérez-Morales
authors.affiliation: Department of Physical Chemistry and Applied Thermodynamics, University of Córdoba , Campus Universitario de Rabanales, Edificio Marie Curie, Córdoba, Spain E-14014.
authors.forename: Luis
authors.initials: L
authors.lastname: Camacho
authors.affiliation: Department of Physical Chemistry and Applied Thermodynamics, University of Córdoba , Campus Universitario de Rabanales, Edificio Marie Curie, Córdoba, Spain E-14014.
authors.forename: Eulogia
authors.initials: E
authors.lastname: Muñoz