Photochemistry in rare-gas matrices:selected case studies

R. FAUSTO, I. REVA, GOMEZ ZAVAGLIA, ANDREA, A. KACZOR, E.M.S. MAÇÔAS, S. JARMELO, S. BREDA, A. BORBA, S. LOPES AND A.P. SIMÃO

Coimbra, Portugal

Congreso; 8th Photochemistry Meeting of the Portuguese Chemical Society; 2005

Sociedad Portuguesa de Quimica

Since its very beginning, matrix isolation has been recognized as an extremely powerful method in photochemistry [1]. In a matrix, molecular diffusion is precluded (except for some very small molecules) and, as a result, the complexity arisen from bimolecular processes can be avoided. Additionally, the very low work temperature makes thermally activated processes unimportant in most cases. On the whole, these characteristics usually reduce the accessible reaction channels, leading to a simplification of the photochemistry in a matrix, when compared to gaseous phase or solution. On the other hand, the main disadvantage is that recombination processes, involving fragments originated in a given molecule and that are produced in the same matrix cage, become more probable. In the less favorable cases, this may lead to suppression of reactivity for the matrix-isolated compound. In our laboratory we have been using matrix isolation connected with IR spectroscopy, as detection technique, to investigate both excited states (UV induced) and ground state (IR induced) photochemistry of a considerably large number of different chemical systems, of either industrial or biological importance. In the last 5 years, the group published ca. 80 papers using essentially this approach to the study of a large variety of chemical systems and chemical problems, from the dynamics of intramolecular energy relaxation to conformationally dependent photofragmentation, detection of exotic chemical species produced photochemically (e.g., antiaromatic diaziridines) or NIR induced conformational isomerization leading to production of conformers of simple organic molecules (e.g., acetic acid) never previously detected experimentally [2]. In this poster, some selected case studies recently undertaken in our laboratory will be presented. The main objective of this presentation is then to provide a general description of the capabilities of the technique in order to stimulate the interest of other research groups for possible collaborative work. References and Notes:      [1]        E. Whittle, D.A. Dows and G.C. Pimentel, J.Chem.Phys., 22 (1954) 1943.    [2]        A summary of the main activities of the research group can be found in the following webpage: http://www.qui.uc.pt/~rfausto/homepage/news.html   Acknowledgements: Credits shall also be given to our research partners from other Laboratories (Helsinki – M. Räsänen, Warsaw – M. Novak, Krakow – L. Proniewicz, Faro – Mª Lurdes Cristiano, Coimbra – E. Eusébio, S. Formosinho and L.G. Arnaut, Calcuta – N. Chattopadhay)