GOMEZ ZAVAGLIA Andrea
Photochemistry of Tetrazole Derivatives in Cryogenic Rare Gas Matrices
A. GÓMEZ-ZAVAGLIA, I.D. REVA, L.M.T. FRIJA, M.L.S. CRISTIANO AND R. FAUSTO
Chemical Physics Research Journal
Nova Science Publishers
Lugar: New York, USA; Año: 2009 vol. 1 p. 221 - 250
A general overview of the photochemistry of tetrazoles and the general pattern of their photoreactions is presented. The application of tetrazoles in agriculture and medicine is widespread and well-known. In many drugs and drug-candidates, replacement of carboxylic acid groups, −COOH, by tetrazolic acid fragments, −CN4H, is frequent, resulting in an increase in bioavailability and potency of the pharmacophore. Tetrazoles also have many other applications, such as in photography and photoimaging, and in automobile industry as gas generating agents for airbags. These compounds also exhibit a very rich photochemistry, which is strongly influenced by the substituents present in the tetrazolic ring. Several representative tetrazoles were trapped in a rigid environment of solidified noble gases (argon, xenon) at cryogenic temperatures (typically 10 K) and subjected to in situ photolysis. The range of possible rearrangements of the isolated species was controlled by choice of the excitation wavelengths. FT-IR spectroscopy provided experimental frequencies and intensities of characteristic absorptions of the isolated chemical species, both for reagents and photoproducts. The analysis of experimental data was assisted by their direct comparison with the vibrational spectra theoretically calculated for the single molecule in vacuum. This comparison was facilitated because the inert matrix only slightly affects the structure of the isolated molecules, and also owing to the high resolution of infrared matrix spectra (a few tenths UV-excitation resulted in photofragmentation of the monomeric tetrazoles with a wide range of exit channels. Since the obtained fragments in general stay in the matrix cage where they are formed, no subsequent cross-reactions involving species resulting from photolysis of different reactant molecules can occur, strongly reducing the number of possible photoproducts in comparison with gas phase or solution studies. This fact introduced a useful simplification for the interpretation of the reaction mechanisms. A number of relatively unusual or highly reactive molecules, such as antiaromatic azirines, azides, isocyanates or isothiocyanates, may be formed from photolysis of tetrazoles in a matrix. In some examples described in this Chapter, the spectroscopic characterization of these molecular species was presented for the first time.