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Spectroscopy and Photophysics of 6,8-Dimethylalloxazine. Experimental and Theoretical Study

Sikorska E., Khmelinskii I., Bednarek A., Williams S., Worrall D., Herance J., Bourdelande J., Nowacka G., Koput J., Sikorski M.

Polish Journal of Chemistry

2004

Vol.78 /nr 11-12

2163-2173

Photophysics of 6,8-dimethylalloxazine was studied experimentally in function of solvent properties and theoretically by using time-dependent density functional theory (TD-DFT) calculations. The absorption spectrum of 6,8-dimethylalloxazine in the near-UV region shows one broad maximum at approximately 350 nm (ca. 28600 cm-1), which is a superposition of the two lowest-energy bands, and a fluorescence emission band varying from about 462 nm (21600 cm-1) in dioxane and acetonitrile to 475 nm (21000 cm-1) in methanol solution. In aprotic solvents neither band shows a significant dependence on the solvent polarity. The fluorescence lifetime increases in protic relative to aprotic solvents, and increases with increasing solvent polarity, due to reduction of the non-radiative rate constant. TD-DFT calculations provide details of the electronic structure of the molecule in its excited states and allow the interpretation of the observed photophysics in terms of the proximity effect.

An ab initio calculation of the vibrational spectrum of pyridine N-oxide and pyridine-d-5 N oxide

Szafran M., Koput J.

Polish Journal of Chemistry

1998

Vol. 72, nr 2

368-376

Density functional theory (using Becke's exchange and Lee-Young-Parr's correlation fanctionals (BLYP) and ab initio second-order Moller-Plesset (MP2) calculations were carried out in order to investigate the molecular structure and vibrational spectra of pyridine N-oxide and its perdeuterated analog. The calculated structural and spectral features are in good agreement with the available experimental results. Most of the BLYP/6-31G(d,p) and MP2/6-31G(d,p) non-CH stretching frequencies are slightly lower than the reliable experimental assignments; the mean deviations are 23 and 21 cm(-), respectively. On the basis of agreement between calculated and experimental results, assignments of the fundamental vibrational modes were examined and some reassignments were proposed.