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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.

Photophysics of Lumichrome and Its Analogs

Sikorska E., Worrall D., Bourdelande J., Sikorski M.

Polish Journal of Chemistry

2003

Vol. 77 / nr 1

65-73

The spectroscopic and photophysical properties of lumichrome and its 1- and 3-methyl and 1,3-dimethyl derivatives in acetonitrile and in methanol are presented. In common with the parent molecule, the photophysics of the lumichrome methyl derivatives are dominated by non-radiative transitions in both methanol and acetonitrile. However, fluorescence yields in methanol are higher than in acetonitrile as a result of a reduction in the efficiency of non-radiative deactivation channels. These observations are discussed in terms of the available solvent-solute interactions.