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Spectroscopy and Photophysics of Lumiflavins and Lumichromes

Ewa Sikorska,*^† Igor V. Khmelinskii,^‡ Wiesław Prukała,^§ Siân L. Williams, Manisha Patel, David R. Worrall, Jose L. Bourdelande, Jacek Koput,^§ and Marek Sikorski*^§

Faculty of Commodity Science, Pozna University of Economics, al. Niepodlegloci 10, 60-967 Pozna, Poland, Universidade do Algarve, FCT, Campus de Gambelas, Faro 8000-117, Portugal, Faculty of Chemistry, A. Mickiewicz University, Grunwaldzka 6, 60-780 Pozna, Poland, Department of Chemistry, Loughborough University, Loughborough, Leicestershire LE11 3TU, UK, and Unitat de Qumica Orgnica, Universitat Autnoma de Barcelona, Bellaterra, Barcelona 08193, Spain

J. Phys. Chem. A, 2004, 108 (9), pp 1501–1508

DOI: 10.1021/jp037048u

Publication Date (Web): February 10, 2004

In papers with more than one author, the asterisk indicates the name of the author to whom inquiries about the paper should be addressed.

†

Address correspondence to this author at Poznań University of Economics. Fax: +48 61 8543993. Phone: +48 61 8569040. E-mail: ewa.sikorska@ae.poznan.pl.

‡

Universidade do Algarve.

A. Mickiewicz University. Fax: +48 61 8658008. Phone: +48 61 8291309. E-mail: sikorski@amu.edu.pl.

Loughborough University.

Universitat Autònoma de Barcelona.

Abstract

Solvent effects on the spectroscopic properties of lumichromes and lumiflavins are presented. Fluorescence yields for lumiflavins are an order of magnitude larger than those for lumichromes, due to their lower nonradiative rate constants. Solvent effects on the absorption and emission band positions are explained on the basis of hydrogen-bonding interactions. TD-DFT calculations predicted that the lowest energy states are n,π* in the case of lumichromes, but π,π* in the case of the lumiflavins. The overall consistency of the predicted singlet−singlet and triplet−triplet transitions obtained for the various compounds studied, and the good correspondence between the predicted and measured transitions, indicate that the techniques applied provide an accurate description of the spectral properties of lumiflavins and lumichromes. The measured singlet oxygen yields have shown the lumichromes to be efficient singlet oxygen sensitizers.

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