Abstract :
We present a systematic study of spectroscopy and photophysics of 9-methylalloxazine using experimental and theoretical approaches.
Fluorescence lifetimes and quantum yields were measured in a range of solvents. The singlet state decay is dominated by non-radiative
processes. The non-radiative relaxation rate and the radiative rate undergo notable changes when going from non-polar solvents to polar and
hydrogen-donor solvents, due to the level inversion phenomena: the lowest excited state is of the n;p* character in non-polar solvents, and of
the p;p* character in hydrogen-donor solvents.
The S0 ! Sn and the T1 !Tn absorption spectra were calculated, using the TD-DFT ab initio approach. The theoretical results for this and
other similar molecules demonstrate an overall consistency and reproduce the experimental spectra quite well. The calculations confirmed
the existence of a weak n;p* absorption band close to each of the two lowest-energy p;p* bands, of low oscillator strength and thus not
observable in the absorption spectra. The remaining difference between experimental and calculated absorption bands, of 1000–2000 cm21,
was attributed to the condensed-phase intermolecular interactions, disregarded in the present calculations, made for isolated molecules.
The singlet oxygen emission measurements demonstrated that 9-methylalloxazine is an efficient singlet oxygen sensitizer, especially in
non-polar solvents.
q 2004 Elsevier B.V. All rights reserved.
