Electronic structures and population dynamics of excited states of xanthione and its derivatives

- A methoxy derivative of xantione was synthesized its spectra were measured.
- Time constants of S2→S1 and S1→T1 transitions are determined.
- Attachment of methoxy groups to xantione increases the S2 state lifetime.

A new compound, 1,3-dimethoxy xanthione (DXT), has been synthesized and its absorption (stationary and transient) and luminescence spectra have been measured in n-hexane and compared with xanthione (XT) spectra. The pronounced broadening of xanthione vibronic absorption band related to the electronic transition to the second singlet excited state has been observed. Distinctions between the spectra of xanthione and its methoxy derivatives are discussed. Quantum chemical calculations of these compounds in the ground and excited electronic states have been accomplished to clarify the nature of electronic spectra changes due to modification of xanthione by methoxy groups. Appearance of a new absorption band of DXT caused by symmetry changes has been discussed. Calculations of the second excited state structure of xanthione and its methoxy derivatives confirm noticeable charge transfer (about 0.1 of the charge of an electron) from the methoxy group to thiocarbonyl group. Fitting of the transient spectra of XT and DXT has been fulfilled and the time constants of internal conversion S2→S1 and intersystem crossing S1→T1 have been determined. A considerable difference between the time constants of internal conversion S2→S1 in XT and DXT is uncovered.

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