Proton Transfer in 3-Hydroxyflavone: The Influence of Physical Excitation Conditions and Dynamic Quenching

The influence of excitation conditions, temperature, and fluorescence quencher on the properties of 3-hydoxyflavone excited states is considered. Two-band fluorescence spectra of 3-hydroxyflavone formed in excitation by electromagnetic radiation in the region of the S(1) and S(2) absorption bands over the temperature range 20-80 degrees C were recorded and analyzed. The TEMPO spin quencher was used as an excited state quencher. An analysis of the fluorescence parameters showed that solution heating from room temperature to 60 degrees C increased the rate of proton transfer by 1.24 times at standard excitation into the main absorption band. The rate increased still more rapidly (by 6.9 times) in excitation into the second absorption band. The presence of the quencher caused a decrease in the yields of both fluorescence bands according to the diffusion mechanism and a noticeable growth in the rate of proton transfer. The latter increased by 1.16 times at room temperature and by 1.25 times at 80 degrees C. The corresponding changes were more substantial, especially at elevated temperatures, if the second singlet band was excited. They then amounted to 1.24 and 3.5 times over the same temperature range.