Investigation of excited-state proton transfer in 3-hydroxyflavone molecules |
| |
Authors: | V I Tomin |
| |
Institution: | (1) Physical Chemistry Department, Indian Association for the Cultivation of Science, Jadavpur, Kolkata, 700 032, India; |
| |
Abstract: | The dual fluorescence spectra of 3-hydroxyflavone molecules excited by electromagnetic radiation in the region of the S
1 and S
2 absorption bands in the temperature region of 20–80°C are studied using the dynamic quenching of the excited state. An analysis
of the fluorescence parameters shows that heating the solution from room temperature to 60°C increases the proton transfer
rate by a factor of 1.24 in the case of standard excitation into the main absorption band and even stronger (by a factor of
6.9) in the case of excitation into the second absorption band. The presence of a quencher reduces the yield of the two emission
bands and noticeably increases the proton transfer rate, by a factor of 1.16 at room temperature and by a factor of 1.25 at
80°C. Upon excitation into the second singlet band, the transfer rate increases even more (especially at higher temperatures),
by a factors of 1.24 and 3.5 for the same temperatures. The temperature dependences of the transfer rate constant allowed
us to estimate the activation energies of the proton transfer reaction under different physical conditions and reach conclusions
about the mechanism by which this reaction proceeds. It is found that the proton transfer activation energy decreases from
500 to 360 cm−1 when measured in temperature ranges of 20–40 and 20–60°C. The introduction of a quencher with a concentration of 5 × 10−3 M increases the activation barrier to 534 and 471 cm−1 in the same temperature ranges. |
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|