Open AccessManifestation of the dynamics of ultrafast photoprocesses in the transient absorption spectra of diflavonoid solutions
Author(s) -
С. А. Тихомиров
Publication year - 2021
Publication title -
vescì nacyânalʹnaj akadèmìì navuk belarusì. seryâ fìzìka-matèmatyčnyh navuk
Language(s) - English
Resource type - Journals
eISSN - 2524-2415
pISSN - 1561-2430
DOI - 10.29235/1561-2430-2021-57-2-224-231
Subject(s) - ultrafast laser spectroscopy , photochemistry , chemistry , intramolecular force , absorption spectroscopy , tautomer , absorption (acoustics) , proton , picosecond , spectroscopy , excited state , singlet state , quantum yield , solvent , spectral line , fluorescence , atomic physics , materials science , stereochemistry , organic chemistry , optics , laser , physics , quantum mechanics , astronomy , composite material
Herein, using the femtosecond absorption spectroscopy method, the dynamics of the nonstationary induced absorption spectra of diflavonoid 3,7-dihydroxy-2,8-di(4-methoxyphenyl)-4H, 6H-pyrano[3,2-g]chromene-4,6-dione (DFV) in solvents of different polarities is studied. It is found that the rapid transformation of the transient absorption spectra of DFV in time is due to the processes of intramolecular protons transfer in excited singlet states. For a nonpolar solvent, two protons are transferred in two stages. Initially, during the sub-picosecond times, a form with a single transferred proton is formed from the Frank-Condon state. From this transition state, in a time range of about 9 ps, the second proton is transferred and the two proton transfer tautomer with a high quantum yield of fluorescence ~0.66 is formed, which has the gain band in the transient absorption spectra. For the polar solvent dimethylformamide only the short-lived form with a single proton transferred is formed also during the subpicosecond times practically the same ones as for the nonpolar solution and has a lifetime of about 20 ps. The polarity of the medium, which affects the formation of a set of the “closed” and “open” forms of DFV in the ground state, differing in relative positions in the space of hydroxyl and carbonyl groups, largely determines the mechanism of the intramolecular proton transfer process in the DFV molecule, which consists in the sequential transfer of two protons in a non-polar solvent to form a fluorescent long-lived tautomer and the transfer of one proton in polar solvents to form a short-lived non-fluorescent form.