vestifmИзвестия Национальной академии наук Беларуси. Серия физико-математических наукProceedings of the National Academy of Sciences of Belarus. Physics and Mathematics Series1561-24302524-2415The Republican Unitary Enterprise Publishing House "Belaruskaya Navuka"10.29235/1561-2430-2021-57-2-224-231vestifm-589Research ArticleФИЗИКАPHYSICSПроявление динамики сверхбыстрых фотопроцессов в спектрах нестационарного поглощения растворов дифлавоноидаManifestation of the dynamics of ultrafast photoprocesses in the transient absorption spectra of diflavonoid solutionsТихомировС. А.TikhomirovS. A.

Тихомиров Сергей Александрович – член-корреспондент Национальной академии наук Беларуси, доктор физико-математических наук, главный научный сотрудник Центра фотоники атомных и молекулярных структур

пр. Независимости, 68-2, 220072, г. Минск, Республика Беларусь

Sergei A. Tikhomirov – Corresponding Member of the National Academy of Sciences of Belarus, Dr. Sc. (Physics and Mathematics), Chief Researcher of the Center of Photonics of Atoms and Molecules Structures

68-2, Nezavisimosti Ave., 220072, Minsk, Republic of Belarus

s.tik@dragon.bas-net.byИнститут физики им. Б. И. Степанова Национальной академии наук БеларусиB. I. Stepanov Institute of Physics of the National Academy of Sciences of Belarus202115072021572224231Copyright © Тихомиров С.А., 20212021Тихомиров С.А.Tikhomirov S.A.Данная работа распространяется под лицензией Creative Commons Attribution 4.0.This work is licensed under a Creative Commons Attribution 4.0 License.https://vestifm.belnauka.by/jour/article/view/589

C использованием метода фемтосекундной абсорбционной спектроскопии исследована динамика спектров нестационарного наведенного поглощения дифлавоноида 3,7-дигидрокси-2,8-ди(4-метоксифенил)-4Н,6Н-пирано[3,2-g]хромен-4,6-диона (ДФВ) в растворителях различной природы. Установлено, что трансформация нестационарных спектров ДФВ во времени обусловлена процессами внутримолекулярного переноса протонов в возбужденном синглетном состоянии. В неполярном растворителе толуоле реализуется перенос двух протонов в две стадии. Вначале за субпикосекундные времена из франк-кондоновского состояния образуется форма с одним перенесенным протоном. Далее из данного переходного состояния во временном диапазоне до 9 пс происходит перенос второго протона и формирование таутомера, обладающего высоким квантовым выходом флуоресценции ~0,66 и соответствующей полосой усиления в нестационарных спектрах наведенного поглощения. В полярном растворителе диметилформамиде в возбужденном состоянии за аналогичные, характерные для неполярного толуола, субпикосекундные времена образуется короткоживущая форма с одним перенесенным протоном и временем жизни порядка 25 пс. Полярность среды, влияющая на формирование набора «закрытых» и «открытых» форм ДФВ в основном состоянии, отличающихся различным относительным расположением в пространстве гидроксильных и карбонильных групп, и, соответственно, возможностями образования внутримолекулярных водородных связей, в значительной мере определяет механизм процесса внутримолекулярного переноса протонов в молекуле ДФВ. В неполярном растворителе реализуется последовательный перенос двух протонов с образованием флуоресцирующего долгоживущего таутомера, а в полярном происходит преимущественно перенос одного протона с образованием короткоживущей нефлуоресцирующей формы.

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.

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The authors declare that there are no conflicts of interest present.