Stepwise Excited-state Double Proton Transfer and Fluorescence Decay Analysis

Abstract

This work considers excited state intramolecular proton transfers (ESIPT) occurred in multiple hydroxyl-containing compounds with one proton transfer site in the normal form. If several hydroxyl groups are located close to each other in a molecule, then the ESIPT process can lead to the next one. A proton donor site in the first ESIPT will be a proton acceptor during the second reaction. Therefore, a number of consecutive excited state proton transfers can occur. This work deals with the case of two successive proton transfers occurred in the molecular system. Such process is called as a stepwise excited state intramolecular double proton transfer (stepwise ESIDPT). It leads to the formation of two molecular tautomers. Therefore, fluorescence of such compounds can contain different emission bands correspond to emission of normal form and two tautomers. In this work, a rigorous analysis of fluorescence decay kinetics has been made using the model with three species, including a normal molecular form and two tautomers. The work presents theoretical framework of fluorescence decay analysis of ESIDPT process taking into account three species emission. Theoretically, the stepwise proton transfers can be consisted of more than two ESIPT reactions. It depends on molecular structure and number of involved hydroxyl groups. Here, a formal analysis of fluorescence decay kinetics has been made in the case of a stepwise process consisting of two proton transfers. Moreover, the quantum-chemical calculations have been performed in the case of scutellarein. It is a multiple hydroxyl-containing flavone and, therefore, it can be applied as a model molecule to study stepwise intramolecular proton transfers. The hypothetical scheme of ESIDPT has been proposed for this compound. Graphical abstract

Diffusion flames and a semi-empirical method for estimating the distribution of hydrogen molecules in propane flames

“…Kinetic analysis of the results for reactions (3) and (4) showed satisfactory agreement with experimental data and the rate constants of these reactions 2•1010 and 8•109 l 2 /mol 2 s, respectively, were obtained [21]. At present, the absorption spectroscopy method based on the phenomenon of selective absorption of radiation by gases is widely used [23; 24].…”

“…Since sodium atoms have low electronic levels, only a portion of the recombination heat released by the reaction is sufficient to excite them, and the presence of low-lying ionic terms increases the probability of energy transfer between them. Several are known to explain the coloring of hydrogen-burning flames by the addition of sodium atoms and the addition of sodium to the stream of hydrogen atoms coming out of the electric discharge tube [20][21][22]. Two elementary acts leading to the manifestation of excited sodium atoms are considered:…”

Feasibility of multiple excited-state proton transfer processes in hydroxyquinoline-containing benzobisimidazole dyes

“…Excited-state double proton transfer (ESDPT) constitutes an even more interesting phenomenon because two protons can be translocated within the same molecular structure, either by a synchronous or asynchronous mechanism. 38–47 As an example, a simple compound such as [2,2′-bipyridyl]-3,3′-diol shows photoexcited double proton transfer with emission bands at 510 and 568 nm related to the diketo and monoketo forms. 39,48 Experimental and theoretical studies indicated that the most likely mechanism is a sequential proton transfer.…”