Photoacidity as a tool to rationalize excited state intramolecular proton transfer reactivity in flavonols

Abstract

This work presents the determination of acidic strengths at the electronic ground and excited states (pK and ) of three flavonol derivatives using electronic absorption and fluorescence emission spectroscopy. The differences of the pK and values were successfully correlated with the molecular structures according to the substitution pattern at the flavonol structure (hydrogen, diethylamino or fluoro moieties). In order to obtain more information about the observed photoacidity of these superacids, geometry optimizations and excitation energy calculations were performed at the CAM-B3LYP/6-311++G(d,p) level for their neutral, protonated and deprotonated species.

Theoretical investigations on forward–backward ESIPT processes of three fluorophores deriving from 2-(2′-hydroxyphenyl)thiazole

“…In recent years, researchers proposed that the types of proton donor and proton acceptor could promote or hinder ESIPT process [29,[44][45][46][47][48]. Among ESIPT active molecules, phenols and naphthols are common photoacids since they have much lower acid dissociation constants in the excited state than that in the ground state (pK a * < pK a ) [49].…”

A Picosecond Time‐Resolved Spectroscopic Investigation of the Effect of pH on Morin Fluorescence

“…Finally, for a basic monohydroxyflavonol like 3HF, recent works proved that photodeactivation mechanism and chemical system were not so simple as it was firstly anticipated by Kasha. [13][14][15] Moreover, the dissociation of the hydroxyl group with the consequent formation of an anion was observed for 3HF both in ground [16] and in excited [17] state. Thus, this molecule can present four distinct emissions (from normal, tautomeric, anion and complex excited forms) depending on the medium (solvent, [18][19][20][21] pH [22] and bulk/confined [23][24][25] ) which differ in emission wavelengths and/or in lifetime of the excited species.…”

Modulating excited‐state intramolecular proton transfer of 2‐(5‐(4‐carboxyphenyl)‐2‐hydroxyphenyl)benzothiazole depending on substituents: A DFT/TD‐DFT study

“…[ 64–66 ] Therefore, 3HF derivatives with better photophysical characteristics have been widely researched theoretically and experimentally. [ 67–73 ] By chemical substitutions of electron‐donating groups at different substituted positions, all kinds of 3HF derivatives were obtained. Substituting furanyl, thiophenyl, and benzofuranyl for phenyl group at site 2 and introducing electron‐donating group at the site 4 made the enol absorption and keto emission spectra redshift, and fine‐regulated the ESIPT process, which led to increase the fluorescence intensity.…”