Solvent‐polarity‐dependent excited‐state behaviors for 2‐(2‐hydroxyphenyl) benzothiazole‐5‐(9H‐carbazol‐9‐yl)phenol fluorophore: A theoretical study

Abstract

In this work, we mainly focus on elaborating the effects of solvent polarity on excited state interactions and intramolecular proton transfer (ESIPT) behavior for the novel dye 2‐(2‐hydroxyphenyl) benzothiazole‐5‐(9H‐carbazol‐9‐yl)phenol (HBT‐Cz). Six aprotic solvents with different polarities are considered. Via comparing geometrical parameters, infrared (IR) vibrational spectra, and atomic charge distributions, we confirm that the hydrogen bond of HBT‐Cz is enhanced in S1 state. The enhancement of hydrogen bonding with low polarity is particularly important. Via exploring molecular orbitals, we find that intramolecular charge transfer happens and charge redistribution facilitates ESIPT reaction. Results show that low solvent polarity is more conducive to ESIPT process for HBT‐Cz. In order to clarify detailed reaction mechanism, we construct potential energy curves and determine that the ESIPT process of HBT‐Cz fluorophores could be controlled by solvent polarity. We not only elucidate the excited state behavior of HBT‐Cz systems but also present the polarity‐dependent ESIPT mechanism for HBT‐Cz fluorophore.

Computational Investigation about the Effects of Solvent Polarity and Chalcogen Element Electronegativity on ESIPT Behaviors for the Et2N-Substituted Flavonoid

“…To quantitatively depict the reaction processes and barriers in these states, we investigate the behaviors of ESIPT reactions by constructing potential energy surfaces (PESs). It is well recognized that PESs pose challenges to normal chemical reactions in excited states due to one or more geometric changes [13,18,[30][31][32][33]. Regarding the hydrogen bond, the O1-H2•••O3 interaction can be classified as a five-membered ring type.…”

“…The determination of reaction processes and barriers in excited states can be achieved quantitatively by constructing PECs through a restrictive optimization approach, thereby facilitating the investigation of ESIPT reaction behaviors. It is widely acknowledged that PECs present challenges to conventional chemical reactions in excited states due to one or more alterations in geometry [13,18,[30][31][32][33]. By employing a rigorous optimization method, we successfully constructed PECs while preserving an elongated O1-H2 bond distance ranging from 0.90 Å to 2.20 Å in increments of 0.05 Å, encompassing all photoinduced configurations (as illustrated in Figure 8).…”

“…Due to the different charge recombination behavior of the reactants and products in ESIPT reactions, the double fluorescence phenomenon and large Stokes shift have also become the signature phenomena of ESIPT reactions [13][14][15]. Just due to the unique luminescent property of ESIPT, many potential applications already involve this reaction, such as molecular switches, fluorescent sensors, LEDs, and so on [16][17][18][19][20].…”