Density functional theoretical investigation of intramolecular proton transfer mechanisms in the derivatives of 3-hydroxychromone

In this work, based on the density functional theory and time-dependent density functional theory methods, the properties of the 2 intramolecular hydrogen bonds (O1-H2···N3 and O4-H5···N6) of a new photochemical sensor 4-(3-thiazol-2-yl)-6tert-butyl phenol (Bis-HPBT) have been investigated in detail. The calculated dominating bond lengths and bond angles about these 2 hydrogen bonds (O1-H2···N3 and O4-H5···N6) demonstrate that the intramolecular hydrogen bonds should be strengthened in the S 1 state. In addition, the variations of hydrogen bonds of Bis-HPBT have been also testified based on infrared vibrational spectra. Our theoretical results reproduced absorption and emission spectra of the experiment, which verifies that the theoretical level we used is reasonable and effective in this work. Further, hydrogen bonding strengthening manifests the tendency of excited state intramolecular proton transfer (ESIPT) process.Frontier molecular orbitals depict the nature of electronically excited state and support the ESIPT reaction. According to the calculated results of potential energy curves along stepwise and synergetic O1-H2 and O4-H5 coordinates, the potential energy barrier of approximately 1.399 kcal/mol is discovered in the S 1 state, which supports the single ESIPT process along with 1 hydrogen bond of Bis-HPBT. In other words, the proton transfer reaction can be facilitated based on the electronic excitation effectively. In turn, through the process of radiative transition, the proton-transfer Bis-HPBT-SPT form regresses to the ground state with the fluorescence of 539 nm.

Section: Resultsmentioning

confidence: 99%

A theoretical study on the ESPT mechanism for a novel Bis‐HPBT fluorophore

Zhai

Zhang

Song

2018

“…In order to further understand the ESIPT mechanism, in this section, we adopt the manner of constructing potential energy curves because this method has been widely acknowledged . The potential energy curves are based on constrained optimizations in their relative electronic states along with keeping the O1‐H2 distances fixed in a series of values.…”

Section: Resultsmentioning

confidence: 99%

“…Then, the fast and strong reorganization of charge distribution resulted from the tautomerization makes these molecules very attractive towards the designs and applications such as laser dyes, LEDs, molecular switches, fluorescence sensors, and so forth . Herein, we want to mention that the understanding of ESIPT mechanism is a fundamental part of photochemistry, some fields of nanotechnologies, and some units of biological sensing as well …”

Section: Introductionmentioning

confidence: 99%

Theoretical insight into the excited‐state behavior of a novel Compound 1: A TDDFT investigation

Yang

Jia

et al. 2018

“…One of the most challenging problems in this field is the investigation of excited state hydrogen bonding interactions in molecules owning both proton acceptor and donor moieties . Therefore, the excited‐state dynamics of these hydrogen bonding molecules are usually complicated by the fact that multiple equilibrium and different species could appear.…”

Section: Introductionmentioning

confidence: 99%

Investigation on the excited state intramolecular proton transfer process for the novel 2‐(3,5‐dichloro‐2‐hydroxy‐phenyl)‐benzooxazole‐5‐carboxylicacid system

Gao

Yang

Zhang

et al. 2019

In view of the importance of excited state hydrogen bonding interactions and excited state proton transfer (ESPT) dynamical behaviors, in this work, we theoretically explore the excited state process for a novel 2‐(3,5‐dichloro‐2‐hydroxy‐phenyl)‐benzooxazole‐5‐carboxylicacid (DHPBC) system. On the basis of discrete Fourier transform (DFT) and time‐dependent density functional theory (TDDFT) methods, we reappear previous experimental reports with checking the reasonability of our theoretical level. We calculate and compare the primary geometrical parameters and hydrogen bonding energies around hydrogen bonding moieties, which reveals that the intramolecular hydrogen bond OH···N of DHPBC is enhanced in the S1 state. The increased electron densities around N atom contribute to attracting proton of hydroxyl upon the photoexcitation, which plays important roles in strengthening hydrogen bond and in facilitating excited state intra‐ or intermolecular proton transfer (ESIPT) process. Via constructing potential energy curves along with the ESIPT path, we verify that the ESIPT process of DHPBC system is ultrafast because of the low potential energy barrier. That should be the reason why the normal emission of DHPBC cannot be detected in previous experiment. This work not only clarifies the excited state hydrogen bonding interactions and fills the vacancy of specific ESIPT mechanism for DHPBC system in experiment, but also explains the fluorescence quenching phenomenon.