Revelation of ESIPT mechanism for the novel fluorescent system HNIBT in toluene and methanol solvents: A TDDFT study

Abstract

In this work, we devote to explore excited‐state intramolecular proton transfer (ESIPT) behavior for a novel fluorescent molecule naphthalimide‐based 2‐(2‐hydroxyphenyl)‐benzothiazole (HNIBT) [New J. Chem. 2019, 43, 9152.] in toluene and methanol (MeOH) solvents. Exploring weak interactions, stable HNIBT‐enol, and HNIBT‐MeOH‐enol complex can be found in S0 state via TDDFT/B3LYP/6‐311+G(d,p) level. Given photoexcitation, intramolecular hydrogen bond O1H2···N3 of HNIBT‐enol and HNIBT‐MeOH‐enol is dramatically enhanced, which offers impetus for facilitates ESIPT reaction. After repeated comparisons, we verify the unavailability of intermolecular hydrogen bonding effects between HNIBT‐enol and MeOH molecules. In view of excitation, HOMO (π) → LUMO (π*) transition and the changes of electronical densities indeed impulse ESIPT tendency. Via constructing potential energy curves (PECs), for both HNIBT‐enol and HNIBT‐MeOH‐enol complex, the ESIPT could only occur along with intramolecular hydrogen bond O1H2···N3. Through comparison, the potential barrier falls from 4.124 kcal/mol (HNIBT‐enol) to 2.132 kcal/mol (HNIBT‐MeOH‐enol). Therefore, we confirm that the ESIPT of the HNIBT system happens more easily in the MeOH solvent compared with the toluene solvent.

Electronic and photophysical properties of selected organic boron‐containing molecules: Insight into effects of heteroatom substitution and aggregation

“…Herein, the ground‐state geometries and related properties of the target organic diradical molecules were determined by the (U)B3LYP‐D3 approach, which has been widely validated in previous studies for PAHs. [ 58–63 ] Table 1 displays the relative free energies of different electronic structures of the studied molecules at the (U)B3LYP‐D3/6‐311G(d)/PCM level and the energy levels of the frontier molecular orbitals in the ground state. The predicted results indicate the open‐shell singlet state is generally the ground state for the four target molecules, although the Gibbs free energy difference between the open‐shell and closed‐shell singlet states is negligible.…”

“…Herein, the ground-state geometries and related properties of the target organic diradical molecules were determined by the (U)B3LYP-D3 approach, which has been widely validated in previous studies for PAHs. [58][59][60][61][62][63] 1. It could be noted that the cis molecules PHO2 and PHS2 have smaller singlet-triplet energy differences and narrower SOMO-LUMO gaps than the trans molecules PHO1 and PHS1, which matches the experimental results well.…”

Substituent effect on photophysical properties and proton transfer process of HBQ derivatives

“…In general, many factors can regulate ESIPT behavior, such as solvents, hydrogen bonding, and interactions with other molecules. The influence of these factors on ESIPT behavior has been discussed [23][24][25][26][27][28][29][30][31][32]. In recent years, many researchers have studied the effects of various substituents (such as -NO 2 , -COOH, or -CN) on the proton transfer process [33][34][35][36][37][38].…”