A detailed theoretical simulation about the excited state dynamical process for the novel (benzo[d]thiazol‐2‐yl)‐5‐(9H‐carbazol‐9‐yl)phenol molecule

Abstract

Given that molecular excited state dynamical process plays important roles in designing and developing novel applications in recent years. In this work, based on density functional theory (DFT) and time‐dependent density functional theory (TDDFT) methods, we theoretically explored the novel (benzo[d]thiazol‐2‐yl)‐5‐(9H‐carbazol‐9‐yl)phenol (HBT‐Cz) system about its excited state behaviors. Via simulating the electrostatic potential surface (EPS) of HBT‐Cz structure, we confirm the formation of intramolecular hydrogen bond O2—H3···N4 in the S0 state. Our theoretical dominating bond lengths, bond angles, and the infrared (IR) vibrational spectra involved in hydrogen bond demonstrate that O2—H3···N4 should be strengthened in the S1 state. Upon the photoexcitation, we find the charge transfer characteristics around hydrogen bonding moieties play important roles in facilitating excited state intramolecular proton transfer (ESIPT) process. Via constructing potential energy curves, we confirm the ESIPT reaction that further explains previous experimental phenomenon. Moreover, we also search the S1‐state transition state (TS) structure along with ESIPT path, based on which we simulate the intrinsic reaction coordinate (IRC) path. Combing with the atom‐centered density matrix propagation (ADMP) molecular dynamics simulation, we further confirm the ESIPT mechanism presented in this work. We sincerely hope that our theoretical work could guide novel applications based on HBT‐Cz system in future.

Amplified Spontaneous Emission from Zwitterionic Excited-State Intramolecular Proton Transfer

“…The shortening of the hydrogen-bond length in the E-S 1 states indicates that the N center has more affinity toward the proton in the excited state, which would lead to ESIPT. The N···H bond lengths calculated in both HBT-Fl1 and HBT-Fl2 for S 0 and S 1 states of E form are comparable to ones previously reported for other HBT derivatives . In both cases, the E-S 1 state corresponds to the π–π* excitation of an electron from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO).…”

“…The photophysical properties of ESIPT dyes in different solvents can often provide vital information regarding the activation energy required to achieve intramolecular proton transfer. , Previous theoretical studies have shown that hydrogen bonding between nitrogen and hydrogen can promote the ESIPT process . Solvent reorganization accompanies hydrogen bonding between the dye and the solvent molecules. ,, This can further induce an external barrier to the proton transfer, which, in addition to the intrinsic enol–keto energy barrier, may lead to dual emission from both enol and keto species.…”

“…47,48 Previous theoretical studies have shown that hydrogen bonding between nitrogen and hydrogen can promote the ESIPT process. 49 Solvent reorganization accompanies hydrogen bonding between the dye and the solvent molecules. 33,50,51 This can further induce an external barrier to the proton transfer, which, in addition to the intrinsic enol− keto energy barrier, may lead to dual emission from both enol and keto species.…”

“…The N•••H bond lengths calculated in both HBT-Fl1 and HBT-Fl2 for S 0 and S 1 states of E form are comparable to ones previously reported for other HBT derivatives. 49 In both cases, the E-S 1 state corresponds to the π−π* excitation of an electron from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO). The HOMO is mainly located on the HP and fluorene moieties for both HBT-Fl1 and HBT-Fl2 (Figure S10).…”