Theoretical Insights on Solvent Control of Intramolecular and Intermolecular Proton Transfer of 2-(2′-Hydroxyphenyl)benzimidazole

Abstract

Excited-state proton transfer (ESPT) processes of 2-(2'-hydroxyphenyl)benzimidazole (HBI) and its complexation with protic solvents (HO, CHOH, and NH) have been investigated by both static calculations and dynamics simulations using density functional theory (DFT) at B3LYP/TZVP theoretical level for ground state (S) and time-dependent (TD)-DFT at TD-B3LYP/TZVP for excited state (S). For static calculations, absorption and emission spectra, infrared (IR) vibrational spectra of O-H mode, frontier molecular orbitals (MOs), and potential energy curves (PECs) of proton transfer coordinate were analyzed. Simulated absorption and emission spectra show an agreement with available experimental data. The hydrogen bond strengthening in the S state has been proved by the changes of IR vibrational spectra and bond parameters of the hydrogen moiety with those of the S state. The MOs provide the visual electron density redistribution confirming the hydrogen bond strengthening mechanism. The PECs show that the proton transfer (PT) process is easier to occur in the S state than the S state. Moreover, on-the-fly dynamics simulations of all systems were carried out to provide the detailed information on time revolution. The results revealed that the excited-state intermolecular proton transfer for HBI is fast, whereas the excited-state intermolecular proton transfer for HBI with protic solvents are slower than that of HBI because the competition between intra- and intermolecular hydrogen-bonds between HBI and protic solvent. These intermolecular hydrogen-bonds hinder the formation of tautomer, hence explaining the low quantum yield found in the protic solvent experiment. Especially for HBI complexing with methanol, only ESIntraPT occurs with small probability compared to HBI with water and ammonia.

Substitution by tert-butyl groups facilitates excited state proton transfer in hydroxylated triphenylimidazole frameworks more than it does for oxazole and thiazole analogs

“…In the work of Ramalho et al 19 , some functionals were tested and B3LYP was the most adequate functional employed in the study of an amino-naphthoquinone derivative capable of performing ESIPT. Also, previous studies demonstrated that the functional B3LYP is very reliable for obtaining the potential energy curves in the ground and excited states (see, for example, references 4,19,49,50,24,27,[43][44][45][46][47][48].…”

Heteroatom substitution effect on electronic structures, photophysical properties, and excited-state intramolecular proton transfer processes of 3-hydroxyflavone and its analogues: A TD-DFT study

“…From the method of choice, among seven tested functionals, the most suitable method for reproducing the enol absorption spectra of all molecules is the B3LYP because this method provides the most satisfactory agreement with the experimental data. Moreover, previous studies have been proven that the B3LYP and TD-B3LYP functionals with TZVP basis set are suitable to describe electronic and photophysical properties as well as the PT process of ESIPT molecules [29,[57][58][59][60][61][62]. Therefore, the B3LYP was further em ployed to optimize the enol form in the S 1 state and the keto form both in S 0 and the S 1 states of all molecules.…”

“…Solving Newton's equation of nuclear motion was achieved by the Velocity-Verlet algorithm [22]. The Born-Oppenheimer energies and gradients were obtained at each time step by mean of the TD-B3LYP method, which has been tested and used in dynamic simulations in previous studies [60][61][62][66][67][68]75]. All trajectories for each complex were simulated with a time step of 1 fs with the maximal duration of 500 fs, which is long enough to cover the pre-and post-PT regimes.…”

The alkoxylation effects on the excited‐state intramolecular proton transfer behaviors for 2,6‐bis(benzothiazolyl‐2‐yl)phenol fluorophore: A theoretical research

“…[16][17][18][19][20][21][22][23][24][25] As far as we know, one of the most challenging cases in photochemical field is the investigation of excited-state hydrogen bonding interactions in molecules due to both proton acceptor and donor moieties. [26][27][28][29][30] Accordingly, excited-state dynamical processes of hydrogen bonding molecules should be usually complicated by the fact that multiple equilibriums and various species can appear in excited states. In general, the individual or simultaneous ESIPT reaction suffered by these centers might give rise to the observation of different exciplexes of photo-tautomers, respectively.…”