Solvent effect on the excited-state intramolecular double proton transfer of 1,3-bis(2-pyridylimino)-4,7-dihydroxyisoindole

Abstract

Density functional theory (DFT) and time-dependent density functional theory (TDDFT) are used to study the solvatochromic effect and the excited-state intramolecular double proton transfer (ESIDPT) of 1,3-Bis(2-pyridylimino)-4,7-dihydroxyisoindole (BPI-OH) in different kinds of solvents. The hydrogen bonding parameters and IR spectra reveal that in the excited state, the strength of excited hydrogen bond increase with the decrease of solvent polarity. Furthermore, the reduction density gradient (RDG) analysis confirms the corresponding conclusion. Frontier molecular orbitals (FMOs) are analyzed, illuminating that the smaller the polarity of solvent, the smaller the energy gap between the HOMO and LUMO. The structures of BPI-OH (N) (normal), BPI-OH (T 1 ) (single), and BPI-OH (T 2 ) (double) were optimized. Previous reports found the double protons in BPI-OH molecule are transferred step-by-step process BPI-OH(N)→BPI-OH(T 1 )→BPI-OH(T 2 ) in the ground state (S 0 ) and the first excited singlet state (S 1 ). Here, the potential energy curves of O 1 -H 2 and O 4 -H 5 in the S 0 and S 1 states were scanned in four kinds of solvents, respectively. It was found that in S 1 state, BPI-OH(N)→BPI-OH(T 1 ) was more prone to proton transfer than BPI-OH(T 1 )→BPI-OH(T 2 ). In addition, by comparing the reaction energy barriers of the four kinds of solvents, it can be found that ESIPT is difficult to occur with the increase of solvent polarity. Meanwhile, it was also studied that MeOH as an explicit solvent was more likely to promote the ESIPT process than other implicit solvents.

Insights into photo‐induced excited state intramolecular proton transfer behavior for the novel 2‐([1, 1′‐biphenyl]‐4‐yl)‐3‐hydroxy‐4H‐chromen‐4‐one system: Effects of solvent polarity

“…Visibly, the accumulation of electron densities around the O 3 acceptor promotes the ESIPT reaction for B‐bph‐fla‐OH system. Empirically, the energy difference between HOMO and LUMO could reflect the target molecular activity in excited state via excitation to a large extent 46–49 . Therefore, we also calculate the energy difference in five solvents.…”

“…Empirically, the energy difference between HOMO and LUMO could reflect the target molecular activity in excited state via excitation to a large extent. [46][47][48][49] Therefore, we also calculate the energy difference in five solvents. The gap is 3.704, 3.710, 3.723, 3.729, and 3.732 eV in CYC, BEN, CHL, ACE, and DMSO, respectively.…”

Photochemical Mechanisms of Hydroxyquinoline Benzimidazole: Insights from Electronic Structure Calculations and Nonadiabatic Dynamics Simulations

“…The explorations found that there are two types of ESIDPT, e.g., cascade and noncascade. The cascade form has been shown to undergo a stepwise transfer of two protons, whereas for the noncascade form, the mechanism is still not clear. − Recently, Kumar et al synthesized an ESIDPT material hydroxyquinoline benzimidazole (HQB) with two different types of hydrogen bonds (see Scheme ). The potential energy curves calculated by using density functional theory (DFT) and time-dependent DFT (TD-DFT) methods indicate that the HQB system could undergo two proton transfers in different sequences during the deactivation pathway from the S 1 excited state back to the ground state.…”

Photophysical Properties of (E)-1-(4-(Diethyla-mino)-2-hydroxybenzylidene)-4,4-dimethylthiosemicarbazide Compound and Its Triple Fluorescence Emission Mechanism: A Theoretical Perspective

“…The excited-state intramolecular proton-transfer (ESIPT) process was a photophysical process that induced the isomerization of intramolecular hydrogen bonds (IHBs) from enol to keto in organic molecules after photoexcitation. − The presence of ESIPT resulted in a reduction of the first singlet energy level − and a redshift of the emission wavelength; − thus, the ESIPT molecule usually had a large Stokes shift. − Molecules with ESIPT properties were considered to have potential applications in fluorescence probes, − organic luminescent materials, − and biomedicine. − In 1950, Weller first reported the ESIPT process in methyl salicylate . Subsequently, numerous scholars were committed to exploring the molecular mechanism of the ESIPT reaction and its application value both experimentally and theoretically …”