New Excited-State Proton Transfer Mechanisms for 1,8-Dihydroxydibenzo[a,h]phenazine

Abstract

The excited state intramolecular proton transfer (ESIPT) mechanisms of 1,8-dihydroxydibenzo[a,h]phenazine (DHBP) in toluene solvent have been investigated based on time-dependent density functional theory (TD-DFT). The results suggest that both a single and double proton transfer mechanisms are relevant, in constrast to the prediction of a single one proposed previously (Piechowska et al. J. Phys. Chem. A 2014, 118, 144-151). The calculated results show that the intramolecular hydrogen bonds were formed in the S0 state, and upon excitation, the intramolecular hydrogen bonds between -OH group and pyridine-type nitrogen atom would be strengthened in the S1 state, which can facilitate the proton transfer process effectively. The calculated vertical excitation energies in the S0 and S1 states reproduce the experimental UV-vis absorption and fluorescence spectra well. The constructed potential energy surfaces of the S0 and S1 states have been used to explain the proton transfer process. Four minima have been found on the S1 state surface, with potential barriers between these excited-state minima of less than 10 kcal/mol, which supports concomitant single and double proton transfer mechanisms. In addition, the fluorescence quenching can be explained reasonably based on the proton transfer process.

A theoretical study about the excited state intermolecular proton transfer mechanisms for 2-phenylimidazo[4,5-b]pyridine in methanol solvent

“…As is well-known, the basic photochemical and photophysical principle of ESIPT is that ESIPT molecules possessing proton donors (O-H or N-H) and acceptors (carbonyl oxygen or aromatic nitrogen) may undergo the ESIPT process upon electronic excitation. [6][7][8] Generally, ESIPT reactions could result in a corresponding balance between enol and keto tautomers, stimulating a dual emission and large Stokes shis. [9][10][11][12] Moreover, two uorescence bands are observed and a broader range of the steady-state emission can be covered, making these ESPT molecules suitable for optical chemosensors, white-emitting OLEDs, material chemistry, and UV lters, among other applications.…”

TDDFT assessment of excited state intramolecular proton transfer in a panel of chromophore 2-hydroxypyrene-1-carbaldehyde

“…Ever since the seminal experimental observation of the excited-state intramolecular proton transfer (ESIPT) reaction of methyl salicylate (MS) by Weller et al in the middle of the last century [1], the phenomenon of photoinduced proton transfer process has attracted countless works in many fields of chemistry and molecular biology [2][3][4][5][6][7][8][9][10][11][12][13][14][15]. A very fascinating feature of molecules undergoing ESIPT is the presence of a strong intramolecular hydrogen bond, in which the acidity and basicity relations can be controllable by photoexcitation.…”

Role of intramolecular hydrogen bonding in the excited-state intramolecular double proton transfer (ESIDPT) of calix[4]arene: A TDDFT study

“…Proton transfer reactions in the excited state attract a lot of attention in physical, chemical, and biological systems [7][8][9][10][11][12][13]. Due to molecular structure, proton transfer can be intermolecular as well as intramolecular.…”