Excited state intramolecular proton transfer mechanism of o-hydroxynaphthyl phenanthroimidazole

Abstract

By utilizing the density functional theory (DFT) and the time-dependent density functional theory (TDDFT), the excited state intramolecular proton transfer (ESIPT) mechanism of o-hydroxynaphthyl phenanthroimidazole (HNPI) is studied in detail. Upon photo is excited, the intramolecular hydrogen bond is obviously enhanced in the S 1 state, which thus promotes the ESIPT process. Hydrogen bond is shown to be strengthened via comparing the molecular structures and the infrared vibration spectra of the S 0 and S 1 states. Through analyzing the frontier molecular orbitals, we can conclude that the excitation is a type of the intramolecular charge transfer excitation, which also indicates the trend of proton transfer in S 1 state. The vertical excitation based on TDDFT calculation can effectively repeat the absorption and fluorescence spectra of the experiment. However, the fluorescence spectrum of normal structure, which is similar to the spectrum of isomer structure is not detected in the experiment. It can be concluded that the fluorescence measured in the experiment is attributed to both structures. In addition, by analyzing the potential energy curves (PECs) calculated by the B3LYP functional method, it can be derived that since the molecule to cross the potential barrier in the S 1 state is smaller than in the S 0 state and the reverse proton transfer process in the S 1 state is more difficult than in the S 0 state, the ESIPT occurs in the S 1 state.

The revelation of ESIPT behavior and fluoride response mechanism for (E)‐2‐(((1H‐benzo[d]imidazol‐2‐yl)‐imino)methyl)‐5‐(dimethylamino)‐phenol

“…Furthermore, the hydrogen bond strengthening or weakening could also be revealed based on monitoring the spectral shifts of vibrational modes involved in the formation of hydrogen bonds . The vibrational spectra of bip chromophore in the conjunct vibrational regions of the O‐H stretching mode have been shown in Figure .…”

“…The geometric optimizations of bip , bip‐open and bip‐pt were performed using DFT in the S 0 state and using TDDFT in the S 1 state. Especially, the TDDFT method has become a very useful tool to theoretically investigate the hydrogen bonding interaction that occurs in the excited states . In addition, Becke's three‐parameter hybrid exchange functional with Lee–Yang–Parr gradient‐corrected correlation (B3LYP functional) was selected in both the DFT and TDDFT methods .…”

“…Till now, many different sensing mechanisms, such as intramolecular charge transfer (ICT), photo‐induced electron transfer (PET), fluorescence resonance energy transfer (FRET), and excited state proton transfer (ESPT) and so forth, are relevant with intra‐ or inter‐ molecular hydrogen bond. Particularly, the excited state inter‐ and intra‐ molecular proton transfer (ESIPT) reactions have been drawing great attention due to their unique photo‐physical and photo‐chemical properties.…”

“…Even though this sensor has weak fluorescence, it was reported that the anion‐binding adduct of bip is expected to be highly fluorescent based on ESIPT channel experimentally, however, the mechanism of bip in excited state is very limitted. In effect, experimental spectroscopic techniques, such as steady‐state absorption spectroscopy, fluorescence spectroscopy and time resolved fluorescence spectroscopy, just provide the indirect information about photo‐physical and photo‐chemical properties . Up to now, the theoretical investigations about the bip are very scarce in addition to the experiments.…”

Theoretical Study on the Sensing Mechanism of Novel Hydrazine Sensor TAPHP and Its ESIPT and ICT Processes

“…Such a pioneering discovery soon led to a flurry of studies on the proton transfer mechanism. Recently, Han et al discovered that HB interaction can be enhanced in excited states Chai et al, 2009;Liu et al, 2018;Song et al, 2019). According to Weller, the ESIPT process of methyl salicylate was induced by its intramolecular HB.…”