The new competitive mechanism of hydrogen bonding interactions and transition process for the hydroxyphenyl imidazo [1, 2-a] pyridine in mixed liquid solution

Yongqing Li,Yunfan Yang,Yong Ding

doi:10.1038/s41598-017-01780-7

Yongqing Li, Yunfan Yang + Show 1 more

Open Access

https://doi.org/10.1038/s41598-017-01780-7

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Abstract

The new competitive mechanism of intermolecular and intramolecular hydrogen bond can be proposed with an improved mixed model. Upon the photoinduced process, the twisting intramolecular charge transfer (TICT) structure of the hydroxyphenyl imidazo [1, 2-a] pyridine (HPIP) can be obtained. TICT character prompts the fluorescent inactivation via non-radiative decay process. For exploring the photochemical and photophysical properties, the electronic spectra and the infrared (IR) vibrational spectra of titled compounds have been detailedly investigated. In addition, the frontier molecular orbitals (MOs) analysis visually reveals that the unbalanced electron population can give rise to the torsion of molecular structure. To further give an attractive insight into the non-radiative decay process, the potential energy curves have been depicted on the ground state (S0), the first excited state (S1) and the triple excited state (T1). Minimum energy crossing point (MECP) has been found in the S1 and T1 state. On the MECP, the intersystem crossing (ISC) might be dominant channel. The density functional theory (DFT) and the time-dependent density functional theory (TDDFT) methods have been throughout employed in the S0 state, T1 state and S1 state, respectively. The theoretical results are consistent with experiment in mixed and PCM model.

Highlights

Hydrogen bond is a non-covalent interaction between electronegative atom Y and covalent bond group X-H[1]
The HPIP in the THF solvent phase has a dual emitting in the polarizable continuum model (PCM) solvation, but the fluorescence of keto form isomer will be totally quenched via the twisting intramolecular charge transfer (TICT) character in the mixed liquid model
We are interested in the fluorescence quenching process, and we have speculated that the TICT structure might go through an intersystem crossing (ISC) process from S1 state to T1 state on the MECP41, 49–51

Summary

Results and Discussion

We primarily investigate the photophysics and photochemistry properties of HPIP. In this study a new competitive mechanism of intramolecular and intermolecular hydrogen bond will be investigated in the torsional process. Four stable structures have been found in the S0 state, the HPIP (a), the keto form of HPIP (k-HPIP) (b), the trans- keto form HPIP (trans-k-HPIP) (c) and the open-ended intramolecular hydrogen bond HPIP (o-HPIP) (d) have been shown in the Fig. 2. Four stable structures in the S1 state, the cis-HPIP (a), in PCM the k-HPIP (ik-HPIP) (b), the nearly vertical isomer form of HPIP (v-HPIP) (c) and the trans-k-HPIP (d) have been shown in the Fig. 3. The structure of cis-HPIP is near planar in the S1 state

Parameters of bonds Electronic state

Conclusions

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