A novel non-fluorescent excited state intramolecular proton transfer phenomenon induced by intramolecular hydrogen bonds: an experimental and theoretical investigation.

Hang Yin,Hui Li,Ying Shi,Hongming Wang,Chengyan Ruan,Guomin Xia,Dajun Ding,Mingxing Jin

doi:10.1038/srep19774

Abstract

Two molecules, 1-hydroxypyrene-2-carbaldehyde (HP) and 1-methoxypyrene-2-carbaldehyde (MP) were explored. We investigated their photophysical properties, using experimental transient absorption and theoretical density functional theory/time-dependent density functional theory (DFT/TDDFT). HP and MP have similar geometric conformations but exhibit entirely different photophysical properties upon excitation into the S1 state. In contrast to traditional excited state intramolecular proton transfer (ESIPT) in molecules that exhibit either single or dual fluorescence, HP has an unusual non-fluorescent property. Specifically, the ultrafast ESIPT process occurs in 158 fs and is followed by an intersystem crossing (ISC) component of 11.38 ps. In contrast to HP, MP undergoes only an 8 ps timescale process, which was attributed to interactions between solute and solvent. We concluded that this difference arises from intramolecular hydrogen bonds (IMHBs), which induce drastic structural alterntion upon excitation.

Highlights

Figure 2. 3D image plots of the transient absorption for HP (a) and MP (b) in CHX after excitation at 400 nm
We found that the hydrogen bonded quasi-aromatic chelating ring in the excited state becomes smaller, which facilitates the excited state intramolecular proton transfer (ESIPT) process
Femtosecond transient absorption spectroscopy and DFT/TDDFT were performed to investigate the photoexcitation of HP and MP

Summary

Introduction

Figure 2. 3D image plots of the transient absorption for HP (a) and MP (b) in CHX after excitation at 400 nm. In our previous report[26], we theoretically investigated the salicylaldehyde (SA) molecule, which has exclusively intramolecular O–H⋅ ⋅ ⋅ O hydrogen bonds that form a strong quasi-aromatic chelating ring. We found that the hydrogen bonded quasi-aromatic chelating ring in the excited state becomes smaller, which facilitates the ESIPT process. We believe that the ESIPT system under the effect of IMHBs can exhibit non-fluorescence in addition to single and dual fluorescence. The six-membered, intramolecularly hydrogen-bonded system HP is an ideal model to explore the effect of IMHBs on the ESIPT system. To shed light on the ESIPT dynamics of HP, we report a combined experimental and theoretical method to investigate the HP and MP molecules and to confirm experimental results and discover more detailed information

Methods

Results

Conclusion