Optical anti-counterfeiting is one of the important fields of optical physics.The research and development of optical anti-counterfeiting materials based on single molecule system can reduce the production cost and simplify the production process.In order to develop new anti-counterfeiting materials and anti-counterfeiting technology, it is an effective strategy to combine the solvation effect and photochromism.Due to its sensitivity to the environment, the excited state proton transfer process can be artificially controlled in the intramolecular (ESIPT) or intermolecular (ESPT) by solvation effect, which will lead to the different luminescence properties of the molecular system.

The photophysical and photochemical kinetics of 1-hydroxypyrene-2-carbaldehyde (HP) in acetonitrile (ACN) and dimethyl sulfoxide (DMSO) solvents was investigated by using femtosecond transient absorption spectroscopy and time-dependent density functional theory.In ACN, it is proved that HP molecule undergoes ESIPT process in S1 state and the fluorescence quenching mechanism of HP molecule is found.In contrast, HP molecule has obvious fluorescence phenomenon in DMSO solvent.The interaction between solute and solvent destroys the intramolecular hydrogen bond of HP molecule and inhibits the possibility of ESIPT process of HP molecule.Before the radiation fluorescence, HP molecules experienced the deprotonization process (ESPT) on the 196 fs time scale and the carbon carbon single bond rotation process on the time scale of 27 ps.The reason of carbon carbon single bond rotation is the repulsion between carbonyl oxygen and hydroxyl oxygen, which is caused by the charge redistribution after the molecule is excited.In conclusion, the completely different fluorescence of HP molecules in the above solvents depends on the existence of intramolecular hydrogen bonds, which leads to completely different photochemical mechanisms.Based on the above mechanism, PMMA films were prepared by HP and ACN, and the anti-counterfeiting writing was successfully carried out with DMSO solvent.

The research results have realized a new way of single molecule optical anti-counterfeiting based on the excited state proton transfer process, which is considered to provide a lot of novel conclusions. The photophysical and photochemical mechanisms are revealed by combining experimental and theoretical methods.The results were published in dyes and segments under the title of "optical anti-counterfeiting of a single molecule by two solvents based on intra - and interactive excited state proton transfer mechanisms".The co authors of the paper are professor quartz, Professor Zhang Xiaoan and Professor Ding Dajun, and the co first author is lecturer Yin hang and Associate Professor Zhang Yumo.

Link to the full text of the paper:https://www.sciencedirect.com/science/article/pii/S014372081831283X?via%3Dihub