Journal
MOLECULAR PHYSICS
Volume 120, Issue 5, Pages -Publisher
TAYLOR & FRANCIS LTD
DOI: 10.1080/00268976.2021.2007307
Keywords
Excited-state proton transfer; intramolecular hydrogen bond; potential energy surfaces; solvent polarity
Funding
- China Postdoctoral Science Foundation [2020M682154]
- National Natural Science Foundation of China [21873114]
- LiaoNing Revitalization Talents Program [XLYC1807162]
- Shenyang High-level Innovative Talents Program [RC200565]
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The study investigated the proton transfer mechanism in a system containing double hydrogen bonds under different solvent polarities, finding that enhanced hydrogen bonding in the first excited state facilitates proton transfer. Employing frontier molecular orbital theory, it was demonstrated that the system undergoes charge density redistribution upon photoexcitation.
Excited-state intramolecular proton transfer (ESIPT) has been well investigated in recent years, whereas we investigated the system containing double hydrogen bonds. We explore the influence of solvent polarity on the proton transfer mechanism for 9,9-dimethyl-3,6-dihydroxy-2,7-bis(4,5-dihydro-4,4-dimethyl-2-oxazolyl)fluorene compound ((Oxa-OH)(2)). We consider three solvents with different polarities: cyclohexane, chloroform and acetonitrile. Various analytical methods indicate that hydrogen bonding is enhanced in the first excited state, which facilitates the proton transfer within the excited-state molecule. The frontier molecular orbital theory is employed to demonstrate that the system is subjected to photoexcitation to generate charge density redistribution. Three-dimensional potential energy surfaces are also constructed along the direction of hydrogen bond elongated, and their corresponding projection in the X-axis and Y-axis planes are plotted. The comparison of the potential barriers and the transition state structures of each proton transfer path reveals the excited-state intramolecular single proton transfer mechanism of the system. By comparing the potential barriers in different solvents, we also propose a mechanism that can modulate the excited-state proton transfer by changing the solvent polarity.
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