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A Study of Competitive Multiple Hydrogen Bonding Effect and Its Associated Excited-State Proton Transfer Tautomerism

Abstract

1,8-Dihydroxynaphthalene-2,7-dicarbaldehyde (DHDA) has been strategically designed and synthesized in a aim to study the competitive multiple hydrogen bonding (H-bonding) effect and the associated excited-state intramolecular proton transfer reaction (ESIPT). In nonpolar solvents such as cyclohexane, equilibrium exists between two H-bonding isomers DHDA–23_OO and DHDA–23_OI (Scheme 1), which all possess double intramolecular H-bonds. In polar, aprotic solvents such as CH2Cl2, DHDA–23_OO becomes the predominant species. Due to various degrees of H-bond induced changes of electronic configuration each isomer reveals distinct absorption feature and excited-state behavior, in which DHDA–23_OI in cyclohexane undergoes double ESIPT in a stepwise manner, giving the first and second proton-transfer tautomer emissions maximized at ~500 nm and 660 nm, respectively. As for DHDA–23_OO both single and double ESIPT are prohibited, resulting in an intense normal 450 nm emission band. In a single crystal DHDA–23_OI is the dominant species, which undergoes excited state double proton transfer, giving intense 530 nm and 650 nm emission bands. The mechanism associated with competitive multiple H-bonding energetics and ESIPT was underpinned by detailed spectroscopy/dynamics and computational approaches.

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Publication details

The article was received on 24 Jul 2017, accepted on 03 Oct 2017 and first published on 03 Oct 2017


Article type: Paper
DOI: 10.1039/C7CP05002J
Citation: Phys. Chem. Chem. Phys., 2017, Accepted Manuscript
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    A Study of Competitive Multiple Hydrogen Bonding Effect and Its Associated Excited-State Proton Transfer Tautomerism

    Y. Chen, P. Wu, C. Peng, J. Shen, C. Tsai, W. Hu and P. Chou, Phys. Chem. Chem. Phys., 2017, Accepted Manuscript , DOI: 10.1039/C7CP05002J

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