Excited-state intramolecular proton transfer and conformational relaxation in 4'-N,N-dimethylamino-3-hydroxyflavone doped in acetonitrile crystals

The effect of intermolecular interactions on excited-state intramolecular proton transfer (ESIPT) in 4'-N,N-dimethylamino-3-hydroxyflavone (DMHF) doped in acetonitrile crystals was investigated by measuring its temperature dependence of steady-state fluorescence excitation and fluorescence spec...

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Bibliographic Details
Published in:Physical chemistry chemical physics : PCCP 2016, Vol.18 (41), p.28564-28575
Main Authors: Furukawa, Kazuki, Yamamoto, Norifumi, Hino, Kazuyuki, Sekiya, Hiroshi
Format: Article
Language:English
Subjects:
Acetonitrile
Crystals
Excitation
Excitation spectra
Fluorescence
Spectra
Spectral emissivity
Tautomers
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Summary:The effect of intermolecular interactions on excited-state intramolecular proton transfer (ESIPT) in 4'-N,N-dimethylamino-3-hydroxyflavone (DMHF) doped in acetonitrile crystals was investigated by measuring its temperature dependence of steady-state fluorescence excitation and fluorescence spectra and picosecond time-resolved spectra. The relative intensity of emission from the excited state of the normal form (N*) to that from the excited state of the tautomer form (T*) and spectral features changed markedly with temperature. Unusual changes in the spectral shift and spectral features were observed in the fluorescence spectra measured between 200 and 218 K, indicating that a solid-solid phase transition of DMHF-doped acetonitrile crystals occurred. Time-resolved fluorescence spectra suggested conformational relaxation of the N* state competed with ESIPT after photoexcitation and the ESIPT rate increased with temperature in the low-temperature phase of acetonitrile. However, the intermolecular interaction of N* with acetonitrile in the high-temperature phase markedly stabilized the potential minimum of the fluorescent N* state and slowed the ESIPT. This stabilization can be explained by reorganization of acetonitrile originating from the strong electric dipole-dipole interaction between DMHF and acetonitrile molecules.
ISSN:1463-9076
1463-9084
DOI:10.1039/c6cp04322d