title: Effect of an Electron-Donating Substituent at the 3',4'-position of 3-Hydroxyflavone: Photophysics in Bulk Solvents.
abstract: Introduction of the methylenedioxy substituent group in the 3',4'-position of 3-hydroxyflavone produced a significant impact on its proton-transfer response, much like the well-known 4'-N,N-dialkylamino group. The potential electron-donating property of the substituent helped sustain a high degree of charge separation in the excited enolic form of the molecule, which was stabilized in relatively polar solvents, whereupon the enol → tautomer excited state intramolecular proton-transfer (ESIPT) rate decreased. Hydrogen-bonding solvents caused further retardation by interfering with the intramolecular hydrogen bond that promotes ESIPT. Among these solvents, hydrogen bond donors appear to be more efficient ESIPT inhibitors than hydrogen bond acceptors. Femtosecond fluorescence experiments revealed that even among the latter the ESIPT time-constants become steadily longer as the hydrogen bond basicity of the solvent increases.
authors.affiliation: Department of Chemistry, University College of Science and Technology, University of Calcutta , 92, A.P.C. Road, Kolkata 700 009, India.
authors.forename: Deborin
authors.initials: D
authors.lastname: Ghosh
authors.affiliation: Department of Chemistry, University College of Science and Technology, University of Calcutta , 92, A.P.C. Road, Kolkata 700 009, India.
authors.forename: Giasuddin
authors.initials: G
authors.lastname: Ahamed
authors.affiliation: Bio-Organic Chemistry Lab, Department of Chemistry, Visva-Bharati University , Santiniketan 731 235, India.
authors.forename: Shaikh
authors.initials: S
authors.lastname: Batuta
authors.affiliation: Bio-Organic Chemistry Lab, Department of Chemistry, Visva-Bharati University , Santiniketan 731 235, India.
authors.forename: Naznin Ara
authors.initials: NA
authors.lastname: Begum
authors.affiliation: Department of Chemistry, University College of Science and Technology, University of Calcutta , 92, A.P.C. Road, Kolkata 700 009, India.
authors.forename: Debabrata
authors.initials: D
authors.lastname: Mandal