Ghosh Deborin, Ahamed Giasuddin, Batuta Shaikh, Begum Naznin Ara, Mandal Debabrata
Department of Chemistry, University College of Science and Technology, University of Calcutta , 92, A.P.C. Road, Kolkata 700 009, India.
Bio-Organic Chemistry Lab, Department of Chemistry, Visva-Bharati University , Santiniketan 731 235, India.
J Phys Chem A. 2016 Jan 14;120(1):44-54. doi: 10.1021/acs.jpca.5b09681. Epub 2016 Jan 5.
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.
在3-羟基黄酮的3'，4'-位引入亚甲二氧基取代基对其质子转移响应产生了显著影响，这与著名的4'-N，N-二烷基氨基类似。该取代基潜在的供电子性质有助于在分子的激发烯醇形式中维持高度的电荷分离，这种形式在相对极性的溶剂中得以稳定，于是烯醇→互变异构体激发态分子内质子转移（ESIPT）速率降低。氢键溶剂通过干扰促进ESIPT的分子内氢键而进一步延缓了该过程。在这些溶剂中，氢键供体似乎比氢键受体更有效地抑制ESIPT。飞秒荧光实验表明，即使在后者中，随着溶剂氢键碱性的增加，ESIPT时间常数也会稳步延长。
