Ghosh Deborin, Batuta Shaikh, Das Sreeparna, Begum Naznin Ara, Mandal Debabrata
‡Bio-Organic Chemistry Lab, Department of Chemistry, Visva-Bharati University, Santiniketan 731 235, India.
J Phys Chem B. 2015 Apr 30;119(17):5650-61. doi: 10.1021/acs.jpcb.5b00021. Epub 2015 Apr 20.
Photophysical studies on the 4'-N,N-dimethylamino-3-hydroxyflavone fluorophore were performed in hydrogen-bonding solvents. Both in hydrogen-bonding acids and bases, clear evidence of excited state intramolecular proton transfer (ESIPT) emerged from steady-state and time-resolved spectroscopies. The same was also observed for the fluorophores residing in the hydrophilic shell region of aqueous micelles, where they come into close contact with water molecules at the micelle-water interface. Slow ∼100 ps ESIPT time-constants were determined in these systems that correlated well with solvation dynamics. The slow ESIPT time-constants are attributed to activated barrier crossing from the solvent-relaxed enol form to tautomer form in the excited state energy surface of the flavone. In contrast to the barrier-less ESIPT occurring in early (<1 ps) time-scales, this activated proton-transfer event necessarily requires extensive reorganization of flavone···solvent intermolecular hydrogen bonds, a process heavily modulated by the relatively slower dynamics of solvent relaxation around the excited fluorophore.
在氢键溶剂中对4'-N,N-二甲基氨基-3-羟基黄酮荧光团进行了光物理研究。在氢键酸和碱中，稳态和时间分辨光谱均清楚地证明了激发态分子内质子转移（ESIPT）的存在。对于存在于水性胶束亲水壳层区域的荧光团也观察到了同样的现象，在该区域它们在胶束-水界面与水分子紧密接触。在这些系统中测定了约100 ps的缓慢ESIPT时间常数，其与溶剂化动力学有很好的相关性。缓慢的ESIPT时间常数归因于在黄酮激发态能量表面上从溶剂弛豫的烯醇形式到互变异构体形式的活化势垒穿越。与早期（<1 ps）时间尺度上发生的无势垒ESIPT相反，这种活化质子转移事件必然需要黄酮···溶剂分子间氢键的广泛重组，这一过程受到激发荧光团周围相对较慢的溶剂弛豫动力学的严重调节。
