Oncul Sule, Demchenko Alexander P
TUBITAK Research Institute for Genetic Engineering and Biotechnology, RIGEB, 41470 Gebze-Kocaeli, Turkey.
Spectrochim Acta A Mol Biomol Spectrosc. 2006 Sep;65(1):179-83. doi: 10.1016/j.saa.2005.10.002. Epub 2006 Feb 2.
The 3-hydroxyflavone (3HF) and its derivatives are the classical objects in the studies of the mechanisms of excited-state intramolecular proton transfer (ESIPT) reaction due to very frequent observation of two separate bands in fluorescence emission belonging to reactant and reaction product. Those of them possessing electron-donor groups in 4' position find many applications as fluorescence sensors and probes because of their much higher sensitivity of their two-band ratiometric response to interactions with the environment. We report on the strong differences between 3HF and such derivatives in the behavior of their fluorescence spectra as a function of temperature. The thermal quenching changes the intensity ratio of two bands strongly for 3HF but does not change it for its studied derivatives. These results are interpreted in terms of different kinetic mechanisms of ESIPT reaction. In 3HF the equilibrium between the two excited-state species is not established prior to emission, so that the ESIPT reaction is under kinetic control, but in these derivatives the equilibrium is established faster than the emission and the reaction is under thermodynamic control. We suggest that the thermal perturbation of fluorescence spectra can be an extremely simple and convenient alternative to time-resolved spectroscopy for determining if slow irreversible or fast reversible ESIPT reaction gives rise to two bands of fluorescence spectra of similar magnitude. This is essential for the development of new wavelength-ratiometric fluorescence sensors and probes.
3-羟基黄酮（3HF）及其衍生物是激发态分子内质子转移（ESIPT）反应机制研究中的经典对象，因为在荧光发射中经常观察到属于反应物和反应产物的两个独立谱带。其中那些在4'位具有供电子基团的化合物，由于其对与环境相互作用的双波段比率响应具有更高的灵敏度，因而作为荧光传感器和探针有许多应用。我们报道了3HF及其衍生物在荧光光谱行为随温度变化方面的显著差异。热猝灭对3HF的两个谱带强度比有强烈影响，但对其研究的衍生物则没有影响。这些结果根据ESIPT反应的不同动力学机制进行了解释。在3HF中，两个激发态物种之间的平衡在发射之前未建立，因此ESIPT反应处于动力学控制之下，但在这些衍生物中，平衡建立得比发射快，反应处于热力学控制之下。我们认为，荧光光谱的热扰动可以是一种极其简单方便的替代时间分辨光谱的方法，用于确定缓慢不可逆或快速可逆的ESIPT反应是否产生幅度相似的两个荧光光谱带。这对于开发新的波长比率荧光传感器和探针至关重要。
