Ramadass Radhan, Bereiter-Hahn Jürgen
Institute for Cell Biology and Neuroscience, Biocenter, JW Goethe University, Max-von-Laue-Strasse 9, D-60439 Frankfurt/Main, Germany.
J Phys Chem B. 2007 Jul 5;111(26):7681-90. doi: 10.1021/jp070378k. Epub 2007 Jun 9.
Photophysical properties of 2-(4-(dimethylamino)styryl)-1-methylpyridinium iodide (DASPMI) in various solvents were investigated using time- and space-correlated single photon counting. DASPMI is known to selectively stain mitochondria in living cells.1,2 The uptake and fluorescence intensity of DASPMI in mitochondria is a dynamic measure of membrane potential. Hence, an endeavor has been made to elucidate the mechanism of DASPMI fluorescence by obtaining spectrally resolved fluorescence decays in different solvents. A biexponential decay model was sufficient to globally describe the wavelength-dependent fluorescence in ethanol and chloroform. While in glycerol, a three-exponential decay model was necessary for global analysis. In the polar low-viscous solvent water, a monoexponential decay model fitted the decay data. The sensitivity of DASPMI to solvent viscosity was analyzed using various proportions of glycerol-ethanol mixtures. The lifetimes were found to increase with increasing solvent viscosity. The negative amplitudes of the short lifetime component found in chloroform and glycerol at the longer wavelengths validated the formation of new excited-state species from the initially excited state. Time-resolved emission spectra in chloroform and glycerol showed a biphasic increase of spectral width and emission maxima. The spectral width had an initial fast increase within 150 ps and a near constant thereafter. A three-state model of generalized scheme, on the basis of successive formation of locally excited state (LE), intramolecular charge transfer state (ICT), and twisted intramolecular charge transfer (TICT) state, has been proposed to explain the excited-state kinetics. The presumed role of solvation dynamics of ICT and TICT states leading to the asymmetrical broadening and structureless fluorescence has been substantiated by the decomposition of time-resolved emission spectra in chloroform, glycerol, and ethanol/glycerol mixtures.
利用时间和空间相关单光子计数技术研究了2-（4-（二甲基氨基）苯乙烯基）-1-甲基碘化吡啶鎓（DASPMI）在各种溶剂中的光物理性质。已知DASPMI能选择性地对活细胞中的线粒体进行染色。1,2 DASPMI在线粒体中的摄取和荧光强度是膜电位的动态指标。因此，人们致力于通过获取不同溶剂中光谱分辨的荧光衰减来阐明DASPMI荧光的机制。双指数衰减模型足以全局描述乙醇和氯仿中波长依赖的荧光。而在甘油中，全局分析需要三指数衰减模型。在极性低粘度溶剂水中，单指数衰减模型拟合了衰减数据。使用不同比例的甘油-乙醇混合物分析了DASPMI对溶剂粘度的敏感性。发现寿命随溶剂粘度的增加而增加。在较长波长下氯仿和甘油中发现的短寿命成分的负振幅证实了从初始激发态形成了新的激发态物种。氯仿和甘油中的时间分辨发射光谱显示光谱宽度和发射最大值呈双相增加。光谱宽度在150 ps内有一个初始的快速增加，此后几乎保持恒定。基于局部激发态（LE）、分子内电荷转移态（ICT）和扭曲分子内电荷转移（TICT）态的连续形成，提出了一个广义方案的三态模型来解释激发态动力学。氯仿、甘油和乙醇/甘油混合物中时间分辨发射光谱的分解证实了ICT和TICT态的溶剂化动力学导致不对称展宽和无结构荧光的假定作用。
