Department of Chemistry, University of Washington, Seattle, Washington 98195, USA.
J Phys Chem A. 2010 Jul 15;114(27):7331-7. doi: 10.1021/jp102194u.
The connection between photoluminescence (PL) intermittency and excited-state kinetics is explored for 2',7'-dichlorofluorescein (DCF) isolated in crystals of potassium acid phthalate (KAP) using time-tagged, time-resolved, time-correlated single-photon counting (T3R-TCSPC). In this technique, PL intermittency or "blinking" is measured in conjunction with the time of photon arrival relative to photoexcitation, allowing for the correlation of emissive intensities and excited-state decay kinetics of single molecules. The blinking trace is parsed into emissive and nonemissive segments using change-point-detection analysis, and the duration of these segments are used to quantify PL intermittency. The results presented here demonstrate that two populations of DCF exist in KAP, with one population demonstrating single-exponential excited state decay over the course of the blinking trace, and the other demonstrating stretched-exponential decay. Molecules demonstrating single-exponential decay also demonstrate modest intensity variation in the blinking trace. Correlation of the emission intensity and excited-state lifetimes demonstrates that for these molecules spectral diffusion is largely responsible for the evolution in emission intensity. In contrast, molecules demonstrating nonexponential excited-state decay vary in emission intensity. Correlation of the emissive intensities with the excited-state lifetimes demonstrates that these molecules undergo changes in both radiative and nonradiative decay rate constants as well as spectral diffusion. These observations suggest that DCF exists in two environments in KAP differentiated by the propensity for proton-transfer with the surrounding KAP matrix. The results presented here provide further insight into the origin of PL intermittency demonstrated by DCF in KAP and related systems.
用时间标记、时间分辨、时间相关的单光子计数（T3R-TCSPC）研究了 2'，7'-二氯荧光素（DCF）在邻苯二甲酸氢钾（KAP）晶体中的光致发光（PL）间歇性与激发态动力学之间的关系。在这项技术中，PL 间歇性或“闪烁”与光子到达相对于光激发的时间一起测量，允许单个分子的发射强度和激发态衰减动力学相关联。使用变化点检测分析将闪烁迹线解析为发射和非发射段，并使用这些段的持续时间来量化 PL 间歇性。这里呈现的结果表明，在 KAP 中存在两种 DCF 群体，一种群体在闪烁迹线的过程中表现出单指数激发态衰减，另一种群体表现出伸展指数衰减。表现出单指数衰减的分子在闪烁迹线中也表现出适度的强度变化。发射强度与激发态寿命的相关性表明，对于这些分子，光谱扩散是发射强度演变的主要原因。相比之下，表现出非指数激发态衰减的分子在发射强度上变化。发射强度与激发态寿命的相关性表明，这些分子经历了辐射和非辐射衰减速率常数以及光谱扩散的变化。这些观察结果表明，DCF 在 KAP 中存在两种环境，其与周围 KAP 基质的质子转移倾向不同。这里呈现的结果提供了对 DCF 在 KAP 和相关系统中表现出的 PL 间歇性的起源的进一步了解。
