Department of Chemistry, Indian Institute of Technology, Kharagpur 721302, WB, India.
J Phys Chem B. 2012 Aug 9;116(31):9482-91. doi: 10.1021/jp305095n. Epub 2012 Jul 31.
The dynamics of photoisomerization of 3,3'-diethyloxadicarbocyanine iodide (DODCI) has been investigated inside micellar environment formed by a surfactant-like ionic liquid, 1-butyl-3-methylimidazolium octyl sulfate ([C(4)mim][C(8)SO(4)]) and also in binary mixture of another ionic liquid, N,N,N-trimethyl-N-propyl ammonium bis(trifluoromethanesulfonyl) imide, ([N(3111)][Tf(2)N]) with methanol, acetonitrile, and n-propanol by using steady-state and picosecond time-resolved fluorescence spectroscopy. The entrapment of DODCI into the [C(4)mim][C(8)SO(4)] micellar environment led to the enhanced fluorescence intensity along with ~13 nm red shift in the emission maxima. A sharp increase in the fluorescence quantum yield (Φ) and the lifetime (τ(f)) near the critical micelle concentration (cmc) range is observed followed by saturation at higher concentration. As a result of partitioning of the probe molecules in the micellar phase from water, the nonradiative rate constant (k(nr)) of DODCI decreases 2.7 times than in water. The retardation of isomerization rate is due to high microviscosity of the micellar system compared to bulk water. In order to understand how the rate of isomerization depends on polarity as well as viscosity, we have measured isomerization rate in neat [N(3111)][Tf(2)N] and its mixtures with polar solvents, like methanol, acetonitrile, and n-propanol. The addition of methanol and n-propanol increases the polarity, but viscosity of the medium decreases. The nonradiative rate constant that represents the rate of photoisomerization decreases with the addition of the polar solvent in [N(3111)][Tf(2)N]. Complete analysis of all the experimental results indicate that viscosity is the sole parameter that regulates the rate of photoisomerization. Temperature-dependent k(nr) are used to determine the activation energy (E(a)) in 100 mM [C(4)mim][C(8)SO(4)] solution and neat [N(3111)][Tf(2)N] system.
3,3'-二乙基氧杂羰花青碘化物（DODCI）的光异构化动力学已在表面活性剂类似的离子液体 1-丁基-3-甲基咪唑𬭩辛基硫酸盐（[C（4）mim][C（8）SO（4）]）形成的胶束环境中以及在另一种离子液体 N，N，N-三甲基-N-丙基铵双（三氟甲磺酰基）亚胺，[N（3111）][Tf（2）N]）与甲醇、乙腈和正丙醇的二元混合物中进行了研究，采用稳态和皮秒时间分辨荧光光谱法。DODCI 被捕获到 [C（4）mim][C（8）SO（4）]胶束环境中导致荧光强度增强，发射峰最大红移约 13nm。在临界胶束浓度（cmc）范围内观察到荧光量子产率（Φ）和寿命（τ（f））的急剧增加，随后在较高浓度下达到饱和。由于探针分子从水中分配到胶束相中，DODCI 的非辐射速率常数（k（nr））比在水中降低了 2.7 倍。由于与体相比，胶束系统的微观粘度较高，异构化速率减慢。为了了解异构化速率如何依赖于极性和粘度，我们在纯[N（3111）][Tf（2）N]及其与甲醇、乙腈和正丙醇等极性溶剂的混合物中测量了异构化速率。甲醇和正丙醇的加入增加了极性，但介质的粘度降低。表示光异构化速率的非辐射速率常数随着[N（3111）][Tf（2）N]中极性溶剂的加入而降低。对所有实验结果的综合分析表明，粘度是调节光异构化速率的唯一参数。温度依赖性 k（nr）用于确定 100mM [C（4）mim][C（8）SO（4）]溶液和纯[N（3111）][Tf（2）N]系统中的活化能（E（a））。
