利用纳秒激光闪光光解技术研究噻吨酮光化学动力学的pH值效应

最近一种对pH值敏感的噻吨酮衍生物荧光探针被报道. 因此，揭示其pH值效应的根本原因能够为将来设计新型荧光探针提供重要的参考. 本文利用纳秒激光闪光光解技术研究了噻吨酮分子本身光化学性质对pH值的依赖性，观测了噻吨酮以及噻吨酮与二苯胺构成的二元体系的瞬态吸收光谱和相应动力学变化. 除了已知的³TX^3*特征吸收峰外，对光谱中其它主要吸收峰(417、518、673和780 nm)进行了归属，证实了光照条件下噻吨酮与二苯胺之间的多步反应机制. 其中，在强酸(pH=3.0)条件下，噻吨酮和质子化的噻吨酮(TXH⁺)存在动态平衡，并且高的质子浓度促进了³TX^3*的主要衰减通道由电子转移变为质子亲和过程，所得到的初级产物³TXH^+*和TX^·-将经历不同的次级过程反应. 在较宽的pH范围内(从5.0到13.0)，总反应机理和反应速率都没有显著的变化.

pH Dependence of Photochemical Kinetics of Thioxanthen-9-one from Nanosecond Time-resolved Laser Flash Photolysis

pH dependent fluorescence emission of a thioxanthone-based probe has been re-ported recently. The potential deter-minant factors of pH dependence may provide important clues to design novel thioxanthone-based probes in the fu-ture. pH dependence of photochemical kinetics of thioxanthone itself was inves-tigated in this work using nanosecond time-resolved laser flash photolysis. The nanosecond time-resolved transient absorption spectra and kinetics of TX in aqueous acetonitrile were recorded, as well as for a model reaction system including TX with diphenylamine (DPA) as a co-initiator. Besides the well-known absorption peak of ³TX^3*, other peaks at 417, 518, 673 and 780 nm, have been reliably attributed to major intermediates in the overall reaction between TX and DPA with photolysis, which has been con rmed to occur along a multistep process. In the strong acidic solution (pH 3.0), TX and protonated TX ions (TXH⁺) coexist due to protonated equilibrium. Consequently, high proton concentration promotes the predominant decay pathway after photolysis from electron transfer to proton a nity. Subsequently, the different primary products, ³TXH⁺ or TX^·-, proceed different secondary reaction channels. In addition, within the wide pH range from weak acid (pH=5.0) to alkaline solution (pH=13.0), the overall reaction mechanism and rates do not show visible changes.