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首页> 外文期刊>RSC Advances >Different mechanisms of ultrafast excited state deactivation of coumarin 500 in dioxane and methanol solvents: experimental and theoretical study
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Different mechanisms of ultrafast excited state deactivation of coumarin 500 in dioxane and methanol solvents: experimental and theoretical study

机译：二恶烷和甲醇溶剂中香豆素500超快激发态失活的不同机理：实验和理论研究

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摘要

Solute-solvent intermolecular photoinduced intramolecular charge transfer (ICT) and twisted intramolecular charge transfer (TICT) states are proposed to account for the unusual properties of coumarin 500 (C500) in 1,4-dioxane (Diox) and methanol (MeOH) solvents. Our femtosecond transient absorption experiment on C500 shows that in Diox, there exists a single exponential component with a time constant of tau(1) similar to 1.4 ps, however in MeOH two exponential components with lifetimes of tau(1) similar to 0.5 ps and tau(2) similar to 8.0 ps are observed. DFT and TDDFT methods were used to optimize the geometries of complexes C500-Diox and C500-(MeOH)(3) in the ground and excited states, respectively. They show that the rapid decay time could be due to ICT and ICT -> TICT could be responsible for the slow decay time. Strengthening of the hydrogen bond N-H center dot center dot center dot O-H and the weakening of the hydrogen bond N center dot center dot center dot H-O in the excited state of the C500-(MeOH)(3) complex could facilitate the process of ICT from the 7-NHEt group to the CF3 group and induce the formation of the TICT state in hydrogen bonding with MeOH. Together, the experimental and theoretical results reveal that C500 exhibits unusual deactivation mechanisms in Diox and MeOH solvents.
机译：提出了溶剂溶剂分子间光诱导的分子内电荷转移（ICT）和扭曲的分子内电荷转移（TICT）状态，以说明香豆素500（C500）在1,4-二恶烷（Diox）和甲醇（MeOH）溶剂中的异常性质。我们在C500上进行的飞秒瞬态吸收实验表明，在Diox中，存在一个时间常数为tau（1）类似于1.4 ps的指数成分，但是在MeOH中存在两个寿命为tau（1）类似于0.5 ps的指数成分，并且观察到类似于8.0 ps的tau（2）。 DFT和TDDFT方法分别用于优化配合物C500-Diox和C500-（MeOH）（3）在基态和激发态下的几何构型。他们表明，快速衰减时间可能是由于ICT和ICT造成的-> TICT可能是造成缓慢衰减时间的原因。在C500-（MeOH）（3）配合物的激发态下，氢键NH中心点中心点中心点OH的增强和氢键N中心点中心点中心点HO的减弱可以促进ICT的制备将7-NHEt基团连接到CF3基团上，并在与MeOH的氢键中诱导形成TICT状态。总之，实验和理论结果表明C500在Diox和MeOH溶剂中表现出异常的失活机理。

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