离子液体[bmim][BF_4]对联苯甲酰光化学反应影响的瞬态吸收光谱

Transient Absorption Spectroscopy of the Effects of the Ionic Liquid [bmim][BF_4] on the Photochemical Reactions of Benzil

利用纳秒级激光光解瞬态吸收光谱研究了联苯甲酰(BZ)在离子液体1-丁基-3-甲基咪唑四氟硼酸盐([bmim][BF4])与乙腈(MeCN)混合体系中的光化学反应行为.考察了探针分子BZ存在下[bmim][BF4]/MeCN比例对体系中化学反应动力学的影响.实验发现:在N2饱和条件下,BZ溶液经激光辐照后产生的激发三线态3BZ*遵循一级反应动力学规律衰减.离子液体(IL)相对比例增加对3BZ*瞬态吸收峰的位置和强度没有产生明显影响.但离子液体体积分数VIL的变化对[bmim][BF4]/MeCN混合溶剂中光诱导电子转移的影响却非常显著,总体上电子转移产生的自由基的表观生成速率常数kgr随[bmim][BF4]的VIL增大而减小.在[bmim]BF4]比例足够大的情况下,3BZ*与三乙胺或四甲基对苯二胺之间的电子转移被抑制.

Using benzil （BZ） as a probe molecule, the photochemical properties of the ionic liquid （IL） 1-butyl-3-methylimidazolium tetrafluoroborate （[bmim][BF4]） and its binary mixed solutions with acetonitrile （MeCN） were investigated by nanosecond laser photolysis. We found that the decay of the triplet excited state of benzil （3BZ＊） in a N2-saturated solution followed mono-exponential kinetics. Along with the increase in the volume fraction （VIL） of [bmim][BF4] in the mixed solvents, the absorption peak of 3BZ＊ did not change. However, the effect of different VIL values on the photoinduced electron transfer process in the mixture of [bmim][BF4]/MeCN was obvious. Moreover, the apparent rate constant （kgr） of the formed radical decreased obviously with an increase in VIL. When the ratio of [bmim][BF4] was sufficiently high, the electron transfer reaction between 3BZ＊ and triethylamine or N,N,N′,N′-tetramethyl-p-phenylenediamine was retarded.