对—卤代苯乙酮光诱导短时动力学研究

【作者】 董晓慧；

【导师】 张树东；

【作者基本信息】 曲阜师范大学 ， 物理电子学， 2009， 硕士

【摘要】 本文采用共振拉曼光谱技术研究了对-卤代苯乙酮在乙腈溶液中光诱导电子转移在Franck-Condon区域的短时动力学的特征,并结合密度泛函理论计算方法讨论了苯乙酮、对氟苯乙酮、对氯苯乙酮、对溴苯乙酮、对碘苯乙酮光化学反应在微观反应动力学上的调控因素,在一下几个方面做出了贡献:（1）测得苯乙酮、对氟苯乙酮、对氯苯乙酮、对溴苯乙酮、对碘苯乙酮在乙腈溶液中的最大吸收带分别在238nm、241nm、248.4nm、252.4nm、261.8nm左右。最大吸收位置的偏差取决于溶剂与其形成氢键能力的大小。（2）获得对-卤代苯乙酮的共振拉曼光谱,进行了强度分析。研究结果表明,对-卤代苯乙酮在乙腈溶液中的共振拉曼光谱具有一定的共同的特征:在乙腈溶液中Franck-Condon区域的短时动力学具有多维性,主要沿着苯环C-C伸缩振动、C=O伸缩振动。有关苯环振动的振动重组能占总振动重组能的50%以上,羰基的振动重组能约占20%,说明在光诱导电子转移的过程中苯环C-C键和羰基的几何结构发生较大程度的调整。（3）对-卤代苯乙酮大部分振动模的描述以及拉曼位移量相似。对位H被卤素F,Cl,Br,I取代后,出现了Ph-CO-CH3伸缩振动和苯环变形振动模（苯乙酮中相对应的是苯环的三角振动）,这个振动模式在对碘苯乙酮中没有出现;在对氟苯乙酮、对氯苯乙酮、对溴苯乙酮的拉曼位移分别出现了183cm^-1、240cm^-1、256cm^-1的蓝移现象。（4）对-卤代苯乙酮的反应坐标和振动重组能明显不同。反应坐标|Δ|最大的是对氟苯乙酮,其次是对溴苯乙酮;总的振动重组能也明显不同,其中,对氟苯乙酮具有最大的振动重组能1780cm^-1,这说明对氟苯乙酮更容易发生分子间激发,具有更高的势能面。对碘苯乙酮振动重组能相对于其它总振动重组能要小,在Franck-Condon区域和内转换过程中经历了更小的几何结构重组,使得对碘苯乙酮的激发态分子更趋向稳定。而对溴苯乙酮的振动重组能并没有如预料的那样比对氯苯乙酮的低。（5）苯乙酮、对氟苯乙酮、对氯苯乙酮、对溴苯乙酮、对碘苯乙酮的非均质展宽（G）分别为700 cm^-1、700 cm^-1、750 cm^-1、650 cm^-1、1400cm^-1,均质展宽（Γ）分别为500 cm^-1、350cm^-1、500 cm^-1、500 cm^-1、500cm^-1。对碘苯乙酮的非均质展宽表现出与其它几个化合物不同的溶剂效应。激发态物种的衰变对均质展开的贡献可以由它的激发态寿命来决定。显然,对氟苯乙酮的具有最小的激发态寿命。（6）苯乙酮对位H被卤素F,Cl,Br,I取代后,不仅调整了Franck-Condong区域的短时反应动力学特征,而且引起了各个振动模能量分配发生改变。更多还原

【Abstract】 In this paper,we have studied the short-time photodissocciation dynamics of photo-induced Charge-Transfer of p-halogenated acetophenone in acetonitrile solution by the Resonance Raman spectra combined with DFT calculation and discussed the influential factors to tune the photochemical reactions.Main contributions of the present work are summarized as follws,（1） We obtained the absorption spectrum of acetophenone,p-fluoroacetophenone, p-chloroacetonphone,p-bromoacetophone,p-Iodoacetophenone in acetonitrile solution which has a charge-transfer band near 238nm,241nm,248.4nm,252.4nm,261.8nm,respectively.The hydrogen bonding is one key factor affecting the different charge-transfer band.（2） We obtained the Resonance Raman spectras of p-halogenated acetophenone,and Resonance Raman analyses were done,respectively.The results indicate that the Resonance Raman spectras of p-halogenated acetophenone have the similar characters:the Franck-Condon region short-time photodissocciation dynamics of p-halogenated acetophenone have multidmensional characters with motion predominantly along the nominal ring C-C stretch,C=O stretch.The vibrational organizational energy of benzene ring is more than 50%,The vibrational organizational energy is about 20%.This shows during the process of potoinduced charge-transfer,the C-C of benzene ring and C=O have great change.（3） Most of the vibrational modes and frequency of p-halogenated acetophenone are similar. Hovever,after the substitution of H_p atom by the F,Cl,Br,I,there is a new mode:Ph-CO-CH3 stretch and ring deformation mode（which in acetophenone is benzene trigonal bend）.The mode is 183cm^-1,240cm^-1,256cm^-1 blue shift in p-fluoroacetophenone,p-chloroacetonphone, p-bromoacetophone,respectively.（4） The reaction coordinate and vibrational organizational energy of p-substituted acetophenone are different.The largest of reacion coordinate |△| is p-fluoroacetophenone,then is p-bromoacetophone.P-fluoroacetophenone have the largest total vibrational organizational energy,1780 cm^-1,which shows p-fluoroacetophenone is more easily excited and have higher potential energy surface,The vibrational organizational energy of p-Iodoacetophenone is the smallest.This shows that p-Iodoacetophenone have smaller geometric structure recombination at the Franck-Condon region and during the internal coversion,which made the excited more stable. Moreover the vibrational organizational energy of p-bromoacetophone is not smaller than p-chloroacetonphone.（5） The inhomogeneous broadening of acetophenone,p-fluoroacetophenone, p-chloroacetonphone,p-bromoacetophone,p-Iodoacetophenone are 700 cm^-1,700cm^-1,750cm^-1, 650 cm^-1,1400cm^-1,respectively.The homogeneous broadening is 500 cm^-1,350cm^-1,500 cm^-1, 500 cm^-1,500cm^-1,respectively.The inhomogeneous broadening of p-Iodoacetophenone have different effects of solvation from other compounds.Obviously,the p-fluoroacetophenone’s life of excited state is the smallest.（6） We have noted that the substirution of the H in acetophenone by F,Cl,Br,I effectively modulates the Franck-Condon region dynamics and the nergy partioning among the varous vibrational degrees.更多还原