- Halogenated Acetophenone Light-induced Short-term Kinetic Studies

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 |â–³| 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.