Energy transfer from high-lying excited states

It was found that in the benzene-CHCl3 system the G value for radical formation due to energy transfer is approximately 10. It is also shown that the G value for direct formation of the lowest excited singlet state of benzene S1 is 0,2 and the G value for overall formation os S1 is approximately 1,0. Since the G value for formation of free charges in benzene and in anthracene is 0,07 and 0,25, respectively, it is concluded that in the benzene-CHCl3 system free radicals are formed by energy transfer from upper excited states of benzene.Energy from high-lying benzene states is also transferred to phenylbiphenylyl oxadiazole (PBD), as evidenced by the reduction of free radical formation when PBD is added to the system benzene-CHCl3 under high energy excitation. The energy transfer from high-lying benzene states to PBD leads to the formation of high-lying PBD states which can also transfer to CHCl3 to form free radicals, but to a smaller extent than the high-lying benzene states. This is evidenced by the quenching of PBD fluorescence by CHCl3.Two types of dissociation processes have been found, one in which energy is transferred to the dissociating molecule and this dissociates instantaneously and another one in which after energy transfer to the dissociating molecule an excited state of finite lifetime is formed which eventually can dissociate. The first process occurs in CCl4, and CHCl3, the latter in chlorobenzene φCl when excited via the lowest excited benzene state or directly with ultraviolet ligth. Under high energy excitation, energy transfer from high-lying benzene states occurs to high-lying φCl states and these dissociate instantaneously. The lowest φCl* with finite lifetime is subject to quenching by PBD, the higher states are not