Role of Contact and Solvent-Separated Radical Ion Pairs in the Diffusional Quenching of trans-Stilbene Excited Singlet State by Fumaronitrile

Article abstract of DOI:10.1021/j100201a045

Picosecond absorption spectroscopy is used to examine the question of wether contact radical ion pairs (CRIP) or solvent-separated radical ion pairs (SSRIP) are formed upon the quenching, by electron transfer, of the first excited singlet state of trans-stilbene (S₁) by fumaronitrile (FN).Prior to these experiments, it was generally believed that for exothermic reactions in polar solvents, SSRIP are formed upon quenching by electron transfer.However the present experiments reveal that the quenching of S₁ by FN in acetonitrile leads to the formation of CRIP.To establish the nature of the radical ion pair formed upon electron transfer, the kinetics for the decay of the CRIP and the SSRIP are established.