ABSTRACT
Carbocations play important roles as intermediates in organic chemistry. Stable and metastable ions are formed in acidic media [1] and since the lifetime of these intermediate species is oen very short, time-resolved spectroscopy on the order of fs-ns is used to detect them. For this purpose, carbocations must be generated by laser impulses or lamp ashes of shorter duration than the time resolution of the spectroscopic equipment. A common method of photochemical carbocation generation is heterolytic bond ssion of C-X bonds, whereby X is an electron-withdrawing group with proper nucleofuge properties [2]. Heterolytic photocleavage is favored in solvents of high polarity and with compounds yielding cations with low pKR+ values and having leaving groups X− with low pKa values for the conjugate acid. While the photoreaction may start from either the excited singlet or triplet state, singlet states are most oen involved. ˆe pathways of the photoreactions di‰erentiate between adiabatic or diabatic bond ssions. ˆe diabatic photoreaction is the dominant process, but in some cases, indications of the generation of excited carbenium ions were found [3,4]. In general, the eŽciency of the photoheterolysis is high, resulting in high quantum yields [2].
