Photodissociation of jet-cooled o-, m-, and p-ethyltoluene and p-fluoroethylbenzene at both 193 and 248 nm was studied separately using vacuum ultraviolet photoionization/multimass ion imaging techniques. Dissociation occurs exclusively through alkyl chain C-C bond cleavage. The measured photofragment translational energy distributions at 193 nm decrease monotonically with increasing translational energy. The distributions indicate that dissociation occurs from the ground electronic state after internal conversion. However, the photofragment translational energy distributions from o-, m-, and p-ethyltoluene obtained at 248 nm contain a slow and a fast component; the ratios between these components are 1:4, 1:1.3, and 1:6, respectively. On the other hand, only the slow component was observed from p-fluoroethylbenzene at 248 nm. The fast components are attributed to the dissociation from the triplet state after intersystem crossing, and the slow components result from the dissociation in the ground electronic state. Comparison with the photodissociation of benzene and toluene and ab initio calculation has been made.