The dissociation processes of excited states in vapor-deposited thin films of N,N'-dimethylperylene-3,4,9,10-dicarboximide (Me-PTCDI) and 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) are investigated in detail by means of electric field induced fluorescence quenching and photoresponse. The decay mechanisms of the two materials are quite different: Time resolved field induced fluorescence quenching on Me-PTCDI shows rate type quenching. Two spectral ranges with different field dependencies and decay times were observed. An efficient dissociation requires external fields of up to 2 x 10(6) V/cm. In PTCDA films, the quenching is of both rate and amplitude type. For this material, two spectral ranges with different field dependencies are recorded. A field induced luminescence enhancement is measured in the range between 520 and 600 nm. The combination of the fluorescence quenching measurement with the relative photoresponse and absolute luminescence quantum yield of Me-PTCDI allows to estimate the decay rate constants of the visible states of Me-PTCDI. (C) 2000 Elsevier Science S.A. All rights reserved.