Both steady-state and time-resolved studies in acetonitrile (ACN) solutions show that the excited singlet (S-1) states of calixarenes (CX) undergo quenching by chloroalkanes (CA). It has been revealed by characterizing the Cl ions in the photolyzed CX-CA systems in ACN solutions that the quenching occurs due to dissociative electron transfer (DET) mechanism, whereby a C-Cl bond of the CAs undergoes dissociation on acceptance of an electron from excited CX. The bimolecular quenching constants (k(q)) in the present systems were correlated with the free energy changes for the concerted DET reactions based on a suitable DET theory. Such a correlation results in the recovery of an intramolecular reorganization energy, which is substantially lower to account for the C-Cl bond dissociation energy of the CAs. Comparing present results with those of an another donor-acceptor system (e.g., biphenyldiol-CA systems) where a concerted DET mechanism is applicable, it is inferred that in CX-CA systems both concerted and stepwise DET mechanisms operate simultaneously. It is proposed that the interaction of excited CXs with encaged CAs follows the stepwise mechanism whereas that with the out of cage CAs follows the concerted mechanism.