The bimolecular quenching rate constants of singlet oxygen ((1)O2) by cubane and cubane derivatives were determined and found to be in the order of 10(3)-10(4) M(-1) s(-1). These values represent larger values than expected for aliphatic alkanes as a model for C-H vibrational deactivation. This result is explained by the occurrence of two different deactivation mechanisms: energy transfer to cubane C-H vibrational modes and the formation of a charge-transfer complex between (1)O2 and cubane ((1)O2(*-)...cubane(*+)).