Fluorescence properties of fluorenone and fluorenone molecular clusters with solvent molecules formed in a supersonic free jet expansion were studied. It revealed that fluorenone in the molecular cluster with acetonitrile emits strong fluorescence from its pipi* singlet state while fluorescence from bare fluorenone is very weak. Furthermore, no evidence of intracluster hydrogen abstraction to form ketyl radical in the cluster with 1,4-cyclohexadiene was observed. The fluorenone-ethanol cluster has considerably short lifetime of the S-1 state. It could be attributed to the fact that the hydrogen bond in the molecular clusters should accelerate the nonradiative process. (C) 2002 Elsevier Science B.V. All rights reserved.