Fluorescence quenching of pyrene monomer and excimer by CH3I

The fluorescence quenching rate constants of pyrene monomer and excimer by CH3I were obtained at several temperatures in methylcyclohexane. Both quenc hing processes are kinetically controlled, allowing insight on the mechanis m of quenching. The rate constants have both temperature-independent and te mperature-dependent components. The temperature-independent component for b oth monomer and excimer fluorescence is consistent with quenching due to en hanced intersystem crossing to a lower energy triplet stare. The monomer te mperature-dependent component comes from the enhancement of the intersystem crossing to a higher energy triplet state. The thermally activated excimer quenching is associated with the excimer dissociation step to give a pyren e in a second tripler state plus a ground state pyrene molecule. (C) 2001 E lsevier Science B.V. All rights reserved.