No abstract

Com bining the results o f fluorescence and triplet-triplet absorption measurements, the influence o f silver perchlorate on the excited states o f pyrene, phenanthrene, 9-cyanophenanthrene, 9,10-diphenylanthracene and 9,10-dicyanoanthracene in fluid solutions has been investigated. In corre spondence with a small energy gap between the lowest excited singlet state and the nearest lower triplet state an external heavy atom effect has been found to be responsible for the fluorescence quenching in the case o f pyrene, phenanthrene and 9-cyanophenanthrene. In the case o f 9,10-diphenylanthracene and 9,10-dicyanoanthracene, where this energy gap is large, an exciplex emission is observed with no significant increase o f triplet state formation. Furthermore, 9-cyanophenanthrene and 9,10-dicyanoanthracene under similar experimental conditions form ground state complexes with A gC 104 with a red-shifted fluorescence. From time-resolved fluorescence m easurements a dynamic equilibrium o f association in the excited state is deduced.

Ins titu t fur Ph ysika lisc h e u n d Th eore tisc h e Ch em ie, Tech n isch e Un ivecsita t Bra unsch weig, 0-38 I 06 Bra unsc h weig, Germany kFThe determination of kinetic and standard thermodynamic parameters (reorganization energies, electronic coupling elements, free energy, enthalpy and entropy changes) of intramolecular photoinduced charge separation reactions in cl>-(IO-Phenyl-9-anthryl)propiophenone f r o m the analysis of biexponential fluorescence decay curves exhibits distinct differences between the electronic factors in aprotic (benzene, acetonitrile, and mixtures thereof) and protic (methanol, ethanol) solvents and an unexpectedly small variation of the standard free energy change with solvent p o I a rity.