No abstract

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.