INFLUENCE OF SILVER CATIONS ON THE FLUORE SCENCE PROPERTIES OF POLYCYCLIC AROMATIC-HYDROCARBONS

Combining the results of fluorescence and triplet-triplet absorption m easurements, the influence of silver perchlorate on the excited states of pyrene, phenanthrene, 9-cyanophenanthrene, 9,10-diphenylanthracene and 9,10-dicyanoanthracene in fluid solutions has been investigated. In correspondence with a small energy gap between the lowest excited s inglet state and the nearest lower triplet state an external heavy ato m effect has been found to be responsible for the fluorescence quenchi ng in the case of pyrene, phenanthrene and 9-cyanophenanthrene. In the case of 9,10-diphenylanthracene and 9,10-dicyanoanthracene, where thi s energy gap is large, an exciplex emission is observed with no signif icant increase of triplet state formation. Furthermore, 9-cyanophenant hrene and 9,10-dicyanoanthracene under similar experimental conditions form ground state complexes with AgClO4 with a red-shifted fluorescen ce. From time-resolved fluorescence measurements a dynamic equilibrium of association in the excited state is deduced.