Photochemistry of aromatic compounds. Part 1.—Acid-base properties of singlet and triplet excited states of pyrene derivatives and aza-aromatic compounds

Abstract

Variations of acidity constants between the ground state G and the fluorescent state S₁ of 1-, 2-, 4- and 9-azaphenanthrenes, 1-aminopyrene, 1-hydroxypyrene and pyrene-1-carboxylic acid have been measured by application of the Förster cycle. Triplet state pK values of the same derivatives were obtained by the flash photolysis technique. For 1-hydroxypyrene under flash photolysis conditions, only one transient, whose spectrum is not pH dependent could be observed. This transient spectrum has been assigned to the pyrenoxyl radical. There appears to be no relationship between the position of protonation of the various aza-phenanthrenes and the ΔpK between the ground state and the singlet or triplet excited states.