'Excimer’ fluorescence III. Lifetime studies of 1:2-benzanthracene derivatives in solution

Abstract Observations were made of the fluorescence lifetimes of 1:2-benzanthracene and fourteen of its methyl derivatives in dilute deoxygenated cyclohexane solutions. 1:2-benzanthracene and its 5-, 6- and 10-methyl derivatives were also studied in more concentrated solutions. The time response functions of the monomer and excimer fluorescence components were measured by two independent methods, namely the phase and modulation fluorometer and the pulsed light source techniques. The quantum efficiency of the monomer fluorescence in dilute solutions, and the relative excimer/monomer fluorescence yield IDIM in concentrated solutions, were also observed. The results are analyzed to determine the rate parameters of monomer and excimer fluorescence and of excimer formation and dissociation. It is found that only about half the collisions between excited and unexcited monomers result in excimer formation. This behaviour differs from that of pyrene and it is indicative of weaker excimer interaction in the 1:2-benzanthracene derivatives. The factors determining IDIM are discussed.