Formation of excited states in the pulse radiolysis of solutions of aromatic compounds in cyclohexane and benzene

Abstract

Measurements have been made on the triplet absorptions produced on irradiation of solutions in cyclohexane and benzene. Triplet yields were determined using the most recent extinction coefficient estimates. The yields were: anthracene; in cyclohexane, G= 0.2 (10^–4 M) to G= 1.05 (10^–2 M); in benzene, G= 0.15 (10^–4 M) to G= 1.5 (5 × 10^–3 M). Naphthalene; in cyclohexane, G= 0.25 (10^–4 M) to G= 2.4 (9 × 10^–1 M); in benzene, G= 0.4 (10^–3 M) to G= 2.3 (1 M). Benzophenone; in cyclohexane (ketyl radical); in benzene, G= 0.4(10 ^–3 M)to G= 2.3 (1 M). Benzophonone; in cyclohexane (ketyl radical); G= 0.4 (10 ^–4 M) to G= 4.8 (1 M); in these solutions. Dilute nepthalene in cyclohexane and benzene gave monomer fluorescence but at higher concentrations emission due to excimer was also seen. Allowing for excimer formation, the concentration dependence of fluorescence in cyclohexane was similar to that of the triplet states. In benzene the rise in napthalene fluorescence was less than the rise in triplet yield.

For cyclohexane solutions, solute triplet states are believed to be formed mainly through neutralization of solute ions, some directly, and some via the intermediate formation of solute singlet states. A similar mechanism may operate in concentrated solutions in benzene, but in dilute solutions, solute triplets may also be formed via singlet and triplet states of the solvent.