Laser photolysis studies on triplet-equilibrium formation in a small triplet-energy gap system

Authors:

• Minoru Yamaji,
• Katsuji Okada,
• Bronisław Marciniak,
• Haruo Shizuka

Abstract

Formation of a triplet-equilibrium between benzophenone (BP) and dibenzothiophene (DBT) was studied in acetonitrile by 355 nm laser flash photolysis. The triplet-equilibrium constant (K_eq = 1.7) was determined at 295 K as well as the absolute rate constants for triplet energy transfer from BP to DBT (k_f = 3.1 × 10⁹ M^-1s^-1) and back triplet-energy transfer (k_b = 2.0 × 10⁹ M^-1s^-1) whose ratio (k_f/k_b) was in agreement with the K_eq value. It was revealed that the triplet-equilibrium formation in the BP-DBT system was promoted by the entropy change (ΔS = 2.0 cal mol^-1 K^-1) rather than the enthalpy change (ΔH = 0.3 kcal/mol). © 1997 Elsevier Science B.V.