Lifetimes and Energies of the Relaxed Triplet States of Cyclopentadiene and Tetramethylbutadiene. A Pulse Radiolysis and Pulsed Laser Study

The triplet states of cyclopentadiene and tetramethylbutadiene have been produced in benzene by pulse radiolysis. Energy-transfer experiments have established natural lifetimes of 1.7µs and 73 ns, respectively. The observation of triplet energy transfer equilibria with pulse radiolysis and pulsed laser photolysis has established a relaxed triplet energy for cyclopentadiene of 58.0 ± 0.2 kcal mol^-1, which shows that relaxation from the Franck-Condon state is negligible. An approximate “available” triplet energy of 42 kcal mol^-1 for the relaxed tetramethylbutadiene triplet has been determined. The rate constant data for energy transfer obtained by using both pulse radiolysis and pulsed laser photolysis appear totally consistent with vertical energy transfer processes only.