The triplet state energies of rubrene and diphenylisobenzofuran

Abstract

Until now controversies have arisen from the estimates of the triplet energies of rubrene (R) and diphenylisobenzofuran (DPBF), both of which are known reactants with singlet oxygen. To clarify the situation, flash kinetic spectroscopy was used to measure rates of energy transfer between these two molecules and other energy donor and energy acceptor molecules of known triplet energy. The lowest excited triplet state in R is nearly isoenergetic with the corresponding state in zinc phthalocyanine, and the energy value assignment is 9.2 ± 0.2 kilokaysers. Triplet—triplet annihilation is thermoneutral and is consistent with the lowest triplet state having approximately one-half the energy of the lowest excited singlet state. Based on the rates at which azulene and ferrocene quench the lowest excited triplet state of DPBF, the energy of this state can be assigned a value of 11.9 ± 0.1 kilokaysers.