Evidence for exciton fission and fusion in a covalently linked tetracene dimer

A photophysical study of the covalently linked tetracene dimer 1,4-bis(tetracen-5-yl)benzene is presented. While the dimer's steady state spectroscopy is similar to that of monomeric tetracene, it also exhibits a long-lived fluorescence signal in solution and solid polyethylene films, which is absent in the monomer. The behavior of this long-lived component as a function of temperature and oxygenation provides evidence that a small (<1%) fraction of the singlet excited states undergoes fission into two triplet states, which recombine on the order of 100 ns. A kinetic model based on this mechanism fits the fluorescence decay data quantitatively.