Singlet exciton fission in pure and doped anthracene

On the basis of the kinetic model by Merrifield for triplet exciton fusion in molecular crystals, we have derived an expression which describes the reciprocal process, i.e., the anisotropy of the prompt fluorescence in the presence of singlet exciton fission in a magnetic field. For the first time a thorough comparison of Merrifield’s theory with singlet exciton fission experiments is made. The theory is compared with experimental data for the case of homofission in pure anthracene crystals as well as for the case of heterofission in anthracene crystals doped with tetracene. The resulting kinetic parameters for the fission process have almost the same values as those for triplet fusion. The origin of a discrepancy between theory and experiment along certain crystallographic axes is discussed.