Singlet exciton migration in a random organic two-component system containing physical and chemical traps

Steady-state as well as time-dependent fluorescence studies have been carried out near 80 K on glassy mixed layers of anthracene and phenanthrene doped with tetracene and containing incipient anthracene dimers as physical traps. The efficiency of energy transfer from initially excited anthracene (“donor”) sites to tetracene (“supertrap”) has been measured as a function of donor concentration c_D. The results are interpreted in terms of a superposition of two transfer pathways: (i) Random walk of excitons across the donor ensemble to either tetracene or anthracene dimers and (ii) single step Förster transfer from the excited dimers (excimers) to tetracene. The efficiency of process (i) is in quantitative accord with the predictions of the 3D version of the Loring, Anderson and Fayer theory assuming dipole-dipole coupling.