We study photoluminescence and triplet-triplet exciton annihilation in a neat film of a fac-tris(2-phenylpyridyl)iridium(III) $\left[\mathrm{Ir}{\left(\mathrm{ppy}\right)}_3\right]$-cored dendrimer and in its blend with a $4,4^{\prime }$-bis($N$-carbazolyl)biphenyl host for the temperature range of $77–300\mathrm{K}$. The nearest neighbor hopping rate of triplet excitons is found to increase by a factor of 2 with temperature between 150 and $300\mathrm{K}$ and is temperature independent at lower temperature. The intermolecular quenching rate follows the Arrhenius law with an activation energy of $7\mathrm{meV}$, which can be explained by stronger dipole-dipole interactions with the donor molecule in the higher triplet substate. The results indicate that energy disorder has no significant effect on triplet transport and quenching in these materials.

• Received 28 June 2007

DOI:https://doi.org/10.1103/PhysRevB.77.085211