Zeeman Populations of Optically Produced Triplet Excitons in Anthracene

The steady‐state Zeeman populations of optically produced triplet excitons in crystalli e anthracene are obtained for a localized diffusional model. The transition rates among the Zeeman sublevels induced by exciton motion between the two anthracenes, with differently oriented dipolar principal axes, in a unit cell are calculated for an arbitrarily oriented static magnetic field. Triplet exciton motion maintains uniform high‐field sublevel populations even in the limit $\text{T\hspace{0.17em}→\hspace{0.17em}0}$ , thus explaining qualitatively several low‐temperature experiments on the delayed fluorescence from collisions of free and trapped excitons. Triplet exciton motion is also shown to account for spin–lattice relaxation at room temperature.