Spin-lattice relaxation and intersystem crossing in single molecules of terrylene embedded in a p-terphenyl crystal

► Single terrylene molecules in p-terphenyl crystal were studied at temperatures 5-30 K. ► Spin-lattice relaxation couples zero-field triplet spin sublevels at temperatures >15 K. ► Results suggest proximity of the S1 and T2 states and distortion from planar symmetry. ► The spin-lattice relaxation seems to be dominated by the Raman process.