Electron paramagnetic resonance absorption in oriented phosphorescent chrysene at magnetic fields below 125 G. II. Multiple orientation of chrysene triplets in p-terphenyl single crystals

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Abstract
Multiple electron paramagnetic resonance absorptions by phosphorescent chrysene‐d12 in single crystals of p‐terphenyl‐h14 have been investigated at static magnetic fields below 50 G and at ∼77°K. It has been demonstrated that the observed multiplet structure (corresponding to seven triples of zero‐field transitions) arises from multiply oriented chrysene‐d12 triplet states. Four types of experiments giving qualitative and quantitative information concerning these multiple orientations are characterized, and results from each type are presented. The orientations of the inequivalent chrysene‐d12 triplet magnetic fine‐structure tensor axes with respect to each other and to the p‐terphenyl molecular and crystal axes have been quantitatively determined from data presented here and previously [R. E. Gerkin and A. M. Winer, J. Chem. Phys. 56, 1359 (1972)]. The dihedral angle between the two translationally inequivalent triplets required by the host structure for each of the seven sets of guests ranges from 50° to 58°, in contrast to the dihedral angle of 69° for the host p‐terphenyl. The various chrysene‐d12 triplet tensorial axes are oriented to within ∼5°–∼15° of the corresponding host reference axes and, somewhat surprisingly, these three tensorial axis sets (A, B, C) show magnitudes of misalignment comparable to each other.