Optical nuclear polarization as a consequence of the non-crossing rule (Level-Anti-Crossing): III. Experimental results and evidence for guest-host complexes in doped fluorene crystals

Fluorene crystals doped with the guest molecules acridine, phenazine and anthracene have been studied before due to their strong Optical Nuclear Polarization (ONP) in low magnetic fields around 100 gauss. In this paper, these results together with supporting new data are interpreted in terms of ONP as a consequence of Level-Anti-Crossing (LAC) within the excited triplet state of a guest-host complex. The results permit a first detailed check of the theoretical model of ONP by LAC including the influence of electronic relaxation. Furthermore, they render the spectroscopic parameters needed for the characterization of the triplet-state complexes: -The zero-field splitting tensor and the orientation of its principal axes system with respect to the crystalline axes. -The proton hyperfine tensor, which is essentially due to one-proton spin in the CH2-group of the fluorene host molecule contributing to the complex