RADICAL PAIR FORMATION FROM EXCITED-STATES IN DOPED AROMATIC CRYSTALS .2. OPTICAL NUCLEAR-POLARIZATION (ONP) STUDIES

The use of ONP to determine absolute signs of fine and hyperfine tensor elements in excited triplet states is developed theoretically and demonstrated experimentally. Convenient ONP-rules are formulated which relate the desired signs of the tensor elements to quantities which can be extracted from the measured ONP field dependence. Application is made to the ONP originating from the radical pair triplet state formed after photochemical hydrogen abstraction from a fluorene host molecule and hydrogen transfer to an acridine guest molecule in doped single crystals. Negative fine and hyperfine tensor elements are determined and confirm the structural model of a radical pair product inferred from EPR-data. © 1979.