Photochemistry of Bifunctional Chain Molecules Containing Benzophenone and Anilino Chromophores. Magnetic Field and Magnetic Isotope Effects on Lifetimes of Triplet Biradicals

The decay time of biradicals containing a benzophenone ketyl and an anilino-alkyl radical has been examined by nano-second laser photolysis in the presence of external magnetic fields up to 1 T. When sites with high spin densities are labeled with heavy carbon, noticeable magnetic isotope effects are observed on the decay kinetics for biradicals. Small kinetic effects are observed for deuterated species. The obtained results can be interpreted in terms of spin-lattice relaxation due to anisotropic hyperfine and dipole–dipole interactions. Procedures for preparing labeled species are also described.