Effect of high magnetic field on the lifetime of biradicals generated frombenzophenone and diphenylamine bifunctional chain molecules

effect of high magnetic fields (less than or equal to 13 T) on the lifetime of triplet biradicals (BPH.-O-(CH2)(n)-O-DPA(.), n = 2, 4, 8, 16) composed of a protonated diphenylketyl radical (BPH.) and a diphenylaminyl radical (DPA(.)) is studied in N,N-dimethylformamide at room temperature by laser f lash photolysis. On increasing the magnetic field from zero to ca. 2 T, the lifetime of BPH.-O-(CH2)(n)-O-DPA(.) (n = 4, 8, 16) increases steeply, and then decreases gradually in higher magnetic fields. The lifetime of BPH.-O -(CH2)(2)-O-DPA(.) decreases gradually with increasing the magnetic field w ith a shallow dip at ca. 2 T. The reversal of the effect observed in the li fetime of BPH.-O-(CH2)(n)-O-DPA(.), n = 4, 8, 16 is interpreted in terms of spin-lattice relaxation which is induced by the anisotropic Zeeman interac tion. The dip observed in the magnetic held dependence of the lifetime of B PH.-O-(CH2)(2)-O-DPA(.) is attributable to the S-T- level crossing.