Effect of High Magnetic Field on the Lifetime of Biradicals Generated from Benzophenone and Diphenylamine Bifunctional Chain Molecules

Abstract

Abstract The effect of high magnetic fields (≤ 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 flash 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 with a shallow dip at ca. 2 T. The reversal of the effect observed in the lifetime 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 interaction. The dip observed in the magnetic field dependence of the lifetime of BPH·-O-(CH2)2-O-DPA· is attributable to the S-T_ level crossing.