EFFECTS OF HIGH MAGNETIC-FIELD ON THE LIFETIME OF CHAIN-LINKED TRIPLET BIRADICALS COMPOSED OF XANTHONE KETYL AND XANTHENYL RADICALS

The magnetic field dependence (0-13.1T) of the lifetime of the chain-l inked triplet biradicals, composed of xanthone ketyl and xanthenyl rad icals, has been studied as a function of chain length. Upon increasing a magnetic field, its lifetime increases steeply to the respective ma ximum value at ca. 2 T. Upon further increasing the field, the lifetim e of a long chain biradical decreases slightly, whereas those of all o ther biradicals are almost constant. Chain length dependence of the bi radical lifetimes in a low magnetic field (0.1 to ca. 2 T) are discuss ed in terms of the spin-lattice relaxation (SLR) due to the dipole-dip ole interaction between two radicals and the spin-orbit-induced inters ystem crossing from triplet states of biradicals. A slight decrease in the lifetime, observed for a long chain-linked biradical in high magn etic field, is explained by the SLR due to the anisotropic Zeeman inte raction.