Study of the Spin Alignment in the Photo-Excited States of Organic High-Spin Molecules and Magnetic Polymers

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This project has been carried out in order to clarify the electronic states and the spin alignment on the photo-excited states of multi-spin open-shell organic molecules in which the spin correlation among the unpaired spins exists. We have succeeded to construct a high-sensitivity zero-field optically detected magnetic resonance apparatus (ODMR) which is very useful and dispensable to study the excited spin states. We have synthesized several model compounds for the study of their ground and excited spin states. I have investigated the magnetic and optical properties of a series of thioaminyl radical crystals, stable nitronylnitroxide radicals and the spin alignment of the organic high-spin molecules. The tree stable thioaminyls show ferromagnetic behaviors described using the one-dimentional Heisenberg model with the large ferromagnetic interaction of 2J/kbeta = 28.0, 11.4 and 3.6 K.The low-temperature susceptibility and heat capacity measure-ments of the crystal showing 2J/kbeta = 2 … More 8.0 reveals a magnetic phase transition at 0.4 K.For the unique organic high-spin molecule, 4T4'Q-ether, a quantum spin contraction phenomena has been discovered in its triplet ground state with, low-lying quintet and septet excited states. Using the above-mentioned ODMR apparatus and low-temperature optical spectroscopy, We have studied the photo-excited spin states of these compounds. We have succeeded to detect the phosphorescence spectra for biphenyl-3,3'-bisphenylmethylene, naphthalene-nitronylnitroxide radical, and Br-substituted, pyrene-nitronylnitroxide radical. This finding indicates that the existence of the photo-excited high-spin (S<greater than or equal>3/2) states, leading to the determination of the location of the excited high-spin states above the ground states. An ODMR spectrum was observed for Br-substituted pyrene-nitronylnitroxide radical. The detail study of the photo-excited high-spin state is in progress. The problems of the low efficiency of the intersystem-crossing and a strong spin forbidden effect between the excited doublet and excited quartet states were revealed. These findings lead to an important research subject for "the photo-excited spin science and spin chemistry". We also find out a clue to solving the low-efficiency intersystem crossing problem by the heavy atom substitution. The detail study of the titled research subject is now going in progress. This project has lead to a new development in the field of the spin chemistry as well as revealing the problem of the strong spin forbidden between the excited doublet and quarte Less