Photochemical modification of magnetic properties in organic low-dimensional conductors

Magnetic properties of organic charge transfer salts Ag(DX)2 (DX=2,5-dihalogeno-N,N′-dicyanoquinonediimine; X=Cl, Br, I) were modified by UV irradiation from paramagnetism to diamagnetism in an irreversible way. The temperature dependence of susceptibility revealed that such change in magnetic behavior could be continuously controlled by the duration of irradiation. The observation with scanning electron microprobe revealed that the original appearance of samples, e.g. black well-defined needle-shaped shiny single crystals, remained after irradiation irrespective of the irradiation conditions and the duration. Thermochemical analysis and X-ray diffraction study demonstrated that the change in the physical properties were due to (partial) decomposition of Ag(DX)2 to AgX, which was incorporated in the original Ag(DX)2 lattices. Because the physical properties of low-dimensional organic conductors are very sensitive to lattice defects, even a small amount of AgX could effectively modify the electronic properties of Ag(DX)2 without making the original crystalline appearance collapse.