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  Corresponding author: tnaito@sci.hokudai.ac.jp 2 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.

We have recently found that organic conductors Ag(DR) 2 (DR = 2,5-disubsituted-N,N 0 -dicyanoquinone diimine; substituent (R) = CH 3 , Cl, Br, I) irreversibly vary their electrical and magnetic properties by UV irradiation. By selecting the irradiation conditions (wavelengths, temperature, atmosphere, duration), one can accurately control the physical properties from metallic to insulating behavior while retaining their crystal structures. In order to clarify the mechanism of the conductivity change in the case of R = Cl, Br, and I, structure analysis of the irradiated crystals has been carried out. Transmittance electron microscopy and X-ray single crystal structure analysis clarified that the Ag(DCl) 2 crystals after 72 h irradiation (375 nm) contained single crystals of nearly three-dimensionally ordered AgCl (0.9 in mole fraction) with varying dimensions (∼1-50 nm). Owing to such a unique hybrid crystal structure, a highly nonlinear current-voltage characteristic unlike any existing electronic devices is observed on irradiated single Ag(DCl) 2 crystals.