Dye-Sensitized Molecular Charge Transfer Complexes: Magnetic and Conduction Properties in the Photoexcited States of Ni(dmit)2 Salts Containing Photosensitive Dyes

Photosensitive dyes often induce charge transfer (CT) between adjacent chemical species and themselves under irradiation of appropriate wavelengths. Because of the reversibility and selectivity of such CT, it is considered to be interesting to utilize such dyes as optically controllable trigger components for conduction and magnetism in the photoexcited states of organic materials. Based on this idea, such a type of new salts, i.e., gamma- and delta-DiCC[Ni(dmit)(2)] in addition to DiCC(2)[Ni(dmit)(2)](3) have been prepared, characterized and their physical and structural properties have been examined both under dark and irradiated conditions (dmit(2) = 1,3-dithiole-2-thione-4,5dithiolate, DiCC(+) = 3,3'-Dihexyloxacarbocyanine monocation). Among them, under UV (254-450 nm) irradiation, delta-DiCC[Ni(dmit)(2)] exhibited photoconductivity being six times as high as its dark conductivity at room temperature. The electron spin resonance (ESR) spectra have demonstrated that there are photoexcited spins on both DiCC and [Ni(dmit)(2)] species as a result of the CT transition between them, serving as localized spins (DiCC) and carriers ([Ni(dmit)(2)]), respectively. The results obtained in this work have indicated that the strategy mentioned above is effective in developing organic photoresponsive semiconductors with paramagnetism.