A new optical doping method toward molecular electronics

Molecular materials have been recently spotlighted as promising candidates for advanced functional materials. We have developed a novel and simple doping method for a molecular material which utilizes a light-induced solid state reaction. The electrical behavior of a single crystal of a molecular charge-transfer salt of silver(I) ion qualitatively becomes differed after illumination with ultraviolet-visible (UV-VIS) light. The X-ray photoelectron spectroscopy also demonstrated that there was neutral silver species concentrated in the illuminated part of the pressed pellet sample, while only silver (I) ions were detected in the rest part and non-illuminated samples. Raman spectra of the pressed pellet sample showed that the formal charge of the constituent organic π-acceptor molecule, which is responsible for the conductivity of this material, varied in accordance with the time of illumination. Illumination with UV-VIS light upon only half of a thin single crystal of the same material transformed it to junction structure, exhibiting a rectifying character. This doping method has opened a new way for fabrication of devices from molecular solids.