Intermolecular charge transfer in organic donor-acceptor systems for optical storage applications

Organic molecules with novel optical and electronic properties are of great potential in the development of alternable, high density, and high-speed optical memory deices (OMD) with molecular resolution. During the course of our investigations, we have observed new optical and electric properties of some organic donor-acceptor systems in solution. The result obtained with Proton Sponge (PS)/Tetracyanoquinodimethane (TCNQ) and Phenanthrene/Tetracyanoethylene (TCNE) systems are presented, as they have been observed to provide examples of two extreme cases. The separate solutions of PS and TCNQ in acetonitrile are colorless and exhibit no electric conductivity. When they are mixed, however, the color of the mixture turns green. Its optical absorption spectrum shows a new band in the wavelength region of 600 nm - 900 nm, with a relatively high peak molar absorptivity at 850 nm. The mixture also exhibits large and almost concentration independent molar conductivity, thus indicating that complete charge transfer and charge separation have occurred among all molecules in the solution. For TCNE system, although a new optical absorption band centered at 490 nm has been observed, the electric conductivity of the mixed solution remains zero. The observed complete charge transfer and charge separation, stable charge trapping, and new adsorption band with large molar absorptivity are taken as indicators for the feasibility of developing alterable, high density OMD based on organic donor and acceptor molecular.