Michel F. Molaire

Synthesis of Amorphous Monomeric Glass Mixtures for Organic Electronic Applications

We report a divergent synthetic strategy and novel design concept that exploit molecular mixtures to create amorphous organic charge-transporting glasses. Using Suzuki-Miyaura cross-coupling reactions, we synthesized well-defined molecular mixtures in a single step. These solution-processable materials are noncrystalline and show good thermal and morphological stabilities. Moreover, they have robust hole and electron mobilities, which make them excellent candidate materials for organic light-emitting diodes. Our general strategy enables the facile synthesis of noncrystalline materials with well-controlled electronic properties.

Influence of melt viscosity on the writing sensitivity of organic dye-binder optical-disk recording media

The writing sensitivity of dye-binder optical recording media has been defined as the rate of change in the recording response of the medium as a function of laser power. That response was measured by the electronic readout of the recorded pits and shown to be a function of the viscosity of the binder. The variation in dye-binder media sensitivity was 98% accounted for by variations in binder viscosity and writing laser power. For nonpolymeric systems, a more general regression model was formulated using the glass-transition temperature of the recording medium as a substitute for its viscosity. Thus, for any given dye-binder system, writing sensitivity can be largely predicted from the dye T(g), the binder T(g), and their relative concentration, assuming optimum optical efficiency.

Organic Photoreceptors for Digital Electrophotography

We describe general requirements of organic photoreceptors used for electrophotographic applications. A typical organic photoreceptor consists of a charge generation layer (CGL) and a charge transport layer (CTL). The separation of the generation and transport functions has permitted the optimization of both layers in terms of sensitivity as well as device lifetime. Dual-layer and negative-charged/hole- transporting organic photoreceptors are of primary interest in device applications, which are the focus here. The spectral sensitivity, charge mobilities, and the general characteristics of charge acceptance and photoinduced discharge of these materials are discussed. In flash exposure of electrostatic latent image, reciprocity failures reduce the sensitivity of photoreceptors and are key issues associated with digital electrophotography. We discuss reciprocity failures relating to Langevin recombination and perhaps exciton-exciton annihilation at high exposure conditions. Other related issues such as latent image spread and fatigue are also discussed.

Hole photogeneration in dual-layer photoreceptors

Hole photogeneration efficiencies have been measured in a series of dual layer photoreceptors containing generation layers of a fluorinated titanylphthalocyanine (TiO(F4-Pc)). The transport layers contained different arylamine (AA) derivatives in a polycarbonate. The AA molcules were selected for differences in oxidation potential. The efficiencies are independent of wavelength and strongly dependent on the field and the composition of the transport layer. At high fields and high AA concentrations, the efficiencies approach 0.80. The results are described by a surface-enhanced exciton dissociation argument. The argument is premised on the assumption that the absorption of a photon creates a bound electron-hole pair, which diffuses to the surface of the pigment particle, where it either recombines or dissociates into a free electron hole pair through an interaction of the donor component of the transport layer. The dissociation efficiency increases with increasing oxidation potential of the donor component. The field dependence of the dissociation process is attributed to geminate recombination and described by a theory due to Onsager. Keywords: dual layer photoreceptors, geminate recombination, free carrier photogeneration

Photoelectrographic masters containing nonionic acid photogenerators

Photoelectrographic printing is a technology which utilizes photoelectrographic masters and conventional electrophotographic toners for short run printing applications. Masters based on onium salt acid photogeneration have many desirable attributes. One shortcoming, however, is their sensitivity to changes in relative humidity. We have previously reported on a class of polymeric binders which largely overcome this problem. We have now found a class of non-ionic acid photogenerators which further enhance the performance of such masters with respect to changes in relative humidity and which enable the use of a broader spectrum of polymeric binders. We examined representative compounds from several classes of non-ionic acid photogenerators. The best results were obtained with sulfonate esters of N- hydroxyimides. Standard polycarbonate or polyester-based formulations containing these compounds along with a near-UV sensitizer exhibit contrast potentials near 90% of the initial surface potential upon exposure with a 500-W mercury arc lamp. This contrast potential remains nearly constant over the range of 30-70% relative humidity.