excited (metastable) electronic states that can be made to re-emit on command. Examples of photonic energy storage exist in the form of chemiluminescent materials, but the systems currently available are not applicable for a variety of reasons. This area of materials research requires a breakthrough that will emerge only as a result of basic research.
Displays represent another important area of organic materials research for information processing. Flat panel displays are currently based on twisted nematic liquid crystals and require at least one substrate transistor to drive each pixel. Use of surface stabilized ferroelectric liquid crystals would provide greatly increased switching speed and a wider viewing angle and would, in principle, simplify the display design. The address of each pixel would require only an orthogonal grid array, which is less demanding (and cheaper) to produce than the current method. The introduction of ferroelectric displays is limited by the instability of the surface alignment, leading to mechanical and thermal shock instability. The alignment techniques that have evolved empirically suffice for the twisted nematic liquid crystals, but they are inadequate for ferroelectrics. The alignment process, in which interactions of individual molecules with the surface give rise to bulk alignment in layers that are microns thick, is not understood. There are theories that describe the forces controlling alignment, but there is no reasonable explanation for the generation of tilt from this interaction. Yet, the stability of alignment and control of tilt are critical to a device's performance and stability. Basic research directed toward development of a molecular-level understanding of the interaction of mesogens and alignment surfaces is essential to further development of this important area.
There have been recent discoveries of anti-ferroelectric phases for display applications that are worthy of support. These phases have hysteresis that is accessible under an applied dc offset voltage that appears to provide some of the best characteristics of the ferroelectrics. The advantage of this approach is that removal of the bias voltage reportedly results in reversion to a state that is susceptible to alignment from classical surface preparation. Hence, in principle, if the display loses alignment, repair can be achieved by inducing changes in the dc potential across the cell.
Organic photo-emitting diodes also offer great promise for display applications. Major advances have been made in the use of semiconducting, polymer-based light-emitting junctions. A barrier to progress at this time is the need for reliable electrode structures that provide efficient electrical contact with the polymeric materials. Research is also needed on the nature of the properties of organic materials that render them useful as efficient electron transport media. Hole transport appears to be easily achieved in organics, but the number of materials that function as electron transport media is very limited, and these materials have been discovered largely by accident. Basic research to develop an understanding of the structural aspects of organics that allow them to mediate electron transport efficiently could have an important impact on this field.
Another area involving active organic photonic materials is that of resists for microelectronic device fabrication. Feature sizes are now in the range of a few tenths of a micron and will probably reach about two-tenths of a micron before the end of the century. This implies a need for image edge placement and control of about two-hundredths of a micron, or 200 angstroms. At these dimensions there are energy and molecular diffusion processes that can blur the placement and size of a device's features. For example, triplet