This brief article describes the content of the June 2002 issue of MRS Bulletin focusing on Electroactive Organic Materials. These materials are now being considered as the active components in displays, electronic circuits, solar cells, chemical and biological sensors, actuators, lasers, memory elements, and fuel cells. The flexibility of their molecular design and synthesis makes it possible to fine-tune the physical properties and material structure of organic solids to meet the requirements of technologically significant applications. In contrast to inorganic materials, active organic thin films can be deposited at much lower substrate temperatures (less than 120°C) in low-vacuum or atmospheric-pressure environments. It has been demonstrated that low-cost deposition techniques such as solution spin-coating, casting, and even printing can be used for the deposition of solution-soluble organic materials. These processing advantages, together with the natural abundance of organic solids, make electroactive organic materials attractive for large-area and low-cost applications.

The ability of excited states (excitons) to migrate rapidly and efficiently through conjugated polymers makes these materials ideal for use in sensors based on fluorescence quenching or amplification of fluorescence signals. The structural features we are able to introduce into these polymers have allowed us both to design highly sensitive fluorescent sensors for specific analytes, such as the explosive trinitrotoluene (TNT), and to create assemblies that control energy transfer along a predetermined path. The principles involved have broad utility in the design of sensory materials as well as of electronic devices and display components based on electronic polymers.

Conjugated light-emitting polymers (LEPs) have real potential to serve as the active layer in a new generation of emissive displays. Emerging as lead candidates for first-generation displays are poly(1,4-phenylene vinylene)s (PPVs) and poly(9,9-dialkylfluorene)s, as well as other polyaromatic materials. The poly(fluorene)s are at present the most commercially developed of these LEP materials for red–green–blue (RGB) applications. The low power consumption of LEP devices in general makes them particularly suited to mobile applications. Combining solution-processable emissive polymers with direct-patterning methods such as ink-jet printing will lead to the possibility of low-cost, high-resolution displays. The synthesis and properties of PPVs and poly(9,9-dialkylfluorene)s are briefly reviewed in this article, with a major focus on recent developments.

This article focuses on self-assembled photovoltaic materials based on a new class of semiconducting block copolymers for application in photovoltaic devices. Topics discussed include the materials concept for efficient photovoltaic-device structures, their macromolecular design and synthesis, and their performance in relation to their molecular, mesoscopic, and interfacial structures. An ideal organic material for this application would have to compete with amorphous silicon in regard to energy-conversion efficiency and fabrication costs. The potential of the semiconducting block copolymers presented in this review lies in the promise of large-area, mechanically flexible, self-structured photovoltaic devices fabricated by inexpensive processing techniques.

The development of new conjugated-polymer tools for the study of the biological realm, and for use in a clinical setting, is reviewed in this article. Conjugated-polymer actuators, based on the changes of volume of the active conjugated polymer during redox transformation, can be used in electrolytes employed in cell-culture media and in biological fluids such as blood, plasma, and urine. Actuators ranging in size from 10 μm to 100 μm suitable for building structures to manipulate single cells are produced with photolithographic techniques. Larger actuators may be used for the manipulation of blood vessels and biological tissue.