Optoelectronics: Combining chemical worlds.

A goal of molecular materials chemistry is to develop synthetic strategies for the precise placement of molecular building blocks at nano-and mesoscale levels. If the building blocks comprise both organic and inorganic moieties, the resultant hybrid composites have the advantage of combining complementary strengths from two different chemical worlds. By piecing together a judicious choice of these components in a controlled manner, the complexity and functionality of the crystalline framework can be considerably enhanced 1. These materials, with properties that are difficult or impossible to achieve in a conventional solid lattice, may have far-reaching implications for a number of areas such as photovoltaics, magnetism and superconductivity. A classic example of these hybrid materials is intercalated compounds 2. Many layered materials, such as graphite and clay, occur naturally. When the space between the crystalline sheets is occupied by selected ions or molecules, intercalated crystalline solids with tunable electronic and optical properties are produced. For example, layered organic–inorganic perovskites have been successfully used for flexible, light-emitting devices as well as field-effect transistors 3,4. The inability to design and synthesize organic–inorganic hybrid materials in which the precise placement of molecular building blocks can be controlled, however, remains a problem. On page 68 of this issue, Samuel Stupp and co-workers take up this challenge and report a strategy for synthesizing well-ordered, alternating lamellar layers of electronically active, hybrid nanomaterials 5. One possible strategy towards functional optoelectronic composites is to use an organic material that can efficiently harness photons from light and convert them to useful energy through a highly conducting inorganic material 6. Until now, this has been achieved by incorporating structure-directing insulating organic materials to template-ordered nanoscale patterns of inorganic semiconductors, followed by removal of the organic component and infiltration with a functional organic material 7. This approach, however, does not further improve the nanoscale ordering nor does it take part in the crystallization process of self-assembly. The nanocomposites made by Stupp and colleagues 5 are composed of conjugated organic semiconductors and inorganic ZnO. The layers are deposited in one simple step directly onto the surface of an electrode, resulting in the fabrication of a photoconductor device. This remarkable hybrid system incorporates the spectral tunability of conjugated organic semiconductors and the highly conducting nature of ZnO to produce an air-stable photoconductor with unprecedented performance (Fig. 1). In general terms and in Stupp's hybrid system, the principle of operation of an organic–inorganic photoconductor is …