Biological matrices can direct the absolute alignment of inorganic crystals such as calcite. Cooperative effects at an organic-inorganic interface resulted in similar co-alignment of calcite at polymeric Langmuir-Schaefer films of 10,12-pentacosadiynoic acid (p-PDA). The films nucleated calcite at the (012) face, and the crystals were co-aligned with respect to the polymer's conjugated backbone. At the same time, the p-PDA alkyl side chains reorganized to optimize the stereochemical fit to the calcite structure, as visualized by changes in the optical spectrum of the polymer. These results indicate the kinds of interactions that may occur in biological systems where large arrays of crystals are co-aligned.

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Polymerized thin films based on polydiacetylenes (PDAs) undergo distinct color transitions that lend themselves to applications in biosensing, surface modification, nonlinear optics, and molecular electronics. The mechanism of the thermochromic blue to red color transition of PDA thin films was investigated at the molecular level using atomic force microscopy and at the macroscopic level with visible absorption and Fourier transform infrared spectroscopy. The thermochromic transition temperature is found to be between 70 and 90°C. At the molecular level, the ordering of the film increases at the thermochromic transition and remains ordered up to temperatures well above the transition (e.g., 130°C). No evidence for previously suggested entanglement or disordering of the alkyl side chains is observed. The pendant side chains rearrange from a partially disordered configuration characteristic of the blue film, to a well-ordered closepacked hexagonal arrangement in the red form. The rearrangment of the pendant side chains is linked to the formation of the red phase PDA.

Polydiacetylenic lipid membranes offer a general 'litmus test' for molecular recognition at the surface of a membrane. A concentration of 20 ppm of protein could be detected using polymerized thin films. The speed, sensitivity and simplicity of the design offers a new and general approach towards the direct colorimetric detection of a variety of different molecules.