Network Polydiacetylene Films: Preparation, Patterning, and Sensor Applications

Conjugated organic polymers generally must include large substituents for stability, either contained within or appended to the polymer chain. In polydiacetylenes, the substituents fulfill another important role: During topochemical polymerization, they control the spacing between the diyne monomers to produce an ordered polymer. By using a co-crystal scaffolding, we have prepared poly(diiododiacetylene), or PIDA, a nearly unadorned carbon chain substituted with only single-atom iodine side groups. The monomer, diiodobutadiyne, forms co-crystals with bis(nitrile) oxalamides, aligned by hydrogen bonds between oxalamide groups and weak Lewis acid-base interactions between nitriles and iodoalkynes. In co-crystals with one oxalamide host, the diyne undergoes spontaneous topochemical polymerization to form PIDA. The structure of the dark blue crystals, which look copper-colored under reflected light, has been confirmed by single-crystal x-ray diffraction, ultraviolet-visible absorption spectroscopy, and scanning electron microscopy. Show more

Detection of receptor-ligand interactions is generally accomplished by indirect assays such as enzyme-linked immunosorbent assay. A direct colorimetric detection method based on a polydiacetylene bilayer assembled on glass microscope slides has been developed. The bilayer is composed of a self-assembled monolayer of octadecylsilane and a Langmuir-Blodgett monolayer of polydiacetylene. The polydiacetylene layer is functionalized with an analog of sialic acid, the receptor-specific ligand for the influenza virus hemagglutinin. The sialic acid ligand serves as a molecular recognition element and the conjugated polymer backbone signals binding at the surface by a chromatic transition. The color transition is readily visible to the naked eye as a blue to red color change and can be quantified by visible absorption spectroscopy. Direct colorimetric detection by polydiacetylene films offers new possibilities for diagnostic applications and screening for new drug candidates or binding ligands. Show more

Nature abounds with intricate composite architectures composed of hard and soft materials synergistically intertwined to provide both useful functionality and mechanical integrity. Recent synthetic efforts to mimic such natural designs have focused on nanocomposites, prepared mainly by slow procedures like monomer or polymer infiltration of inorganic nanostructures or sequential deposition. Here we report the self-assembly of conjugated polymer/silica nanocomposite films with hexagonal, cubic or lamellar mesoscopic order using polymerizable amphiphilic diacetylene molecules as both structure-directing agents and monomers. The self-assembly procedure is rapid and incorporates the organic monomers uniformly within a highly ordered, inorganic environment. Polymerization results in polydiacetylene/silica nanocomposites that are optically transparent and mechanically robust. Compared to ordered diacetylene-containing films prepared as Langmuir monolayers or by Langmuir-Blodgett deposition, the nanostructured inorganic host alters the diacetylene polymerization behaviour, and the resulting nanocomposite exhibits unusual chromatic changes in response to thermal, mechanical and chemical stimuli. The inorganic framework serves to protect, stabilize, and orient the polymer, and to mediate its function. The nanocomposite architecture also provides sufficient mechanical integrity to enable integration into devices and microsystems. Show more