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.

https://science.sciencemag.org/content/sci/261/5121/585.full.pdf

Direct colorimetric detection of a receptor-ligand interaction by a polymerized bilayer assembly

Organic microcrystals ranging from several tens nm to µm in size of several chromophores were successfully prepared by simply dispersing ethanol solutions of compounds into stirred water, i.e. by a reprecipitation method. The size of microcrystals was found to depend on concentration of ethanol solutions, dispersing conditions, temperature and so on.

https://iopscience.iop.org/article/10.1143/JJAP.31.L1132/pdf

A Novel Preparation Method of Organic Microcrystals

In this Review, the extreme care that must be taken when predicting the optical properties of conjugated polymers via the oligomer approach, and when comparing theoretical and experimental data, is illustrated. In the first part, conceptual strategies for the correct determination of optical transitions from experimental spectra and relevant extrapolation procedures at the polymer limit are introduced. The impact of conformational, substitution, solvent, and solid-state effects on the optical properties is discussed in light of experimental data reported for molecular backbones based on phenylene, phenylenevinylene, and thiophene repeat units. A comparison is then made between experimental results and those provided by standard quantum-chemical methods, to assess their reliability.

Optical Bandgaps of π‐Conjugated Organic Materials at the Polymer Limit: Experiment and Theory

Color and Chromism of Polydiacetylene Vesicles

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.

Self-assembly of mesoscopically ordered chromatic polydiacetylene/silica nanocomposites

Solutions of certain urethane substituted polydiacetylenes undergo dramatic, reversible color changes on addition of a nonsolvent. In some cases, the lowest energy optical transition of the polymer shifts by more than 5000 cm−1 (21 300 cm−1 to 15 900 cm−1 when the nonsolvent is added). The color changes are shown to be due to a planar–nonplanar conformational transition of the polymer backbone. The planar, fully‐conjugated conformation is stabilized by intramolecular hydrogen bonding between urethane functionalities on adjacent substituent groups.

A planar–nonplanar conformational transition in conjugated polymer solutions

The optical properties of single crystals and solution‐cast films of two polydiacetylenes, poly3BCMU and poly4BCMU where the substituent group is– (CH2)3.4OCONHCH4COOC4H9, are characterized. Visible absorption and reflection spectra for the polymer crystals are typical of those observed for other urethane substituted polydiacetylenes. The optical properties of the polymer films are controlled primarily by intramolecular hydrogen bonding between the N–H and C=O of the urethane functionalities on adjacent substituent groups. Hydrogen bonding stabilizes the planar, fully conjugated conformation of the individual polymer chains in the films. Increased temperature causes a disruption of the hydrogen bond network and a destabilization of the planar polymer conformation. Dramatic color changes result because of the sensitivity of the optical properties to backbone conformation.

Thermal effects on the optical properties of single crystals and solution‐cast films of urethane substituted polydiacetylenes

A visual conformational transition in a polymer solution

Results are presented for the thermal, ultraviolet, and γ-ray polymerization of 2,4-hexadiyne-1,6-diol bis-(p-toluene sulfonate) (PTS). Monomer extraction is used to obtain polymer conversion-vs.-time curves at 30, 50, and 80°C. In agreement with previous work over a narrower temperature range, the curves all display a dramatic autocatalytic effect with an onset at about 10% conversion to polymer. Although the polymerization rate undergoes a 200-fold change over this temperature range, the shape of the conversion curves does not change. These data yield an activation energy (E) of 22.2 ± 0.4 kcal/mole when interpreted in terms of the time required to reach 50% polymer. An annealing technique is used to provide a closer look at the autocatalytic region. In that case, E = 22.5 ± 0.8 kcal/mole is determined from measurements of the time required to go from 10 to 50% polymer at temperatures ranging from 23 to 80°C (a 500-fold change in rate). Thermal polymerization rates measured in the low-conversion limit using a spectroscopic method based on diffuse reflectance yield E = 22.8 ± 0.6 kcal/mole. Thus E is independent of polymer conversion and the autocatalytic effect can be best understood as arising from a large increase in the propagation length of the polymer chains. The autocatalytic effect is shown to be present in both UV and γ-ray polymerization. In the case of γ-ray polymerization, conversion-vs.-time and spectroscopic measurements are consistent with inhomogeneities in the polymer concentration caused by particle tracks. Activation energies for UV and γ-ray polymerization are quite low (2-3 kcal/mole) and confirm that the chain initiation event makes the major energetic contribution to E. The polymerization mechanism is discussed in detail. The photopolymerization experiments can be consistently interpreted with a model based on the triplet excited state of the diacetylene monomer as the chain initiation species.

Solid‐state polymerization of a diacetylene crystal: Thermal, ultraviolet, and γ‐ray polymerization of 2,4‐hexadiyne‐1,6‐diol bis‐(p‐toluene sulfonate)

G. N. Patel

Papers

A planar–nonplanar conformational transition in conjugated polymer solutions

Thermal effects on the optical properties of single crystals and solution‐cast films of urethane substituted polydiacetylenes

A visual conformational transition in a polymer solution

Solid‐state polymerization of a diacetylene crystal: Thermal, ultraviolet, and γ‐ray polymerization of 2,4‐hexadiyne‐1,6‐diol bis‐(p‐toluene sulfonate)