Colloidally Stable Monolayer Nanosheets with Colorimetric Responses

Despite the discovery of chromogenic‐layered materials for decades of years, fabrication of colloidally stable monolayer organic 2D nanosheets in aqueous media with colorimetric responses is still challenging. Herein reported is the first solution synthesis of chromic monolayer nanosheets via the topochemical polymerization of self‐assembled amphiphilic diacetylenes in aqueous media. The polydiacetylene (PDA) nanosheets are ≈3–4 nm thick in solution and only ≈1.9 nm thick in the dried state, while the lateral size can reach several micrometers. Moreover, the aqueous stability endows PDA nanosheets with excellent processability, which can further assemble into films via vacuum filtration or act as an ink for high‐resolution inkjet printing. The filtrated films and printed patterns exhibit fully reversible blue‐to‐red thermochromism, and the film also displays an interesting reversible colorimetric transition in response to near‐infrared light, which is not reported for other PDA‐only systems. The present colloidal PDA nanosheets should represent a new kind of chromic organic 2D nanomaterials that may be applied as novel building blocks for developing intelligent hybrid materials and may also find diverse sensing, display and/or anticounterfeiting applications.     

Covalently Linked Perylene Diimide–Polydiacetylene Nanofibers Display Enhanced Stability and Photocurrent with Reversible FRET Phenomenon

Because of their unique structural and optical properties, 1D perylene diimide (PDI) derivatives have gained attention for use in optoelectronic devices. However, PDI‐containing self‐assembled supramolecular systems often are of limited use because they have supramolecular architectures that are held together by weak noncovalent π–π stacking, hydrogen bonding, and hydrophobic interactions. As a result, they are intrinsically unstable under solution‐processing conditions. To overcome this limitation, a polydiacetylene (PDA)‐based strategy is developed to construct a solvent‐resistant and stable PDI assembly. For this purpose, first the monomer PDI–BisDA is generated, in which two polymerizable diacetylene (DA) units are covalently linked to a PDI core. Importantly, 254 nm UV irradiation of self‐assembled PDI–BisDA nanofibers forms solvent‐resistant and stable PDI–PDA fibers. Owing to the presence of PDA, the generated polymer fibers display an increased photocurrent. In addition, the existence of PDA and PDI moieties in the fiber leads to the occurrence of switchable on–off fluorescence resonance energy transfer (FRET) between the PDI and reversibly thermochromic PDA chromophores.     

Growth, polymerization and oxidation characteristics of PA-PDA single crystals

The growth, polymerization and oxidation characteristics of PA-PDA (polyacetylene-polydiacetylene) crystals are described. Simultaneous crystallization and polymerization of (HCC(CH₂)₈---CC---)₂ from a solution in 1,11-dodecadiyne was found to be the best means for obtaining fully polymerized PA-PDA crystals. The electrical conductivity of PA-PDA decreased by approximately two orders of magnitude upon exposure to air over the period of a year. The oxidation characteristics of the polyacetylene chain in PA-PDA were essentially similar to that of trans-polyacetylene by itself. However, oxygen probably remained as a dopant in these crystals for a long time before chemically bonding to the backbones.     

Electric field depolarization in high aperture focusing with emphasis on annular apertures

Electromagnetic focusing theory of light predicts that at high apertures field components arise that are polarized perpendicular to the initial polarization. Although vectorial depolarization has received considerable attention in focusing theory, no evidence has been presented as to its relevance in experiments. We measure the intensity of the perpendicularly orientated field in the focal region by utilizing monomolecular, fluorescent polydiacetylene layers whose transition dipoles are orientated in a single direction. For a 1.4 numerical aperture oil objective lens illuminated with linearly x -polarized light, we find that the integral of the modulus squared of the y -polarized focal field amounts to 1.5% of its x -polarized counterpart. In particular, we show here that the depolarization increases when using annular apertures. Annuli formed by a central obstruction with a diameter of 89% of that of the entrance pupil raise the integral to 5.5%. This compares well with the value of 5.8% predicted by electromagnetic focusing theory; however, the depolarization is also due to imperfections connected with focusing by refraction. Besides fluorescence microscopy and single molecule spectroscopy, the measured intensity of the depolarized component in the focal plane is relevant to all forms of light spectroscopy combining strong focusing with polarization analysis.     

Temperature-Controlled Pathway Complexity in Self-Assembly of Perylene Diimide-Polydiacetylene Supramolecule

Self-assembly process represents one of the most powerful and efficient methods for designing functional nanomaterials. For generating optimal functional materials, understanding the pathway complexity during self-assembly is essential, which involves the aggregation of molecules into thermodynamically or kinetically favored pathways. Herein, a functional perylene diimide (PDI) derivative by introducing diacetylene (DA) chains (PDI-DA) is designed. Temperature control pathway complexity with the evolution of distinct morphology for the kinetic and thermodynamic product of PDI-DA is investigated in detail. A facile strategy of UV-induced polymerization is adopted to trap and capture metastable kinetic intermediates to understand the self-assembly mechanism. PDI-DA showed two kinetic intermediates having the morphology of nanosheets and nanoparticles before transforming into the thermodynamic product having fibrous morphology. Spectroscopic studies revealed the existence of distinct H- and J-aggregates for kinetic and thermodynamic products respectively. The polymerized fibrous PDI-DA displayed reversible switching between J-aggregate and H-aggregate.