Novel, stimulus-responsive supramolecular structures in the form of fibers, gels, and spheres, derived from an azobenzene-containing benzenetricarboxamide derivative, are described. Self-assembly of tris(4-((E)-phenyldiazenyl)phenyl)benzene-1,3,5-tricarboxamide (Azo-1) in aqueous organic solvent systems results in solvent dependent generation of microfibers (aq DMSO), gels (aq DMF), and hollow spheres (aq THF). The results of a single crystal X-ray diffraction analysis of Azo-1 (crystallized from a mixture of DMSO and H2O) reveal that it possesses supramolecular columnar packing along the b axis. Data obtained from FTIR analysis and density functional theory (DFT) calculation suggest that multiple hydrogen bonding modes exist in the Azo-1 fibers. UV irradiation of the microfibers, formed in aq DMSO, causes complete melting while regeneration of new fibers occurs upon visible light irradiation. In addition to this photoinduced and reversible phase transition, the Azo-1 supramolecules display a reversible, fiber-to-sphere morphological transition upon exposure to pure DMSO or aq THF. The role played by amide hydrogen bonds in the morphological changes occurring in Azo-1 is demonstrated by the behavior of the analogous, ester-containing tris(4-((E)-phenyldiazenyl)phenyl)benzene-1,3,5-tricarboxylate (Azo-2) and by the hydrogen abstraction in the presence of fluoride anions.

A single photomechanical supramolecular nanowire actuator with an azobenzene-containing 1,3,5-tricarboxamide derivative is developed by employing a direct writing method. Single nanowires display photoinduced reversible bending and the bending behavior follows first-order kinetics associated with azobenzene photoisomerization. A wireless photomechanical nanowire tweezers that remotely manipulates a single micro-particle is also demonstrated.

Fabrication of 3D biological structures reveals dynamic response to external stimuli. A liquid-crystalline bridge extrusion technique is used to generate 3D structures allowing the capture of Rayleigh-like instabilities, facilitating customization of smooth, helical, or undulating periodic surface textures. By integrating intrinsic biochemical functionality and synthetic components into controlled structures, this strategy offers a new form of adaptable materials.

No abstract

An azobenzene-containing supramolecular polydiacetylene (PDA) crystal undergoes a photoinduced reversible blue-to-red phase transition accompanied by crystal tearing.

Tubular materials created by self-assembly of small organic molecules have gained great attention recently. Fabrication of tubular structures that have precise dimensions by using conventional self-assembly approaches is extremely challenging. Herein we describe fabrication of a free-standing tubular polydiacetylene (PDA) sensor based on the meniscusguided self-assembly and polymerization of diacetylene (DA) monomers. The free-standing single PDA tube can be utilized as an unprecedented microcapillary-based sensor system, which requires only a minimum amount (70−140 nL) of an analyte solution. We have observed 4 orders of magnitude more sensitive to analytes than is a conventional PDA sensor when a biotinfunctionalized PDA tube is exposed to streptavidin. The microcapillary-based analytical method developed in this study should find great utility not only for PDA sensors but also for other free-standing wire sensor systems.

Among the polymers, polyaniline (PANI) is a unique conjugated polymer in that it can be tailored for specific applications through a non-redox acid/base doping process. 1-3Unfortunately, Its poor solubility in most common organic solvents has limited the industrial application of PANI because of its high aromatic nature, strong inter-chain hydrogen bonding, and high charge delocalization. The patterning of conjugated polymers on various substrates was achieved by using a variety of techniques, such as the deposition by scanning electrochemical microscopy, 4 screen printing, 5 micromolding in capillaries (MIMIC), 6 inkjet printing, 7 photochemical patterning by photolithography, 8 and microcontact printing through self-assembly monolayer (SAM).9 Recently, we reported micro-scale conducting pattern using the organic soluble PANI substituted with acid-labile tertbutyloxycarbonyl (t-BOC) group on the glass substrate and reversible photochromism between spiropyran (SP) and fluorecein molecules by photolithography.10-14 If this lightregulated reversible uptake and release of protons to SP is combined with the t-BOC-PANI, then the colorimetric change could be controlled by additional stimuli. We report here for the first time the reversible colorimetric change on patterned film of t-BOC-PANI/SP by various stimuli such as photo, thermal, acid/base. Result and DisscussionTo develop for producing patterned images, we tested the possibility of generating micro-patterned images based on the photochromism of t-BOC-PANI/SP system containing triphenylsulfonium triflate (TPSOTf, 5 wt %) as a photo acid generator.The solution of SP and t-BOC-PANI (1:1 molar ratio) was spin-cast to form 1 µm thick films on a glass plate. The film of dark red color was exposed to UV light with 10 mW/cm 2 for 1 min through a photomask without PEB (post-exposure bake) process; noted that t-BOC group of PANI was not completely removed in this process because the deprotection of t-BOC group requires high thermal stress (> 150 o C). Upon additional UV irradiation for one more min, the ME form change into MEH by proton transfer derived from photo acid generator to make an optical microstructure patterning. Thus, the dark red color film before irradiation was changed into bright green color pattern derived from MEH form and t-BOC-PANI at UV irradiated portions as shown in Figure 1 ((a) and (b)). When the film is irradiated with visible right or thermal treatment (50 for 2 min), MEH form completely disappears to SP form switching back to the original color. In this result, this reversible colorimetric change (writing and erasing) is ascribed to sequential chemical reactions of the C-O bond cleavage and C-O bond reformation of SP without deprotecting pathway of t-BOC group of PANI. This localized photochromic process was confirmed by changes in the UV spectra. Figure 2 shows them before (black line of left) and after different doses of UV exposure. The unexposed film displays two absorption bands at 320 and 585 nm, characteristic of undoped EB form of PANI...

A photoresponsive azobenzene derivative having a triazine core moiety was prepared. Self-assembly of the triazine containing azobenzene derivative (Azo-TA) in aqueous dimethylsulfoxide and N,N-dimethylformamide afforded fibrous supramolecular polymers. Melting and regeneration of the supramolecular polymer were observed with alternative 365 nm UV and visible light irradiation by reversible cis-trans isomerization of azobenzene moieties.