Search results for "Photoresponsive"
showing 10 items of 13 documents
Azobenzene-based difunctional halogen-bond donor: Towards the engineering of photoresponsive co-crystals
2014
Halogen bonding is emerging as a powerful non-covalent interaction in the context of supramolecular photoresponsive materials design, particularly due to its high directionality. In order to obtain further insight into the solid-state features of halogen-bonded photoactive molecules, three halogen-bonded co-crystals containing an azobenzene-based difunctional halogen-bond donor molecule, (E)-bis(4-iodo-2,3,5,6-tetrafluorophenyl)diazene, C12F8I2N2, have been synthesized and structurally characterized by single-crystal X-ray diffraction. The crystal structure of the non-iodinated homologue (E)-bis(2,3,5,6-tetrafluorophenyl)diazene, C12H2F8N2, is also reported. It is demonstrated that the stud…
Supramolecular control of liquid crystals by doping with halogen-bonding dyes
2017
Introducing photochromic or polymeric dopants into nematic liquid crystals is a well-established method to create stimuli-responsive photonic materials with the ability to "control light with light". Herein, we demonstrate a new material design concept by showing that specific supramolecular interactions between the host liquid crystal and the guest dopants enhance the optical performance of the doped liquid crystals. By varying the type and strength of the dopant-host interaction, the phase-transition temperature, the order parameter of the guest molecules, and the diffraction signal in response to interference irradiation, can be accurately engineered. Our concept points out the potential…
Photoresponsive Halogen-Bonded Liquid Crystals: The Role of Aromatic Fluorine Substitution
2019
A new strategy for controlling the liquid crystalline and photophysical properties of supramolecular mesogens assembled via halogen bonding is reported. Changing the degree of fluorination at the halogen-bond donor of the supramolecular liquid crystal allows for the fine-tuning of the halogen bond strength and thereby provides control over the temperature range of the mesophase. At least three fluorine atoms have to be present to ensure efficient polarization of the halogen-bond donor and the formation of a mesophase. In addition, it was found that stilbazole acceptors are superior to their azopyridine counterparts in promoting stable liquid crystalline phases. The halogen-bond-driven supra…
Wavelength-Gated Adaptation of Hydrogel Properties via Photo-Dynamic Multivalency in Associative Star Polymers.
2020
Abstract Responsive materials, such as switchable hydrogels, have been largely engineered for maximum changes between two states. In contrast, adaptive systems target distinct functional plateaus between these maxima. Here, we demonstrate how the photostationary state (PSS) of an E/Z‐arylazopyrazole photoswitch can be tuned by the incident wavelength across a wide color spectrum, and how this behavior can be exploited to engineer the photo‐dynamic mechanical properties of hydrogels based on multivalent photoswitchable interactions. We show that these hydrogels adapt to the wavelength‐dependent PSS and the number of arylazopyrazole units by programmable relationships. Hence, our material des…
Localized Liquid Secretion from a Photopatterned Liquid-Crystal Polymer Skin
2020
Liquid-releasing artificial skins are made from films made of a smectic liquid-crystal polymer network (LCN) photopolymerized in the presence of a photoactive azobenzene chromophore and a liquid-crystal porogen. The nonreactive porogen phase separates during the polymerization process, and the polymer forms a spongy polymer network filled with liquid. The liquid is excreted from the film when exposed to UV light upon conversion of trans-azobenzene to its cis isomer. Here, localized liquid secretion at preset positions at the polymer film is described. The design principle is based on creating a hybrid molecular architecture with both smectic and nonordered isotropic alignments in a continuo…
A photoresponsive graphene oxide-C60 conjugate.
2014
An all-carbon donor-acceptor hybrid combining graphene oxide (GO) and C60 has been prepared. Laser flash photolysis measurements revealed the occurrence of photoinduced electron transfer from the GO electron donor to the C60 electron acceptor in the conjugate
Efficient light-induced phase transitions in halogen-bonded liquid crystals
2016
Here, we present a new family of light-responsive, fluorinated supramolecular liquid crystals (LCs) showing efficient and reversible light-induced LC-to-isotropic phase transitions. Our materials design is based on fluorinated azobenzenes, where the fluorination serves to strengthen the noncovalent interaction with bond-accepting stilbazole molecules, and increase the lifetime of the cis-form of the azobenzene units. The halogen-bonded LCs were characterized by means of X-ray diffraction, hot-stage polarized optical microscopy, and differential scanning calorimetry. Simultaneous analysis of light-induced changes in birefringence, absorption, and optical scattering allowed us to estimate tha…
Photochemical behavior in azobenzene having acidic groups. Preparation of magnetic photoresponsive gels
2011
[EN] The photochemistry of three azobenzenes representing contrasting photochemical behaviors is described in the present work. Thus, Methyl Orange (MO, 4-[[(4-dimethylamino)phenyl]-azo]benzenesulfonic acid sodium salt, hereinafter (1) and 4-hydroxyazobenzene-4'-sulfonic acid (2) undergo in water fast photochemical proton shift, with decays in the microsecond timescale. In contrast to the previous cases, azobenzene-4,4'-dicarboxylic acid (3) undergoes photoisomerization in water. This photochemical behavior allows the preparation of aqueous gels with Aerosil as gelating agent (5% weight) exhibiting high cyclability and photoreversible isomerization of the trans to cis (300 nm irradiation) a…
Surface-relief gratings in halogen-bonded polymer-azobenzene complexes A concentration-dependence study
2017
In recent years, supramolecular complexes comprising a poly(4-vinylpyridine) backbone and azobenzene-based halogen bond donors have emerged as a promising class of materials for the inscription of light-induced surface-relief gratings (SRGs). The studies up to date have focused on building supramolecular hierarchies, i.e., optimizing the polymer–azobenzene noncovalent interaction for efficient surface patterning. They have been conducted using systems with relatively low azobenzene content, and little is known about the concentration dependence of SRG formation in halogen-bonded polymer–azobenzene complexes. Herein, we bridge this gap, and study the concentration dependence of SRG formation…
Supramolecular hierarchy among halogen and hydrogen bond donors in light-induced surface patterning
2015
Halogen bonding, a noncovalent interaction possessing several unique features compared to the more familiar hydrogen bonding, is emerging as a powerful tool in functional materials design. Herein, we unambiguously show that one of these characteristic features, namely high directionality, renders halogen bonding the interaction of choice when developing azobenzene-containing supramolecular polymers for light-induced surface patterning. The study is conducted by using an extensive library of azobenzene molecules that differ only in terms of the bond-donor unit. We introduce a new tetrafluorophenol-containing azobenzene photoswitch capable of forming strong hydrogen bonds, and show that an io…