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A new class of light-responsive supramolecular amphiphilic block copolymers (BCs) based on the association through multiple H-bonding between 4-isobutyloxyazobenzene motifs and 2,6-diacylaminepyridine units is reported. Block copolymers containing 2,6-diacylaminopyridine side units, as hydrophobic block, and poly(ethylene glycol), as a hydrophilic segment, were functionalized with either a carboxylic acid azodendron, via double H-bonding, or a thymine azobenzene, via triple H-bonding. The structural and thermal characterization of these supramolecular azo-copolymers in bulk and solution is presented. The work emphasizes the self-assembly of these supramolecular polymers in water and the study of their UV-light responsive properties by UV-vis spectroscopy, dynamic light scattering (DLS), transmission electron microscopy (TEM), and synchrotron small-angle X-ray (SAXS). The present noncovalent postpolymerization functionalization strategy has provided stable self-assemblies in water with light responsive properties that can be used to load and trigger the delivery of small fluorescent molecules. [ABSTRACT FROM AUTHOR]

We report the synthesis and characterization of a new class of photoreactive conjugated polymers (Mn= 9300 g mol-1, Đ = 1.24; Mn= 9100 g mol-1, Đ = 1.23; Mn= 8800 g mol-1, Đ = 1.24) consisting of functionalized polythiophene-containing photoresponsive groups, i.e. a polythiophene containing 4-hydroxy-2,5-dimethylbenzophenone (DMBP) ("photoenol") and/or maleimide groups. We evidence the chemical versatility and platform character of the generated light reactive polythiophenes in a range of examples by creating variable polythiophene functional 2D and 3D structures and morphologies. Single-chain nanoparticles and polymeric networks are formed by cross-linking of DMBP and maleimide containing polythiophene via UV light irradiation by varying the polymer concentration. Maleimide-functionalized polythiophene is employed for spatially resolved functionalization of surfaces and the coating of preformed 3D polymeric microstructures via direct laser writing (DLW). The generated polythiophene functional materials are carefully characterized via size exclusion chromatography, dynamic light scattering, and time-of-flight secondary ion mass spectrometry as well as FT-IR spectroscopy techniques. [ABSTRACT FROM AUTHOR]

Herein we report the preparationand characterization of dendronizedsupramolecular polymers composed of a carboxy-terminated azodendron,dAZO, and two different vinylpyridine-containing polymers: poly(4-vinylpyridine)(P4VP) and polystyrene-b-poly(4-vinylpyridine)(PS-b-P4VP) block copolymer. P4VPcan selectively complex dAZO through hydrogen-bonding interactions,thus resulting in liquid crystalline materials. Additionally, thisstrategy is also applicable to the preparation of dendronized supramolecularblock copolymers (BCs). Lamellar, cylindrical, and spherical morphologiesare observed for the BC complexes depending on the dAZO to vinylpyridinerepeating unit ratio. Photoinduced orientation of the azobenzene moietiesis obtained in films of the H-bonded materialsboth P4VP andPS-b-P4VP based complexesbyusing 488 nm linearly polarized light and characterized through birefringenceand dichroism measurements. High and stable values of birefringenceare obtained for polymers with azobenzene content as low as 2.7 wt%, thus demonstrating the benefits of preorganization in photoactivedendritic moieties in side-chain H-bonded materials. [ABSTRACT FROM AUTHOR]

We report on the synthesis and characterizationof a series ofamphiphilic linear–dendritic block copolymers (LDBCs) as wellas their self-assembly in water. The LDBCs are composed of a 2000g/mol poly(ethylene glycol) (PEG) linear segment linked to the fourthgeneration of a 2,2-di(hydroxymethyl)propionic acid (bis-MPA)-baseddendron containing 4-isobutyloxyazobenzene units (AZO) and hydrocarbonchains (C18) randomly connected to the periphery of the dendron. TEMand cryo-TEM images show that all the LDBCs form stable vesicles inwater. The influence of AZO/C18 ratio in the photoresponse of theself-assemblies has been assessed as well as the encapsulation ofboth hydrophilic (Rhodamine B) and hydrophobic (Nile Red) fluorescentprobes and the use of light as an external stimulus to trigger therelease of the probes. The results show that by diluting the azobenzenecontent at the periphery of the dendron, the trans-to-cisphotoisomerization rate can be substantiallyaccelerated and the light-induced release activity can be tuned beingthe vesicles with a 50/50 AZO/C18 ratio the ones suffering the mostsignificant changes upon irradiation. [ABSTRACT FROM AUTHOR]

Graphene nanoribbons are one-dimensional stripes of graphene with width- and edge-structure-dependent electronic properties. They can be synthesized bottom-up in solution to obtain precise ribbon geometries. Here we investigate the optical properties of solution-synthesized 9-armchair graphene nanoribbons (9-aGNRs) that are stabilized as dispersions in organic solvents and further fractionated by liquid cascade centrifugation (LCC). Absorption and photoluminescence spectroscopy reveal two near-infrared absorption and emission peaks whose ratios depend on the LCC fraction. Low-temperature single-nanoribbon photoluminescence spectra suggest the presence of two different nanoribbon species. Based on density functional theory (DFT) and time-dependent DFT calculations, the lowest energy transition can be assigned to pristine 9-aGNRs, while 9-aGNRs with edge-defects, caused by incomplete graphitization, result in more blue-shifted transitions and higher Raman D/G-mode ratios. Hole doping of 9-aGNR dispersions with the electron acceptor F 4 TCNQ leads to concentration dependent bleaching and quenching of the main absorption and emission bands and the appearance of red-shifted, charge-induced absorption features but no additional emission peaks, thus indicating the formation of polarons instead of the predicted trions (charged excitons) in doped 9-aGNRs.

The careful mapping of photoinduced reversible-deactivation radical polymerizations (RDRP) is a prerequisite for their applications in soft matter materials design. Here, we probe the wavelength-dependent behavior of photochemically induced atom transfer radical polymerization (ATRP) using nanosecond pulsed-laser polymerization (PLP). The photochemical reactivities at identical photon fluxes of methyl acrylate in terms of conversion, number-average molecular weight, and dispersity of the resulting polymers are mapped against the absorption spectrum of the copper(II) catalyst in the range of 305-550 nm. We observe a red shift of the action spectrum relative to the absorption spectrum of the copper(II) catalyst. Both the number-average molecular weight and the dispersity show a wavelength dependence, while the molecular weight and conversion remain linearly correlated. The reported data allow the judicious selection of optimum wavelengths for photoATRP.

The light-responsive adaptation of polymer materials typically requires different wavelengths or additional heat to induce reversible covalent bond formation and dissociation. Here, we bypass the use of invasive triggers by introducing light-stabilized dynamic materials that can undergo a repeatable change in topology from a covalently cross-linked material into a liquid polymer formulation by switching one visible light source on-and-off without the need for any additional triggers. Specifically, we exploit the photo-Diels-Alder reaction of triazolinediones with naphthalenes as a dynamic covalent cross-linking platform that enables green light-induced network formation, while the cross-linked material collapses through spontaneous cycloreversion upon standing in the dark at ambient temperature. Importantly, the covalent cross-links remain stabilized for as long as visible light is present, thereby retaining the material's structural integrity. This enables their potential use in an array of light-directed applications whereby network properties such as stiffness can be tuned by the mildest trigger of all: darkness.

We pioneer the synthesis of fluorescent single chain nanoparticles (SCNPs) via UV-light induced folding based on tetrazole chemistry directly in pure water. Water-soluble photoreactive precursor polymers based on poly(acrylic acid) (PAA) bearing tetrazole, alkene and tetraethylene glycol monomethyl ether moieties, (PAA n (Tet/p-Mal/TEG)), or simply tetrazoles moieties, PAA n (Tet), were generated via RAFT polymerization. While tetrazole, ene, and acrylic acid containing polymers fold via dual nitrile imine-mediated tetrazole-ene cycloaddition (NITEC) as well as nitrile imine-carboxylic acid ligation (NICAL), tetrazole and acrylic acid only functional prepolymers fold exclusively via NICAL. A detailed study of the underpinning photochemistry of NITEC and NICAL is also included. The resulting water-soluble SCNPs were carefully characterized via analytical techniques such as NMR, UV-vis, and fluorescence spectroscopy, as well as SEC and DLS.

Fourteen different "hairy-rod" conjugated polymers, 9,9-dioctylfluorene derivatives entailing 1,2,3-triazole, azomethine, ethynyle, biphenyle, stilbene, and azobenzene lateral units, are synthesized via modular conjugation and are systematically investigated with respect to their ability to selectively disperse SWCNTs. Four polymers of the azomethine type, with unprecedented selectivity toward dispersing (8,7), (7,6), and (9,5) SWCNT species, have been identified. In particular, azomethine polymers, herein applied for the first time for SWCNT dispersion, have been evidenced to be very effective in the highly selective solubilization of SWCNTs. The experimentally observed selectivity results are unambiguously supported by molecular dynamics simulations that account for the geometrical properties and deformation energy landscape of the polymer. Specifically, the calculations accurately and with high precision predict the experimentally observed selectivity for the (7,6) and (9,5) conformations.