Soluble reduced graphene oxide sheets grafted with polypyridylruthenium-derivatized polystyrene brushes as light harvesting antenna for photovoltaic applications

XPS Depth-Profiling Studies of Chlorophyll Binding to Poly(cysteine methacrylate) Scaffolds in Pigment-Polymer Antenna Complexes Using a Gas Cluster Ion Source

X-ray photoelectron spectroscopy (XPS) depth-profiling with an argon gas cluster ion source (GCIS) was used to characterize the spatial distribution of chlorophyll a (Chl) within a poly(cysteine methacrylate) (PCysMA) brush grown by surface-initiated atom-transfer radical polymerization (ATRP) from a planar surface. The organization of Chl is controlled by adjusting the brush grafting density and polymerization time. For dense brushes, the C, N, S elemental composition remains constant throughout the 36 nm brush layer until the underlying gold substrate is approached. However, for either reduced density brushes (mean thickness ∼20 nm) or mushrooms grown with reduced grafting densities (mean thickness 6-9 nm), elemental intensities decrease continuously throughout the brush layer, because photoelectrons are less strongly attenuated for such systems. For all brushes, the fraction of positively charged nitrogen atoms (N+/N0) decreases with increasing depth. Chl binding causes a marked reduction in N+/N0 within the brushes and produces a new feature at 398.1 eV in the N1s core-line spectrum assigned to tetrapyrrole ring nitrogen atoms coordinated to Zn2+. For all grafting densities, the N/S atomic ratio remains approximately constant as a function of brush depth, which indicates a uniform distribution of Chl throughout the brush layer. However, a larger fraction of repeat units bound to Chl is observed at lower grafting densities, reflecting a progressive reduction in steric congestion that enables more uniform distribution of the bulky Chl units throughout the brush layer. In summary, XPS depth-profiling using a GCIS is a powerful tool for characterization of these complex materials.

Facile fabrication of a controlled polymer brush-type functional nanoprobe for highly sensitive determination of alpha fetoprotein

As robust functional polymers, polymer brush-based hybrid nanomaterials have potential application in the highly sensitive determination of tumor markers (TMs). Currently, there are plentiful reports on the polymerization methods of functional polymer brushes. Low ppm ATRP (activators (re)generated by electron transfer for atom transfer radical polymerization (A(R)GET ATRP), initiators for continuous activator regeneration atom transfer radical polymerization (ICAR ATRP) and electrochemically mediated atom transfer radical polymerization (eATRP)) is a facile and robust methodology with the advantages of simplicity, eco-friendliness and wide applicability to prepare well-defined polymeric materials. In this work, a controlled polymer brush-type functional nanoprobe is successfully fabricated by functional AGET ATRP and used as a sandwich-type electrochemical immunosensor for precise detection of TMs (alpha-fetoprotein, AFP). Using graphene oxide (GO) as an excellent conductive matrix, a GO-based poly-heterozygosis pyridine nanomaterial (GO@PHPY) is obtained by surface-initiated AGET ATRP and photocatalytic modification. The nanoprobe is assembled using GO@PHPY and a detection antibody (Ab2) to detect AFP, in which Cu(ii) serves as a signal label to coordinate with the pyridyl group. Under optimized conditions, the electrochemical sensor exhibits a good detection effect on AFP, with a detection range of 0.1 pg mL^-1 to 100 ng mL^-1 and a low detection limit of 0.08 pg mL^-1. It is worth noting that the detection platform can be applied to the detection of real human serum samples. Thus, it is a desirable platform for AFP detection in clinical diagnosis and practical applications. Meanwhile, this work proves that designing and constructing functional polymer brushes is one of the most effective methods for developing new materials for analytical scientific applications.

Facile architecture of highly effective nanofibrous membrane adsorbent via electrospun followed by hydrothermal carbonization for potential application in dye removal from water

Rapid removal of toxic dye pollutants in water by conventional materials is ineffective and expensive that warrants the necessity for the architecture of hybrid nanofibrous membrane through layer by layer deposition using electrospinning method. In order to achieve this, here we demonstrated the electrospun fabrication of graphene/ferrocene intercalated polyacrylonitrile nanofibrous (GFPN) membrane through hydrothermal carbonization (HTC) method and studied its potential adsorption properties for the removal of environmental pollutants. An aqueous dispersion of graphene/ferrocene (1 mg/mL) stabilized by the polymeric backbone was prepared by the solvent homogenization method and electrospun to yield nanofibrous membrane and further characterized by several analytical and spectroscopic techniques. Raman and XPS investigations corroborated the intercalation of graphene/Fe decorated onto the nanofibrous network. Adsorption experiments found that the GFPN membrane achieved more than 90% removal of anionic Congo red (CR) dye within 30 min in the aqueous phase irrespective of the concentration and takes some additional time for attaining the equilibrium. The longevity and stability of the membrane was studied by conducting successive adsorption-desorption cycles for the regeneration of its adsorption properties. The de-coloration mechanism was comprehensively investigated through the mathematical approaches using the kinetic and intraparticle diffusion studies and confirmed with the experimental findings through IR and XPS spectroscopic techniques. In a nutshell, this work focuses on the fabrication of hybrid nanofibrous membrane and studied its adsorption properties through varying concentrations of dye (20 to 150 mg/L). Moreover, this work extensively explored the mechanism associated with the adsorption process and specifically emphasize the existence of combined phenomena during the process, i.e., anion-cation interactions, hydrogen bonding, and successive stages of intraparticle diffusion through the comparative elucidation of both theoretical and experimental approaches.

Polymer grafting on graphene layers by controlled radical polymerization

In situ controlled radical polymerization (CRP) is considered as an important approach to graft polymer brushes with controlled grafting density, functionality, and thickness on graphene layers. Polymers are tethered with chain end or through its backbone to the surface or edge of graphene layers with two in situ polymerization methods of "grafting from" and "grafting through" and also a method based on coupling reactions known as "grafting to". The "grafting from" method relies on the propagation of polymer chains from the surface- or edge-attached initiators. The "grafting through" method is based on incorporation of double bond-modified graphene layers into polymer chains through the propagation reaction. The "grafting to" technique involves attachment of pre-fabricated polymer chains to the graphene substrate. Here, physical and chemical attachment approaches are also considered in polymer-modification of graphene layers. Combination of CRP mechanisms of reversible activation, degenerative (exchange) chain transfer, atom transfer, and reversible chain transfer with various kinds of grafting reactions makes it possible to selectively functionalize graphene layers. The main aim of this review is assessment of the recent advances in the field of preparation of polymer-grafted graphene substrates with well-defined polymers of controlled molecular weight, thickness, and polydispersity index. Study of the opportunities and challenges for the future works in controlling of grafting density, site-selectivity in grafting, and various topologies of the brushes with potential applications in stimuli-responsive surfaces, polymer composites, Pickering emulsions, coating technologies, and sensors is also considered.

Practical use of polymer brushes in sustainable energy applications: interfacial nanoarchitectonics for high-efficiency devices

The discovery and development of novel approaches, materials and manufacturing processes in the field of energy are compelling increasing recognition as a major challenge for contemporary societies. The performance and lifetime of energy devices are critically dependent on nanoscale interfacial phenomena. From the viewpoint of materials design, the improvement of current technologies inevitably relies on gaining control over the complex interface between dissimilar materials. In this sense, interfacial nanoarchitectonics with polymer brushes has seen growing interest due to its potential to overcome many of the limitations of energy storage and conversion devices. Polymer brushes offer a broad variety of resources to manipulate interfacial properties and gain molecular control over the synergistic combination of materials. Many recent examples show that the rational integration of polymer brushes in hybrid nanoarchitectures greatly improves the performance of energy devices in terms of power density, lifetime and stability. Seen in this light, polymer brushes provide a new perspective from which to consider the development of hybrid materials and devices with improved functionalities. The aim of this review is therefore to focus on what polymer brush-based solutions can offer and to show how the practical use of surface-grafted polymer layers can improve the performance and efficiency of fuel cells, lithium-ion batteries, organic radical batteries, supercapacitors, photoelectrochemical cells and photovoltaic devices.

Polymer-based chromophore-catalyst assemblies for solar energy conversion

The synthesis of polymer-based assemblies for light harvesting has been motivated by the multi-chromophore antennas that play a role in natural photosynthesis for the potential use in solar conversion technologies. This review describes a general strategy for using polymer-based chromophore-catalyst assemblies for solar-driven water oxidation at a photoanode in a dye-sensitized photoelectrochemical cell (DSPEC). This report begins with a summary of the synthetic methods and fundamental photophysical studies of light harvesting polychormophores in solution which show these materials can transport excited state energy to an acceptor where charge-separation can occur. In addition, studies describing light harvesting polychromophores containing an anchoring moiety (ionic carboxylate) for covalent bounding to wide band gap mesoporous semiconductor surfaces are summarized to understand the photophysical mechanisms of directional energy flow at the interface. Finally, the performance of polychromophore/catalyst assembly-based photoanodes capable of light-driven water splitting to oxygen and hydrogen in a DSPEC are summarized.

Probing photoinduced electron-transfer in graphene-dye hybrid materials for DSSC

We investigated the photophysical properties of a newly synthesized hybrid material composed of a triphenylamine dye covalently bound to reduced graphene oxide, potentially relevant as a stable photosensitizer in dye-sensitized solar cells. The photophysical characterization has been carried out by means of fluorescence quenching and fluorescence lifetime measurements, complemented by Electron Paramagnetic Resonance (EPR) spectroscopy, aimed at the detailed description of the photoinduced processes occurring in the hybrid and in the mixed hybrid/N-doped TiO₂ material. The combined optical/magnetic study unequivocally demonstrates a fast quenching of the dye excited state in the isolated hybrid and an efficient electron transfer to N-doped titania nanopowders. In the latter case, a metastable radical cation on the dye moiety is photogenerated and the corresponding negative charge, an electron, is trapped in defect sites of the doped semiconductor oxide. The spin distribution in the stable radical has been determined by EPR spectroscopy and correlated with DFT calculations.

Ruthenium based metallopolymer grafted reduced graphene oxide as a new hybrid solar light harvester in polymer solar cells

A new class of pyridyl benzimdazole based Ru complex decorated polyaniline assembly (PANI-Ru) was covalently grafted onto reduced graphene oxide sheets (rGO) via covalent functionalization approach. The covalent attachment of PANI-Ru with rGO was confirmed from XPS analysis and Raman spectroscopy. The chemical bonding between PANI-Ru and rGO induced the electron transfer from Ru complex to rGO via backbone of the conjugated PANI chain. The resultant hybrid metallopolymer assembly was successfully demonstrated as an electron donor in bulk heterojunction polymer solar cells (PSCs). A PSC device fabricated with rGO/PANI-Ru showed an utmost ~6 fold and 2 fold enhancement in open circuit potential (Voc) and short circuit current density (Jsc) with respect to the standard device made with PANI-Ru (i.e., without rGO) under the illumination of AM 1.5 G. The excellent electronic properties of rGO significantly improved the electron injection from PANI-Ru to PCBM and in turn the overall performance of the PSC device was enhanced. The ultrafast excited state charge separation and electron transfer role of rGO sheet in hybrid metallopolymer was confirmed from ultrafast spectroscopy measurements. This covalent modification of rGO with metallopolymer assembly may open a new strategy for the development of new hybrid nanomaterials for light harvesting applications.

Covalent Functionalization of Organic Nanoparticles Using Aryl Diazonium Chemistry and Their Solvent-Dependent Self-Assembly

A simple method for covalent functionalization of Fréchet-type dendron nanoparticles (FDNs) using tris-bipyridylruthenium(II) is described. Covalent functionalization is achieved by chemically reducing the diazo derivative of a ruthenium(II)bipyridine complex in the presence of FDNs wherein the radical species generated gets covalently linked to the nanoparticle surface. Simplicity, rapidity, and robustness are the advantages offered by the present approach. The nanoparticles, post functionalization, were characterized using transmission electron microscopy, thermogravimetric analysis, and infrared, energy-dispersive X-ray, UV-visible, and nuclear magnetic resonance spectroscopic techniques. Depending on the solvent, the ruthenium complex-linked FDN displays a range of morphologies, including nanoparticles, fiber-networks, and nanocapsules. In the nanocapsules and fiber-networks observed in organic solvents, the ruthenium complex is confined within the interior domain of the aggregate, whereas in the nanoparticles observed in water, it is present on the periphery. The formation of predictable morphologies in different solvents plays a key role in using such self-assembled structures for various applications such as sensing, catalysis, and light harvesting. Characterization of these nanoaggregates using different spectroscopic and microscopic techniques is also described.

Synthetic approaches towards structurally-defined electrochemically and (photo)redox-active polymer architectures

This review details synthetic strategies leading to structurally-defined electrochemically and (photo)redox-active polymer architectures,e.g.block, graft and end functionalized (co)polymers.

Protein-Framed Multi-Porphyrin Micelles for a Hybrid Natural-Artificial Light-Harvesting Nanosystem

A micelle-like hybrid natural-artificial light-harvesting nanosystem was prepared through protein-framed electrostatic self-assembly of phycocyanin and a four-armed porphyrin star polymer. The nanosystem has a special structure of pomegranate-like unimolecular micelle aggregate with one phycocyanin acceptor in the center and multiple porphyrin donors in the shell. It can inhibit donor self-quenching effectively and display efficient transfer of excitation energy (about 80.1 %) in water. Furthermore, the number of donors contributing to a single acceptor could reach as high as about 179 in this nanosystem.

Covalent functionalization of reduced graphene oxide with porphyrin by means of diazonium chemistry for nonlinear optical performance

Reduced graphene oxide (RGO)-porphyrin (TPP) nanohybrids (RGO-TPP 1 and RGO-TPP 2) were prepared by two synthetic routes that involve functionalization of the RGO using diazonium salts. The microscopic structures, morphology, photophysical properties and nonlinear optical performance of the resultant RGO-TPP nanohybrids were investigated. The covalent bonding of the porphyrin-functionalized-RGO nanohybrid materials was confirmed by Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, and thermogravimetric analysis. Attachment of the porphyrin units to the surface of the RGO by diazotization significantly improves the solubility and ease of processing of these RGO-based nanohybrid materials. Ultraviolet/visible absorption and steady-state fluorescence studies indicate considerable π-π interactions and effective photo-induced electron and/or energy transfer between the porphyrin moieties and the extended π-system of RGO. The nonlinear optical properties of RGO-TPP 1 and RGO-TPP 2 were investigated by open-aperture Z-scan measurements at 532 nm with both 4 ns and 21 ps laser pulses, the results showing that the chemical nanohybrids exhibit improved nonlinear optical properties compared to those of the benchmark material C₆₀, and the constituent RGO or porphyrins.

Ultrafast dynamics in multifunctional Ru(II)-loaded polymers for solar energy conversion

The use of sunlight to make chemical fuels (i.e., solar fuels) is an attractive approach in the quest to develop sustainable energy sources. Using nature as a guide, assemblies for artificial photosynthesis will need to perform multiple functions. They will need to be able to harvest light across a broad region of the solar spectrum, transport excited-state energy to charge-separation sites, and then transport and store redox equivalents for use in the catalytic reactions that produce chemical fuels. This multifunctional behavior will require the assimilation of multiple components into a single macromolecular system. A wide variety of different architectures including porphyrin arrays, peptides, dendrimers, and polymers have been explored, with each design posing unique challenges. Polymer assemblies are attractive due to their relative ease of production and facile synthetic modification. However, their disordered nature gives rise to stochastic dynamics not present in more ordered assemblies. The rational design of assemblies requires a detailed understanding of the energy and electron transfer events that follow light absorption, which can occur on time scales ranging from femtoseconds to hundreds of microseconds, necessitating the use of sophisticated techniques. We have used a combination of time-resolved absorption and emission spectroscopies with observation times that span 9 orders of magnitude to follow the excited-state evolution within polymer-based molecular assemblies. We complement experimental observations with molecular dynamics simulations to develop a microscopic view of these dynamics. This Account provides an overview of our work on polymers decorated with pendant Ru(II) chromophores, both in solution and on surfaces. We have examined site-to-site energy transport among the Ru(II) complexes, and in systems incorporating π-conjugated polymers, we have observed ultrafast formation of a long-lived charge-separated state. When attached to TiO2, these assemblies exhibit multifunctional behavior in which photon absorption is followed by energy transport to the surface and electron injection to produce an oxidized metal complex. The oxidizing equivalent is then transferred to the conjugated polymer, giving rise to a long-lived charge-separated state.

Recent advances in the synthesis and applications of graphene–polymer nanocomposites

We summarize the recent advances in the modification of graphene with polymers and the synthesis and applications of high quality graphene–polymer nanocomposites.

Theoretical oxidation state analysis of Ru-(bpy)3: influence of water solvation and Hubbard correction in first-principles calculations

Oxidation state is a powerful concept that is widely used in chemistry and materials physics, although the concept itself is arguably ill-defined quantum mechanically. In this work, we present impartial comparison of four, well-recognized theoretical approaches based on Lowdin atomic orbital projection, Bader decomposition, maximally localized Wannier function, and occupation matrix diagonalization, for assessing how well transition metal oxidation states can be characterized. Here, we study a representative molecular complex, tris(bipyridine)ruthenium. We also consider the influence of water solvation through first-principles molecular dynamics as well as the improved electronic structure description for strongly correlated d-electrons by including Hubbard correction in density functional theory calculations.