Here we show a step-wise approach for the formation of continuous shell-structures on surface-confined gold nanoparticles. The nanoparticle-cores induce order in the shell-structure, which consists of metal-organic networks. Communication between the organic and inorganic parts is reflected in their optical properties.

Stimuli responsive materials are capable of mimicking the operation characteristics of logic gates such as AND, OR, NOR, and even flip-flops. Since the development of molecular sensors and the introduction of the first AND gate in solution by de Silva in 1993, Molecular (Boolean) Logic and Computing (MBLC) has become increasingly popular. In this Account, we present recent research activities that focus on MBLC with electrochromic polymers and metal polypyridyl complexes on a solid support. Metal polypyridyl complexes act as useful sensors to a variety of analytes in solution (i.e., H(2)O, Fe(2+/3+), Cr(6+), NO(+)) and in the gas phase (NO(x) in air). This information transfer, whether the analyte is present, is based on the reversible redox chemistry of the metal complexes, which are stable up to 200 °C in air. The concurrent changes in the optical properties are nondestructive and fast. In such a setup, the input is directly related to the output and, therefore, can be represented by one-input logic gates. These input-output relationships are extendable for mimicking the diverse functions of essential molecular logic gates and circuits within a set of Boolean algebraic operations. Such a molecular approach towards Boolean logic has yielded a series of proof-of-concept devices: logic gates, multiplexers, half-adders, and flip-flop logic circuits. MBLC is a versatile and, potentially, a parallel approach to silicon circuits: assemblies of these molecular gates can perform a wide variety of logic tasks through reconfiguration of their inputs. Although these developments do not require a semiconductor blueprint, similar guidelines such as signal propagation, gate-to-gate communication, propagation delay, and combinatorial and sequential logic will play a critical role in allowing this field to mature. For instance, gate-to-gate communication by chemical wiring of the gates with metal ions as electron carriers results in the integration of stand-alone systems: the output of one gate is used as the input for another gate. Using the same setup, we were able to display both combinatorial and sequential logic. We have demonstrated MBLC by coupling electrochemical inputs with optical readout, which resulted in various logic architectures built on a redox-active, functionalized surface. Electrochemically operated sequential logic systems such as flip-flops, multivalued logic, and multistate memory could enhance computational power without increasing spatial requirements. Applying multivalued digits in data storage could exponentially increase memory capacity. Furthermore, we evaluate the pros and cons of MBLC and identify targets for future research in this Account.

Designer materials: HOMO–LUMO engineering of coordination-based oligomers covalently bound to silicon or glass has been achieved by the use of a partially fluorinated chromophore (see graphic). The experimental and computationally derived physical chemical properties of these assemblies are compared to their non-fluorinated analogues. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Assemblies with molecular-level organization based on organic chromophores and a bimetallic palladium complex are presented. A layer-by-layer strategy is employed by alternately coordinating vinylpyridine-terminated chromophores to the metal centers to form cationic oligomers. These new structures are formed from solution on quartz and silicon substrates functionalized with a covalently bound template layer. Twelve consecutive deposition steps result in structurally regular assemblies as demonstrated by linear increases in the ellipsometrically determined thickness and UV-vis optical absorption. The increase in thickness for each additional layer shows that the long-range order of the system is determined by the structure of the chromophores and by the square-planar geometry of the metal centers. Furthermore, the optical properties indicate that the conjugation length of the assembly component does not increase in the surface-bound oligomers with each additional deposition cycle. Structural communication is transferred via the system components, but they remain electronically isolated. This is supported by density functional theory (DFT) calculations.

Combining strong metal-ligand coordination and pi-pi interactions affords a 3D-ordered molecular-based multilayer. The organization of the assembly is apparent from the optical properties and X-ray reflectivity.

Optical detection of parts-per-million (ppm) levels of CO by a structurally well-defined monolayer consisting of bimetallic rhodium complexes on glass substrates has been demonstrated.

Accelerated growth of a molecular-based material that is an active participant in its continuing self-propagated assembly has been demonstrated. This nonlinear growth process involves diffusion of palladium into a network consisting of metal-based chromophores linked via palladium.

This contribution describes the reactivity of Pt(PEt3)(4) with (4-bromo-phenyl)-pyridin-4-yl-diazene. eta(2)-Coordination of Pt(PEt3)(2) to the NN moiety is kinetically preferable and followed by an aryl-halide bond activation process. This quantitative transformation proceeds under mild reaction conditions in solution and in the solid state. Mechanistic studies in solution indicate that the metal insertion into the aryl-halide bond is the rate-determining step. The reaction obeys first-order kinetics in the eta(2)-coordination complex with Delta G(298K) = 24.6 +/- 1.6 kcal/mol, Delta H = 26.5 +/- 1.6 kcal/mol, and Delta S = 6.6 +/- 5.0 eu. No effect on the reaction progress and NMR line shape has been observed in the presence of excess PEt3. However, competition experiments with the eta(2)-coordination complex and PhBr reveal that the product ratio can be altered by the presence of PEt3, indicating that the two aryl-halide bond activation processes proceed via different mechanistic pathways. Numerical analysis of a series of competition experiments fits a reaction scheme involving a unimolecular transformation from the eta(2)-coordination complex to the product of aryl-halide oxidative addition. This "ring-walking" process is kinetically accessible as shown by density functional theory (DFT) calculations at the PCM:PBE0/SDB-cc-pVDZ/PBE0/SDD level of theory.

Layer-by-layer assembly of two palladium coordination-based multilayers on silicon and glass substrates is presented. The new assemblies consist of rigid-rod chromophores connected by terminal pyridine moieties to palladium centers. Both colloidal palladium and PdCl2(PhCN)2 were used in order to determine the effect of the metal complex precursor on multilayer structure and optical properties. The multilayers were formed by an iterative wet-chemical deposition process at room temperature in air on a siloxane-based template layer. Twelve consecutive deposition steps have been demonstrated resulting in structurally regular assemblies with an equal amount of chromophore and palladium added in each molecular bilayer. The optical intensity characteristics of the metal-organic films are clearly a function of the palladium precursor employed. The colloid-based system has a UV-vis absorption maximum an order of magnitude stronger than that of the PdCl2-based multilayer. The absorption maximum of the PdCl2-based film exhibits a significant red shift of 23 nm with the addition of 12 layers. Remarkably, the structure and physiochemical properties of the submicron scale PdCl2-based structures are determined by the configuration of the approximately 15 angstroms thick template layer. The refractive index of the PdCl2-based film was determined by spectroscopic ellipsometry. Well-defined three-dimensional structures, with a dimension of 5 microm, were obtained using photopatterned template monolayers. The properties and microstructure of the films were studied by UV-vis spectroscopy, spectroscopic ellipsometry, atomic force microscopy (AFM), X-ray reflectivity (XRR), scanning electron microscopy (SEM), and aqueous contact angle measurements (CA).

Chemical addressing of the metal oxidation state of an osmium-based chromophore monolayer results in modulation of the optical properties in the entire visible region (400−750 nm). The monolayers are thermally robust, and 25 Os2+/Os3+ redox cycles are demonstrated.

Seeking economic solutions for the pre-treatment of polluted waters is at the forefront of current reverse osmosis (RO) desalination research. The modern trend is to remove the polluting species by various UF/MF membrane pretreatment schemes. This paper describes progress in an ongoing project aiming to improve membrane pre-treatment processes by placing dynamic membranes in front of the UF/MF unit so as to relieve the load on the downstream processing. Dynamic membranes (DM), a class of membranes that has not yet found general industrial application, are formed in situ by colloid deposition on a porous support. They are an attractive method to relieve the load on the downstream pre-treatment membranes because, once fouled, they can be removed and reformed in place. This research has shown that DM formation conditions for organic foulant retention are not necessarily those suggested in the literature for other applications. The membranes tested were formed by dead end filtration of a hydrous zirconium oxide colloidal suspension on inexpensive nondashwoven flat sheet supports and post-treated by a poly(acrylic acid) solution. The quality of a DM membrane was characterized by measurements of permeate flux and retention of ovalbumin, used as a model contaminant. The properties of dynamic membranes are known to depend on a large number of variables. Results are described showing the effect of parameters found to exert a significant influence on membrane properties. They include the zirconium oxide colloid concentration, the tightness of the support fabric, the pH level of the colloidal suspension and the poly(acrylic acid) post-treatment. The best dynamic membrane achieved exhibited 85% ovalbumin retention at a concentration of 1000 ppm and over 95% retention at a concentration of 50 ppm. Permeation rates were in the range of UF fluxes (10–50 l/m2·h·bar). The work carried out to date has yielded encouraging results that are being currently extended.

Membranes capable of providing reverse osmosis or ultrafiltration separation properties can be conveniently formed by depositing upon a porous support a suitable colloidal suspension. Such membranes are called dynamic membranes or formed in place membranes. Interest in dynamic membranes stems from several potential advantages: wide choice of substrate materials, relatively simple removal of a severely fouled or impaired membrane, long service life of the porous support and the possibility to withstand high temperature and pressure by use of suitable inorganic substrates.Dynamic membranes technology was pioneered by the Oak Ridge National Laboratory in the early sixties. The main research interest was in RO applications, mainly desalination. The last review pager summarizing progress in dynamic membrane research and development was published by Thomas in 1977. Since then, considerable research information has accumulated and interest in dynamic membranes has widened to potential ultrafiltration applications. It is the purpose of this paper to review the considerable research information that has accumulated in the last twenty years.The first part of the review provides a general background on the earlier development of dynamic membranes. The second part reviews studies of dynamic membrane formation, effects of feed constituents and some pioneering industrial applications. The third part reviews modeling and theoretical efforts. Predictive models are yet to be developed.The limited industrial applications of dynamic membranes seem to be related to the large number of parameters influencing their flow and separation characteristics, insufficient work on developing compact and efficient porous support modules and the need to customize the formulation of a dynamic membrane for each specific application. The concluding part of this review provides recommendations on major research and development directions that could accelerate wider beneficial industrial utilization of dynamic membranes.