Photochromic organic-inorganic hybrid materials

Photochromic organic-inorganic hybrid materials have attracted considerable attention owing to their potential application in photoactive devices, such as optical memories, windows, photochromic decorations, optical switches, filters or non-linear optics materials. The growing interest in this field has largely expanded the use of photochromic materials for the purpose of improving existing materials and exploring new photochromic hybrid systems. This tutorial review summarizes the design and preparation of photochromic hybrid materials, and particularly those based on the incorporation of organic molecules in organic-inorganic matrices by the sol-gel method. This is the most commonly used method for the preparation of these materials as it allows vitreous hybrid materials to be obtained at low temperatures, and controls the interaction between the organic molecule and its embedding matrix, and hence allows tailoring of the performance of the resulting devices.     

How solvent controls electronic energy transfer and light harvesting

The way that solvent (or host medium) modifies the rate of electronic energy transfer (EET) has eluded researchers for decades. By applying quantum chemical methods that account for the way solvent (in general any host medium including liquid, solid, or protein, etc.) responds to the interaction between transition densities, we quantify the solvent screening. We find that it attains a striking exponential attenuation at separations less than about 20 A, thus interpolating between the limits of no apparent screening and a significant attenuation of the EET rate. That observation reveals a previously unidentified contribution to the distance dependence of the EET rate.     

Silica-based mesoporous organic-inorganic hybrid materials

Mesoporous organic-inorganic hybrid materials, a new class of materials characterized by large specific surface areas and pore sizes between 2 and 15 nm, have been obtained through the coupling of inorganic and organic components by template synthesis. The incorporation of functionalities can be achieved in three ways: by subsequent attachment of organic components onto a pure silica matrix (grafting), by simultaneous reaction of condensable inorganic silica species and silylated organic compounds (co-condensation, one-pot synthesis), and by the use of bissilylated organic precursors that lead to periodic mesoporous organosilicas (PMOs). This Review gives an overview of the preparation, properties, and potential applications of these materials in the areas of catalysis, sorption, chromatography, and the construction of systems for controlled release of active compounds, as well as molecular switches, with the main focus being on PMOs.     

Organogels as scaffolds for excitation energy transfer and light harvesting

The elegance and efficiency by which Nature harvests solar energy has been a source of inspiration for chemists to mimic such process with synthetic molecular and supramolecular systems. The insights gained over the years from these studies have contributed immensely to the development of advanced materials useful for organic based electronic and photonic devices. Energy transfer, being a key process in many of these devices, has been extensively studied in recent years. A major requirement for efficient energy transfer process is the proper arrangement of donors and acceptors in a few nanometers in length scale. A practical approach to this is the controlled self-assembly and gelation of chromophore based molecular systems. The present tutorial review describes the recent developments in the design of chromophore based organogels and their use as supramolecular scaffolds for excitation energy transfer studies.     

Cascade energy transfer in a conformationally mobile multichromophoric dendrimer

A conformationally flexible, generation-2,3 poly(aryl ether) dendrimer favors quantitative cascade fluorescence resonance energy transfer without the appearance of undesired chromophore self-quenching interactions such as excimer formation.     

Unprecedented laser action from energy transfer in multichromophoric BODIPY cassettes

A cassette molecule, featuring direct integration of two donor BODIPY units to one acceptor BODIPY unit, was conveniently developed as the first highly "through-bond energy transfer" (TBET) laser dye. This multicolor absorbing dye exhibited highly efficient and photostable laser action under drastic pumping conditions.     

Thermal degradation of epoxy-silica organic-inorganic hybrid materials

Degradation kinetics of organic-inorganic hybrid materials based on epoxy resin were investigated by thermogravimetric analysis (TGA). The hybrid materials were prepared from diglycidyl ether of bisphenol A (DGEBA) and 3-glycidyloxypropyltrimethoxysilane (GLYMO) polymerised simultaneously by poly(oxypropylene)diamine (Jeffamine D230). Nanometric level of homogeneity in the hybrids was verified by electron microscopy. Energy of activation of degradation for the hybrids with varying inorganic content, as well as for the unmodified epoxy-amine system, was determined by the isoconversional Kissinger-Akahira-Sunose method, and was found to be significantly higher for the hybrid materials than for the unmodified epoxy-amine system. The degradation process was described by empirical kinetic models. The results indicated that presence of the inorganic network influences the mechanism of degradation of organic phase. Greater thermal stability of hybrid materials was confirmed by other parameters obtained from TGA curves.     

The supramolecular chemistry of organic-inorganic hybrid materials

The combination of nanomaterials as solid supports and supramolecular concepts has led to the development of hybrid materials with improved functionalities. These "hetero-supramolecular" ideas provide a means of bridging the gap between molecular chemistry, materials sciences, and nanotechnology. In recent years, relevant examples have been reported on functional aspects, such as enhanced recognition and sensing by using molecules on preorganized surfaces, the reversible building of nanometer-sized networks and 3D architectures, as well as biomimetic and gated chemistry in hybrid nanomaterials for the development of advanced functional protocols in three-dimensional frameworks. This approach allows the fine-tuning of the properties of nanomaterials and offers new perspectives for the application of supramolecular concepts.     

Multichromophore light harvesting in hybrid solar cells

A new technologically relevant method for multichromophore sensitizing of hybrid blend solar cells is presented. Two dyes having complementary absorption in the UV-visible regions are individually adsorbed on nanocrystalline TiO(2) powder. These dyed TiO(2) nanoparticles are blended with an organic hole-conductor (HC) Spiro-OMeTAD in desired compositions and applied on a conducting substrate by doctor-blading at room temperature to fabricate multichromophore-sensitized hybrid blend solar cells. The external quantum efficiency (EQE) of the single hybrid layer system fabricated with two dyes, that absorb mainly UV (TPD dye) and visible regions (Ru-TPA-NCS dye), exhibited a clear panchromatic response with the sum of the EQE characteristics of each single dye cell. The first results of a multichromophore-sensitized solid-state solar cell showed J(sc) of 2.1 mA cm(-2), V(oc) of 645 mV, FF of 47% and efficiency of 0.65% at AM 1.5 G, 100 mW cm(-2) illumination intensity. The J(sc) of the multichromophore cell is the sum of the individually dyed solar cells. The process described here is technically very innovative and very simple in procedure. It has potentials to be adopted for panchromatic sensitization using more than two dyes in a single hybrid layer or layer-wise fabrication of a tandem structure at room temperature.     

Efficient light harvesting by sequential energy transfer across aggregates in polymers of finite conjugational segments with short aliphatic linkages.

Interactions between lumophores have a critical influence on the photophysical properties of conjugated polymers. We synthesized a new series of light-harvesting polymers (poly-DSBs, I-IV) of dialkyloxy- or dialkyl-substituted distyrylbenzene (the substituents being methoxy, 2-ethylhexyloxy, and cyclohexyl) with short aliphatic linkage (methylene or ethylene) and examined the effects of interactions between lumophores and of chemical structures on the absorption, emission, and excitation spectra. The proximity between distyrylbenzene lumophores was shown to be critical to the interactions between lumophores and to the energy-transfer processes. In concentrated solutions and solid films, intermolecular aggregates exist resulting from different extents of interactions between lumophores and are found to involve at least three species: loose, compact, and the most aligned aggregates as observed by photoluminescence and excitation spectroscopies. We also found, for the first time, sequential energy transfer from individual lumophores to the most compact, aligned aggregates via the looser intermolecular aggregates, as observed directly by time-resolved fluorescence spectroscopy. Such a process mimics energy transfer in photosynthesis units and is so efficient such that the fluorescence color can be red-shifted drastically by the presence of comparatively few aggregates and that the light evolved from concentrated solutions and films of poly-DSBs I-IV is entirely or almost the aggregation emission. Although the sequential energy-transfer process in fully conjugated electro-/photoluminescent polymers due to inhomogenity other than distributed conjugation lengths has never been directly observed at room temperature, we suggest that events similar to those observed in poly-DSBs in conjugated polymers could occur but on a much shorter time scale, i.e., a few picoseconds.     

Understanding and controlling organic-inorganic interfaces in mesostructured hybrid photovoltaic materials

The chemical compositions and structures of organic-inorganic interfaces in mesostructurally ordered conjugated polymer-titania nanocomposites are shown to have a predominant influence on their photovoltaic properties. Such interfaces can be controlled by using surfactant structure-directing agents (SDAs) with different architectures and molecular weights to promote contact between the highly hydrophobic electron-donating conjugated polymer species and hydrophilic electron-accepting titania frameworks. A combination of small-angle X-ray scattering (SAXS), scanning and transmission electron microscopy (SEM, TEM), and solid-state NMR spectroscopy yields insights on the compositions, structures, and distributions of inorganic and organic species within the materials over multiple length scales. Two-dimensional NMR analyses establish the molecular-level interactions between the different SDA blocks, the conjugated polymer, and the titania framework, which are correlated with steady-state and time-resolved photoluminescence measurements of the photoexcitation dynamics of the conjugated polymer and macroscopic photocurrent generation in photovoltaic devices. Molecular understanding of the compositions and chemical interactions at organic-inorganic interfaces are shown to enable the design, synthesis, and control of the photovoltaic properties of hybrid functional materials.     

Protein micropatterning on bifunctional organic-inorganic sol-gel hybrid materials

Active protein micropatterns and microarrays made by selective localization are popular candidates for medical diagnostics, such as biosensors, bioMEMS, and basic protein studies. In this paper, we present a simple fabrication process of thick (approximately 20 microm) protein micropatterning using capillary force lithography with bifunctional sol-gel hybrid materials. Because bifunctional sol-gel hybrid material can have both an amine function for linking with protein and a methacryl function for photocuring, proteins such as streptavidin can be immobilized directly on thick bifunctional sol-gel hybrid micropatterns. Another advantage of the bifunctional sol-gel hybrid materials is the high selective stability of the amine group on bifunctional sol-gel hybrid patterns. Because amine function is regularly contained in each siloxane oligomers, immobilizing sites for streptavidin are widely distributed on the surface of thick hybrid micropatterns. The micropatterning processes of active proteins using efficient bifunctional sol-gel hybrid materials will be useful for the development of future bioengineered systems because they can save several processing steps and reduce costs.     

Synthesis of polymeric organic-inorganic hybrid materials. Partially deacetylated chitin-silica hybrid

This work reports the synthesis of a novel polymeric organic-inorganic hybrid. The inorganic component is a silica network obtained by controlled hydrolysis of tetraethyl orthosilicate via sol-gel process and the organic counterpart is partially deacetylated chitin (CHI). The resulting polymer hybrids were homogeneous transparent film forming glassy materials being compatible through a wide composition range. Simultaneous thermal analysis of a CHI/silica 1:1 mixture confirms the intermolecular complex formation between organic and inorganic polymers.     

Molecular design of hybrid organic-inorganic materials with electronic properties

The synthesis of two classes of hybrid organic-inorganic nanocomposites with electronic properties is reported. One is made of PDMS units cross linked with vanadium oxo-species where the vanadium coordination depends on the hydrolysis pH. Tetrahedral coordination is retained at neutral pH, while acidic conditions promote the segregation of five coordinated vanadium oxo-species. The reduction process depends also on the vanadium coordination. The second system is made of siloxane T units and polypyrrole oligomers, grafted and interpenetrated at a nano size level.     

Study of cure kinetics of epoxy-silica organic-inorganic hybrid materials

Cure kinetics of organic-inorganic hybrids based on epoxy resin was investigated, using differential scanning calorimetry (DSC). Thermoset hybrid materials were prepared from diglycidyl ether of bisphenol A (DGEBA) as organic precursor, and 3-glycidyloxypropyltrimethoxysilane (GLYMO) as inorganic precursor. Precursors were polymerised simultaneously using poly(oxypropylene)diamine (Jeffamine D230) as a curing agent. Isothermal DSC characterisation of DGEBA/Jeffamine system and two hybrid DGEBA/GLYMO/Jeffamine systems, with DGEBA and GLYMO mixed in mass ratios of 2:1 and 1:1, respectively, was performed at different temperatures. Applicability of empirical models, commonly used to describe the curing kinetics of thermosets, to hybrid systems was investigated, and the resulting parameters were tested on dynamic DSC scans. Additionally, prepared materials were studied by FTIR and the extraction in tetrahydrofuran. The presence of inorganic phase was found to hinder complete cross-linking of organic phase and influence the kinetics of cure.     

Auto-organisation of hybrid organic-inorganic materials prepared by sol-gel process

Silica-based hybrid organic-inorganic materials prepared by sol-gel chemistry exhibit chemical and physical properties revealing their anisotropic organisation. Besides the opportunities that this phenomenon opens for the preparation of new materials, it also provides arguments to the chemist looking for a better comprehension and control of the organisation of solids.     

Tetraalkylphosphonium polyoxometalate ionic liquids: novel, organic-inorganic hybrid materials

Pairing of a Keggin or Lindqvist polyoxometalate (POM) anion with an appropriate tetraalkylphosphonium cation is shown to yield the first members of a new family of ionic liquids (ILs). Detailed characterization of one of them, an ambient-temperature "liquid POM" comprising the Lindqvist salt of the trihexyl(tetradecyl) phosphonium cation, by voltammetry, viscometry, conductimetry, and thermal analysis indicates that it exhibits conductivity and viscosity comparable to those of the one previously described inorganic-organic POM-IL hybrid but with substantially improved thermal stability.     

Novel carbon materials for thermal energy harvesting

To decrease the consumption of fossil fuels, research has been done on utilizing low grade heat, sourced from industrial waste streams. One promising thermoenergy conversion system is a thermogalvanic cell; it consists of two identical electrodes held at different temperatures that are placed in contact with a redox-based electrolyte [1, 2]. The temperature dependence of the direction of redox reactions allows power to be extracted from the cell [3, 4]. This study aims to increase the power conversion efficiency and reduce the cost of thermogalvanic cells by optimizing the electrolyte and utilizing a carbon based electromaterial, reduced graphene oxide, as electrodes. Thermal conductivity measurements of the K₃Fe(CN)₆/K₄Fe(CN)₆ solutions used, indicate that the thermal conductivity decreases from 0.591 to 0.547?W/m?K as the concentration is increased from 0.1 to 0.4?M. The lower thermal conductivity allowed a larger temperature gradient to be maintained in the cell. Increasing the electrolyte concentration also resulted in higher power densities, brought about by a decrease in the ohmic overpotential of the cell, which allowed higher values of short circuit current to be generated. The concentration of 0.4?M K₃Fe(CN)₆/K₄Fe(CN)₆ is optimal for thermal harvesting applications using R-GO electrodes due to the synergistic effect of the reduction in thermal flux across the cell and the enhancement of power output, on the overall power conversion efficiency. The maximum mass power density obtained using R-GO electrodes was 25.51?W/kg (three orders of magnitude higher than platinum) at a temperature difference of 60?°C and a K₃Fe(CN)₆/K₄Fe(CN)₆ concentration of 0.4?M.