Here we nanoengineered tunable quantum dot and cationic conjugated polymer nanoarrays based on surface plasmon
enhanced fluorescence where we achieved a 15-fold and 25-fold increase in their emission intensities, respectively.
These peptide mediated hybrid systems were fabricated by horizontally tuning the localized surface plasmon resonance
of gold nanoarrays and laterally tuning the distance of the fluorophore from the metal surface. This approach permits a
comprehensive control both laterally (i.e., lithographically defined gold nanoarrays) and vertically (i.e., QD/CCP-metal
distance) of the collectively behaving QD-NP and CP-NP assemblies by way of biomolecular recognition. The highest
photoluminescence was achieved when the quantum dots and cationic conjugated polymers were self-assembled at a
distance of 16.00 nm and 18.50 nm from the metal surface, respectively. Specifically, we demonstrated the spectral
tuning of plasmon resonant metal nanoarrays and the self-assembly of protein-functionalized QDs/CCPs in a step-wise
fashion with a concomitant incremental increase in separation from the metal surface through biotin-streptavidin spacer
units. These well-controlled self-assembled patterned arrays provide highly organized architectures for improving optoelectronic
devices and/or increasing the sensitivity of bio-chemical sensors.
Future generations of flexible, transparent electronics will require the use of polymer based thin-film transistors (TFTs) exhibiting high carrier mobility. The problem of enhancing TFT characteristics is addressed in this report. We investigate the nanoscale, self-assembled monolayer (SAM) influence on organic-based thin film transistors (OTFT) at the interface between semiconducting polymer and both the source/drain metal contacts and the insulator. Capacitance-voltage (C-V) characteristics help to elucidate the role of SAMs in the OTFT structure and the charge injection mechanism. Positive trends and parasitic effects are also addressed in characterization.
Self-assembly, the spontaneous organization of parts into ordered arrays and structures, is an omnipresent process in nature. Our group explores the use of self-assembly as an engineering concept to construct functional devices across the size scale. In this paper we present two examples of self-assembly. In the first example, we show how self-assembled monolayers of anthryl phosphonic acid can be used to form a nano-scale charge conduction channel. The molecular monolayer forms on a silicon dioxide surface and is placed between two metal electrodes. We have synthesized the molecules, verified the formation of the monolayer with X-ray photoemission spectroscopy and atomic force microscopy, and characterized the lateral charge carrier transport properties of the molecules. This molecular monolayer provides a facile way for integration of a nano-scale electronic device with conventional circuitry. In the second example, we demonstrate how microfabricated components can self-assemble into an electrical network. We have developed a microfabrication process for parallel production of 100 mm hexagonal silicon parts each carrying a portion of an electrical network. We functionalize the parts either with a low-melting point alloy or with a polymer and allow for their self-assembly into an ordered lattice at an air-water interface due to capillary forces.
Recent progress in developing high-performance organic polymers for electro-optics and photonics is reviewed. A highly fluorinated hyperbranched aromatic polymer with the degree of branching around 0.51 was prepared by a mild one-step polyesterification of an AB2 type monomer. Further post-functionalization with and thermally cross-linking by aromatic trifluorovinyl ethers (TFVE) afforded thermally stable, low loss optical polymer with improved solvent resistance. By more precisely controlling the molecular nano-architecture, we have developed a series of highly fluorinated crosslinkable dendrimers. These materials possess most of the desirable properties needed for the fabrication of optical waveguides, such as high solubility in common organic solvents (up to 50 wt%), very low optical loss, and excellent thermal stability. To overcome the “nonlinearity-stability tradeoff,” a facile and reversibly crosslinkable NLO polymer system is developed that combines both advantages of high poling efficiency and good alignment thermal stability. By smartly controlling the poling and crosslinking processes through the reversible Diels-Alder (DA) reactions, it allows highly polarizable chromophores to be efficiently poled at the stage of low viscosity linear thermoplastic polymer. The resulting nonlinear optical polymer exhibits a combination of a very large r33 value (76 pm/V at 1.3 μm) and good temporal stability at 70°C.
Recent progress in developing high-performance nonlinear optical chromophores and polymers for electro-optics is reviewed. Using the single-mode focused microwave irradiation, a diversified family of 2,5-dihydrofuran derivatives has been synthesized as a new class of tunable electron acceptors. Very large r33 values (128 and 116 pm/V at 1.3 μm) have been demonstrated by doping one of the 2-dicyanomethylen-3-cyano-4,5,-dimethyl-5-trifluoromethyl-2,5-dihydrofuran (CF3-TCF)-based chromophores in poly(methyl methacrylate) (PMMA) and a high Tg polyquinoline (PQ-100), respectively. An excellent long-term temporal stability at 85°C has also been maintained in the PQ system. Two side-chain dendronized NLO polymers have been synthesized. Using a mild, simple, and generally applicable post-functionalization method, highly polarizable chromophores with dendritic modification has been covalently attached to side chains of poly(4-hydroxystryene). This approach provides the combined advantages of achieving better poling efficiency through the dendritic effect and shortening the development time required for E-O dendrimer synthesis. Systematic property comparison between these polymers and other conventional NLO polymers, such as guest-host and simple side-chain polymers, has been performed. Exceptionally high poling efficiency (a very large E-O coefficient of 97 pm/V at 1.3 μm) and good temporal stability at room temperature were dmeonstrated in this dendronized side-chain polymer system.
Recent development of dendron-containing NLO chromophores and polymers is summarized. By modifying the chromophore shape or applying the site isolation principle to these materials, we have systematically build up our understanding of how to molecular engineer the NLO materials. In this process, we have introduced the dentritic structures to these materials, varied from 3-D shaped dendritic chromophore, to fully-functionalized dendrimers with the center cores of NLO chromophores and crosslinkable periphery, and to side-chain dendronized NLO polymers. Compared to the conventional designed organic NLO materials, these nanoscale tailored NLO chromophores and macromolecules provide great opportunities for the simultaneous optimization of macroscopic electro-optic activity, thermal stability, and optical loss.
Monte Carlo simulations suggest that the functionalization of bulky side groups on highly efficient nonlinear optical chromophores will improve the poling efficiency of the electro-optic polymers by reducing the intermolecular electrostatic interactions from these large dipole moments (μ) chromophores. However, very little information has been provided from theoretical simulation to describe the optimal functionality of the bulky side group needed on individual chromophore in order to be compatible with its environment, e.g. neighboring chromophores and polymer matrix. To further understand the influence of side-chain modification of chromophore on both chromophore-chromophore and chromophore-polymer matrix interactions, we have synthesized a series of highly polarizable nonlinear optical chromophores with various side-chain modifications in terms of shape, rigidity and functionality. Linear E-O coefficients (r33) of these functionalized chromophores in amorphous poly(carbonate) were evaluated using the contact poling technique. Several important chromophore and polymer parameters, such as, steric hindrance and free volume were used to explain the overall results from chromophore-chromophore and chromophore-polymer matrix interactions on E-O property.
A wide variety of aromatic trifluorovinyl ether monomers and highly fluorinated crosslinkable dendrimers have been developed via novel synthetic strategies. Through the thermal dimerization of trifluorovinyl ether moieties on the monomers or on the periphery of dendrimers, these monomers or dendrimers can be melt or solution polymerized to form perfluorocyclobutane(PFCB)-containing prepolymers with good processability for optical waveguide fabrication. By further thermal crosslinking, the resulting thermoset materials possess low optical loss (0.3-0.4 dB/cm at 1310 nm with 1% of DR-1 or DCM doping), high thermal stability (Tg: 100-400 °C), good thermo-optic property, high solvent and humid resistance, and excellent mechanical flexibility. The combination of processability and performance in these PFCB-containing thermoset materials make them as ideal candidates for the fabrication of high-performance polymeric planar lightwave circuit components with the applications in the telecom and datacom optical networks.
Encapsulated by highly-fluorinated dendrons, a nonlinear optical chromophore core, which is based on the phenyl-tetracyanobutadienyl (Ph-TCBD) thiophene-stilbene-based NLO chromophore, exhibits a large ~30-40 nm blue shift of the charge-transfer absorption maximum, 20 oC higher decomposition temperature, and most impressively, three times higher E-O coefficient. The combination of these appreciable improvements makes the molecular design of dendritic modification as a very promising molecular-engineering for next generation of E-O materials.
A series of dendron-modified nonlinear optical (NLO) chromophores and multiple chromophore-containing crosslinkable NLO dendrimers have been developed. The enhancement of poling efficiency (40%) in the dendritic NLO chromophore/polymer guest/host system was obtained due to the significant minimization of intermolecular electrostatic interactions among chromophores by the dendritic effect. Multiple NLO chromophore building blocks can be further placed into a dendrimer to construct precise molecular architecture with predetermined chemical composition. The site-isolation effect, through the encapsulation of NLO moieties by dendrons, can greatly enhance the performance of electro-optic (E-O) materials. A very large E-O coefficient (r33=60 pm/V at 1.55 micrometers ) and high temporal stability (85 degree(s)C for more than 1000 h) were achieved in a NLO dendrimer developed through the double-end functionalization of a 3D shape phenyl-tetracyanobutadienyl (Ph-TCBD)- containing NLO chromophore with thermally crosslinkable trifluorovinylether-containing dendrons.
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