Morphology of Rhenium Complex-Containing Polystyrene-<i>b</i><i>lock</i>-poly(4-vinylpyridine) and Its Use as Self-Assembly Templates for Nanoparticles

Polystyrene-block-poly(4-vinylpyridine) was functionalized with a chlorotricarbonyl rhenium(I) diimine complex. Compared to the metal-free copolymer, the copolymer−metal complex exhibited different morphologies, which are highly sensitive to the solvent used for spin-coating and the surface properties of the substrates. Well-defined cylindrical or spherical domains were observed. Due to its ionic nature, the poly(4-vinylpyridine)−rhenium complex block could also serve as a template for subsequent deposition of cadmium sulfide nanoparticles by electrostatic attraction. The pattern of the deposited nanoparticles was found to be the replica of the block copolymer underneath, and their presence on the film surface was confirmed by X-ray photoelectron spectroscopy

Nanosized Micelles Formed by the Self-assembly of Amphiphilic Block Copolymers with Luminescent Rhenium Complexes

We have synthesized a series of polystyrene-block-poly(4-vinylpyridine)s (PS-b-PVP) to which luminescent tricarbonyl(2,2‘-bipyridyl)rhenium(I) complexes were attached. The rhenium complexes could induce the self-assembly of the copolymers into nanosized micelles with different shapes and dimensions, depending on the block size distribution of the copolymers and the solvent system being used. In general, spherical micelles were observed when methanol, a nonsolvent for the polystyrene block, was added to a copolymer solution in dichloromethane. Micellization was observed when the added methanol concentration was approximately 30%. When toluene, a nonsolvent for the poly(4-vinylpyridine) block, was added to the copolymer solution in dichloromethane, micelles with different interesting shapes were observed. For copolymers with larger PVP block size, spherical micelles were observed. When the relative block size of the PVP block was reduced, the micelles gradually changed to disk or vesicle structures and then to rodlike structures. The rhenium complex can act as a luminescent probe in the resulting nanosized micelles and provide sufficient contrast for electron microscopic studies. Significant changes in luminescence spectra were observed after the micellization

Synthesis and Properties of Polyimide with Diazacrown Ether Moiety and the Corresponding Polymer Barium Complexes

A series of polyimides with diaza-18-crown-6 moieties on the main chain were synthesized by the reaction between 4,4‘-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and different macrocyclic diamine monomers. The polyimide barium complexes were also synthesized from the corresponding monomeric barium complexes. An X-ray crystal structure of one of the monomers was also determined. Good quality, free-standing polymer films were obtained by thermal imidization of the poly(amic acid) presursors. No decomposition of the barium complexes was found during the thermal imidization processes. The polyimides and their barium complexes exhibit different electronic absorption properties, which is attributed to the formation of charge-transfer excited states. The binding of barium ion to the polymer main chain may affect the energy level of the resulting charge transfer states. In addition, the emission properties of the polyimides with and without barium ion are also different. Changes in the emission spectrum were observed when the metal-free polyimide film was immersed in barium solution. These materials may serve as potential candidates as sensors for barium or other alkaline earth metals

Exceptional Oxygen Sensing Capabilities and Triplet State Properties of Ir(ppy-NPh₂)₃

Exceptional Oxygen Sensing Capabilities and Triplet State Properties of Ir(ppy-NPh2)3</sub

Accurate Determination of the Index of Refraction of Polymer Blend Films by Spectroscopic Ellipsometry

To model the performance of a bulk-heterojunction solar cell, it is necessary to obtain information about the index of refraction of the blend layer, which is typically determined by spectroscopic ellipsometry measurements. The optical functions of poly(3-hexylthiophene)−[6,6]-phenyl C61-butyric acid methyl ester (P3HT−PCBM) blend films have been extensively studied. However, there is a large variation of the reported optical functions in the literature. Because of this fact, as well as the widespread use of P3HT−PCBM films in organic photovoltaics, we have selected this material system as an example and performed a detailed analysis of spectroscopic ellipsometry data. We illustrate the occurrence of multiple solutions and the importance of a dedicated methodology to reach a satisfactory unique solution. The proposed methodology involves the following steps: (1) multisample analysis; (2) independent thickness and surface characterization; (3) use of the adequate optical description of substrate; (4) thickness estimation from transparent range using Cauchy model; (5) fitting n and k in the entire range with fixed thickness; verify result is physically meaningful; (6) optimization of the parameters to be fitted; (7) repeating steps 5 and 6 with and without EMA layer to account for the surface roughness; (8) finally, and only if no satisfactory fit could be obtained from previous steps, attempts to introduce anisotropy, graded layers, or other nonideal models should follow

Fabrication and Optoelectronic Properties of Novel Films Based on Functionalized Multiwalled Carbon Nanotubes and (Phthalocyaninato)Ruthenium(II) via Coordination Bonded Layer-by-Layer Self-Assembly

4-(2-(4-pyridinyl)Ethynyl)benzenic diazonium salt (PBD) was used to modify multiwalled carbon nanotubes (MWCNTs) by the self-assembly technique. After the decomposition of the diazonium group in PBD under UV irradiation, the PBD monolayer film covalently anchored on multiwalled carbon nanotubes is very stable. The obtained pyridine-modified MWCNTs (Py(Ar)-MWCNTs) have good solubility in common organic solvents. Furthermore, the layer-by-layer (LBL) self-assembled fully conjugated films of Py(Ar)-MWCNTs and (phthalocyaninato)ruthenium(II) (RuPc) were fabricated on the PBD-modified substrates, and characterized using UV−vis absorption spectroscopy, scanning electron microscopy (SEM), and electrochemistry. The UV−vis analysis results indicate that the LBL RuPc/Py(Ar)-MWCNTs self-assembled multilayer films with axial ligands between the ruthenium atom and pyridine group were successfully fabricated, and the progressive assembly runs regularly with almost equal amounts of deposition in each cycle. A top view SEM image shows a random and homogeneous distribution of Py(Ar)-MWCNTs over the PBD-modified silicon substrate, which indicates well independence between all Py(Ar)-MWCNTs. Moreover, the opto-electronic conversion was also studied by assembling RuPc/Py(Ar)-MWCNTs multilayer films on PBD-modified ITO substrate. Under illumination, the LBL self-assembled films on ITO showed an effective photoinduced charge transfer because of their conjugated structure and the ITO current density changed with the number of bilayer. As the number of bilayers was increased, the photocurrent increases and reaches its maximum value (∼300 nA/cm2) at nine bilayers. These results allow us to design novel materials for applications in optoelectronic devices by using LBL self-assembly techniques

Ruthenium Complex Containing Block Copolymer For the Enhancement of Carbon Nanotube Photoconductivity

We report the synthesis of a multifunctional block copolymer incorporated with pyrene and ruthenium terpyridyl thiocyanato complex moieties by reversible addition–fragmentation chain transfer polymerization. The pyrene block in the copolymer facilitates the dispersion of multiwalled carbon nanotubes in DMF solution because of the strong π–π interaction between the pyrene moieties and nanotube surface. On the other hand, the ruthenium complexes greatly enhance the photosensitivity of the functionalized nanotubes in the visible region. The photocurrent responses of the nanotubes at different wavelength measured by conductive AFM spectrum strongly agree with the absorption spectrum of the ruthenium complex. The results demonstrate a new and versatile approach in enhancing and fine-tuning the photosensitivity or other opto-electronic properties of carbon nanotubes by multifunctional block copolymers

Annealing of P3HT:PCBM Blend FilmThe Effect on Its Optical Properties

Annealing is a common method to improve the efficiency of polymer photovoltaic cells. Annealing changes the microphase separation in a polymer blend film and typically also results in a change in its optical properties. We investigated the optical properties of poly­(3-hexyl­thiophene) (P3HT):[6,6]-phenyl C₆₁ butyric acid methyl ester (PCBM) before and after thermal annealing using spectroscopic ellipsometry and transmission measurements, with simultaneous fitting of samples with different thicknesses to ensure reliability of extracted index of refraction values. We found that, after annealing, it is necessary to consider an anisotropic model to describe the properties of P3HT:PCBM blend films, which reflects the increased order of P3HT chains as a result of annealing. Different fitting models (simple anisotropic layer, graded isotropic, graded anisotropic model, generalized oscillator, and oscillator model including Huang–Rhys vibronic envelope) have been compared and discussed. The effect of the number of samples used for fitting and surface roughness corrections is also discussed

Control of Electron Flow Direction in Photoexcited Cycloplatinated Complex Containing Conjugated Polymer–Single-Walled Carbon Nanotube Hybrids

Conjugated polymers incorporated with cycloplatinated complexes <b>(P1–Pt</b> and <b>P2–Pt</b>) were used as dispersants for single-walled carbon nanotubes (SWCNTs). Significant changes in the UV–vis absorption spectra were observed after the formation of the polymer/SWCNT hybrids. Molecular dynamics (MD) simulations revealed the presence of a strong interaction between the cycloplatinated complex moieties and the SWCNT surface. The photoinduced electron transfer processes in these hybrids were strongly dependent on the type of the comonomer unit. Upon photoexcitation, the excited <b>P1–Pt</b> donates electrons to the SWCNT, while <b>P2–Pt</b> accepts electrons from the photoexcited SWCNT. These observations were supported by results from Raman and femtosecond time-resolved transient absorption spectroscopy experiments. The strong electronic interaction between the Pt complexes and the SWCNT gives rise to a new hybrid system that has a controllable photoinduced electron transfer flow, which are important in regulating the charge transport processes in SWCNT-based optoelectronic devices

Splitting Water on Metal Oxide Surfaces

We have identified a class of metal oxide surfaces that are very effective in dissociating water. These oxide surfaces are characterized by having their surface O 2p level lying significantly above the valence band maximum (VBM) and within the band gap. Density functional theory is used to determine the adsorption energy per water molecule and finds that water dissociates completely at all coverages on these surfaces. Fourier transform infrared (FTIR) spectroscopy is used to verify that there is little or no molecular water present on the surface. Besides splitting water, this class of metal oxide surfaces should also be effective in splitting other kinds of hydrogen compounds. By contrast, oxides whose surface O 2p level lies buried inside the valence band are much less reactive, and water adsorbs on these surfaces in molecular form