No abstract

Summary: The synthesis of a hyperbranched polymer containing a rhenium bipyridine complex is reported. The polymer was synthesized from a monomer that contains two chlorotricarbonyl rhenium(I) bipyridine moieties and a stilbazole ligand, and the polymer was formed by the coordination reaction in one single step. Gel permeation chromatography results showed that the resulting polymer had a strong interaction with the column packing material, which was reduced when the eluent was added with an electrolyte. Both atomic force microscopy and laser light scattering showed that the size of the polymer molecules was in the range between 25–30 nm. A monolayer of polymer molecules could form on a pretreated substrate by the self‐assembly process, which can serve as the building block for multilayer ultrathin film devices.The metal‐containing hyperbranched polymer synthesized here.magnified imageThe metal‐containing hyperbranched polymer synthesized here.

We report the synthesis and photosensitizing properties of various polystyrene and poly-(methyl methacrylate) that contain metal complex cores. The polymers were synthesized by atom transfer radical polymerization (ATRP) using metalloinitiators based on rhenium and ruthenium diimine complexes. The detailed structures of the initiators were determined by X-ray crystallography. In ATRP, the catalyst systems were composed of copper(I) bromide and 1,1,4,7,7-pentamethyldiethylenetriamine. The rates of polymerization depended on several factors such as the amounts of initiator, copper bromide, and ligand with respect to the monomer concentration. From the kinetic plots, the polymerizations showed first-order kinetics with respect to the monomer concentration, and the typical rate of polymerization is on the order of 10 -5 s -1 . The photoconducting properties of the polymers were studied using argon-ion laser (488 nm) as the light source. The metal complex cores may serve as efficient photosensitizers in the visible region, and the photoconductivities of the polymers are on the order of 10 -10 Ω -1 cm -1 . The experimental quantum yields were fitted into Onsager's equation, from which the primary yield and thermalization distance were calculated to be 0.02 and 1.3 to 1.8 nm, respectively.

Multilayer thin films were prepared by the layer‐by‐layer (LBL) deposition method using a rhenium‐containing hyperbranched polymer and poly[2‐(3‐thienyl)ethoxy‐4‐butylsulfonate] (PTEBS). The radii of gyration of the hyperbranched polymer in solutions with different salt concentrations were measured by laser light scattering. A significant decrease in molecular size was observed when sodium trifluoromethanesulfonate was used as the electrolyte. The conditions of preparing the multilayer thin films by LBL deposition were studied. The growth of the multilayer films was monitored by absorption spectroscopy and spectroscopic ellipsometry, and the surface morphologies of the resulting films were studied by atomic force microscopy. When the pH of a PTEBS solution was kept at 6 and in the presence of salt, polymer films with maximum thickness were obtained. The multilayer films were also fabricated into photovoltaic cells and their photocurrent responses were measured upon irradiation with simulated air mass (AM) 1.5 solar light. The open‐circuit voltage, short‐circuit current, fill factor, and power conversion efficiency of the devices were 1.2 V, 27.1 μ A cm−2, 0.19, and 6.1×10−3 %, respectively. The high open‐circuit voltage was attributed to the difference in the HOMO level of the PTEBS donor and the LUMO level of the hyperbranched polymer acceptor. A plot of incident photon‐to‐electron conversion efficiency versus wavelength also suggests that the PTEBS/hyperbranched polymer junction is involved in the photosensitization process, in which a maximum was observed at approximately 420 nm. The relatively high capacitance, determined from the measured photocurrent rise and decay profiles, can be attributed to the presence of large counter anions in the polymer film.

We report the polymerization of rhenium-containing methacrylates by atom transfer radical polymerization. The structure of the monomer was confirmed by X-ray crystallography, which showed the bulkiness of the metal-complex moiety. The rhenium complexes were polymerized in the presence of copper(I) bromide, 1,1,4,7,7-pentamethyldiethylenetriamine, and methyl 2-bromopropionate. They were copolymerized with methyl methacrylate in different monomer ratios. An ABA triblock copolymer was also synthesized with poly(methyl methacrylate) as the macroinitiator. When 2,2Ј-bipyridine was used as the ligand for the copper catalyst in the polymerizations, it underwent a ligand exchange process with the iminopyridine ligand in the monomer. The neutral rhenium complex in the homopolymers and copolymers could be converted into ionic forms by the replacement of the chloride with an imidazole ligand, and the solubility of the resulting ionic polymers was greatly enhanced. The photosensitizing properties of the doped and undoped polymer films were investigated by the measurement of the photocurrent response under an externally applied electric field. The photoconductivities of the polymers were approximately 10 Ϫ12 -10 Ϫ13 ⍀ Ϫ1 cm Ϫ1 . The experimental quantum efficiencies were simulated with Onsager's theory, and they showed that the initial quantum yield and thermalization distance were 10 Ϫ3 and 1.7 nm, respectively. Transmission electron microscopy showed that the rhenium complexes aggregated to form domains with dimensions of approximately 20 -30 nm.