This paper reports the synthesis and opto-electronic properties of different conjugated polymers that contain the diimine complexes of ruthenium or rhenium. Conjugated poly(phenylene vinylene)s that contain aromatic 1,3,4-oxadiazole and 2,2'-bipyridine units on the main chain were synthesized by the palladium catalyzed olefinic coupling reaction. Other types of polymers based on 1,10-phenanthroline bis(2,2-bipyridyl) ruthenium(II) or chlorotricarbonyl rhenium(I) complexes were also synthesized by the same reaction. In general, these polymers exhibit two absorption bands due to the pi - pi transition of the conjugated main chain and the d-pi* metal-to-ligand charge-transfer transition of the metal complex. As a result, the photosensitivity of the polymers beyond 500 nm was enhanced. Charge-carrier mobility measurements showed that the presence of metal complexes could facilitate the charge-transport process, and the enhancement in carrier mobility was dependent on the metal content in the polymer. In addition, we have also demonstrated that the ruthenium complex could act as both photosensitizer and light emitter. Photovoltaic cells were constructed, and they were subjected to irradiation with a xenon arc lamp. Under illumination, the short circuit current and the open circuit voltage were measured to be 0.05 mAcm(-2) and 0.35 V, respectively. The polymers were fabricated into single-layer emitting devices, and light emission was observed when the device was subjected to forward bias. The maximum luminance was determined to be 300 cdm(-2), and the external quantum efficiency was approximately 0.05 to 0.2%. Although the efficiency was relatively low when compared with other devices based on organic materials, we have demonstrated the first examples of using transition metal complexes for both photovoltaic and light-emitting applications.
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.
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.
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