Wayne E. Jones

Toward transparent molecular wires: electron and energy transfer in transition metal derivatized conducting polymers

Abstract A great deal of research has concentrated on long range electron and energy transport in transition metal-based systems, including molecular donor-acceptor assemblies, electron and energy transfer cascades, dendrimers, and derivatized polymer systems. In an effort to improve efficiencies for electron and energy transport over large distances, several groups have now turned to conjugated systems. Several challenges exist to incorporating conducting materials/polymers in the study of photoinduced electron and energy transfer: solubility and processibility of the materials, thermal stability and limitations on direct spectroscopic characterization due to band gap absorptions. We have prepared a new series of conducting materials that provides for direct incorporation of chromophores and electrophores within the backbone of a conducting polymer. Energy transfer dynamics between conducting polymer bridges and porphyrin or metal-to-ligand charge transfer (MLCT) chromophores can be controlled through intermolecular interactions in solid vs solution samples. We have also developed a methodology to incorporate transmissive benzothiophene-type polymers such as polyisothianaphthene (PITN) within a copolymer assembly. These new materials are now being used to investigate long range electronic coupling and have potential applications that range from artificial photosynthesis to light emitting diodes.

Metalloporphyrin polymers bridged with conjugated cyano-substituted stilbene units

A new metalloporphyrin polymer in which the metalloporphyrin units are bridged edge to edge with cyano-substituted stilbene was synthesized from [5,15-bis(4-formylphenyl)-10,20-bis(mesityl) porphyrin] Zn(II) and 1,4-dihexyloxy-2,5-benzenediacetonitrile via the Knoevenagel condensation reaction. The synthesis and characterization of a new porphyrin monomer and polymer are presented. Based on UV-Vis absorption and fluorescence studies, electronic communication between the chromophore groups is low. The relatively high solubility of the materials provides for the preparation of polymer films by spin coating. The polymer film can be doped by FeCl3 and shows limited conductivity. The doped film is extremely stable in air and can be reversibly dedoped by reducing reagents such as NaBH4.

Synthesis of soluble conjugated metalloporphyrin polymers with tunable electronic properties

New linear conjugated porphyrin polymers are synthesized by a palladium-catalyzed cross-coupling reaction of [5,15- bis(ethynyl)-10,20-bis(mesityl)porphyrin]zinc and diiodobenzene derivatives; enhanced solubility of the conjugated porphyrin polymers is achieved by attachment of long alkyl ether or dialkyl amide groups to the aryl moiety, resulting in unambiguous characterization by 1H NMR, IR, GPC, UV–VIS and fluorescence spectroscopy; in addition, the introduction of alkyl ether (electron donor) or dialkyl amide (electron acceptor) results in significant modulation of the electronic properties of the conjugated porphyrin polymers owing to strong electronic coupling.