Synthesis and Characterization of Electropolymerized Porphyrin Nanofibers
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1013-Z04-07
Synthesis and Characterization of Electropolymerized Porphyrin Nanofibers Michael G. Walter and Carl C. Wamser Chemistry, Portland State University, P. O. Box 751, Portland, OR, 97207-0751
ABSTRACT Electrochemical oxidation of tetrakis-5,10,15,20-(4-aminophenyl)porphyrin (TAPP) on fluorine-doped tin oxide electrodes leads to a conductive polymeric film (poly-TAPP) with a nanostructured fibrous morphology. The nanofiber structure and growth rate are enhanced by the addition of pyridine (5 - 15%) to the dichloromethane electrochemical solution. Electropolymerization in the absence of pyridine leads to a more highly bundled poly-TAPP structure with a spectrum indicative of protonated porphyrin units. Testing of poly-TAPP electrodes in an electrochemical iodide cell and in a 1-(3-methoxycarbonyl)propyl-1phenyl[6,6]C61 (PCBM) integrated solid state photovoltaic cell indicates modest photoactivity. INTRODUCTION Porphyrins and porphyrin-containing materials continue to attract a great deal of attention for organic photonic devices because of their versatile molecular framework, varied optoelectronic properties, and strongly light-absorbing chromophores.1 The electropolymerization of porphyrins offers the advantage of controlling the film deposition and conductivity through varying porphyrin monomer, the potential window, and the electrolytic conditions.2 Figure 1 depicts the oxidative linkage of two TAPP monomers to the dihydrophenazine/phenazine structures proposed in poly-TAPP. We report a method to obtain a
Figure 1. Oxidative coupling of TAPP to diphenylamine, dihydrophenazine, or phenazine linkages. nanofibrous poly-tetrakis(4-aminophenyl)porphyrin (poly-TAPP) network electrochemically deposited from a dichloromethane/pyridine solution using cyclic voltammetry with a 30 s vertex delay. We demonstrate that by altering the solvent composition and electrodeposition method
the porphyrin film network structure and optoelectronic properties can be adjusted. Film morphology was studied using SEM/AFM microscopy while the porphyrin film deposition rates were studied using an electrochemical quartz crystal microbalance. The photoactivity of the films was measured in an iodide/triiodide electrochemical cell and in a bilayer PCBM integrated solid-state cell for determining their potential role in an organic/inorganic solar cell. EXPERIMENTAL The electropolymerization of tetrakis-5,10,15,20-(4-aminophenyl)porphyrin (TAPP) is carried out on a fluorine-doped SnO2 glass electrode (FTO, Pilkington North America, TEC 15) in a three-probe electrochemical cell using a 1 cm2 Pt foil counter electrode and Ag/AgNO3 reference electrode. Solutions were prepared with 0.15 mM TAPP used as received from TCI America with 10 mM tetrabutylammonium perchlorate (TBAP) as supporting electrolyte in a 95:5 or 85:15 (v:v) dichloromethane:pyridine deaerated solution. A combination of cyclic voltammetry (-0.3 to +0.7 V vs. Ag/AgNO3) and fixed potentiometry is used with a 30 s vertex delay at +0.7 V within each cycle. The resultant polyporp
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