Organic Diodes Based on Redox-Polymer Bilayer-Film-Modified Electrodes

Article abstract of DOI:10.1002/hlca.19940770134

The synthesis of four electropolymerizable 2,2'-bipyridinium salts with tuned reduction potential (E⁰₁) is described (N,N'-ethylene-4-methyl-4'-vinyl-2,2'bipyridinium dibromide (4: E⁰₁=-0.48 V), 4-methyl-N,N'-(trimethylene)-4'-vinyl-2,2'-bipyridinium dibromide (5: E⁰₁=-0.66 V), N,N'-ethylene-4-methyl-4'-<2-(1H-pyrrol-1-yl)ethyl>-2,2'-bipyridinium bis(hexafluorophosphate) (6b: E⁰₁=-0.46 V), and 4-methyl-4'-<2-(1H-pyrrol-1-yl)ethyl>-N,N'-(trimethylene)-2,2'-bipyridinium bis(hexafluorophosphate) (7b: E⁰₁=-0.66 V)).E⁰₁-Tuning is based on the torsional angle C(3)-C(2)-C(2')-C(3'), imposed by the N,N'-ethylene and N,N'-(trimethylene) bridge.The vinylic compounds 4 and 5 undergo cathodic, the pyrrole derivatives 6b and 7b anodic electropolymerization on glassy carbon electrodes from MeCN solutions, yielding thin, surface-confined films with surface concentrations of redox-active material in the range 5*10^-9<Γ<2*10^-8 mol/cm², depending on experimental conditions.T he modified electrodes exhibit reversible 'diquat' electrochemistry in pure solvent/electrolyte.Copolymerization of 6b and 7b with pyrrole yields most stable electrodes.Bilayer-film-modified electrodes were prepared by sequential electropolymerization of the monomers.The assembly electrode/poly-6b/poly-7b behaves as a switch, it transforms -as a Schmitt trigger- an analog input signal (the electrode potential) into a digital output signal (redox state of the outer polymer film).Forward-(electrode/poly-7b/poly-6b) and reverse-biased assemblies (electrode/poly-6b/poly-7b) were coupled to the electrochemical reduction of redox-active solution species, e.g.N-(cyanomethyl)-N'-methyl-4,4'-bipyridinium bis(hexafluorophosphate) (8).Zener-diode-like behavior was observed.Aspects of redox-polymer multilayer-film assemblies, sandwiched between two electronic conductors, are discussed in terms of molecular electronic devices.