ORGANIC DIODES BASED ON REDOX-POLYMER BILAYER-FILM-MODIFIED ELECTRODES

The synthesis of four electropolymerizable 2,2'-bipyridinium salts wit h tuned reduction potential (E(1) degrees) is described (N,N'-ethylene -4-methyl-4'-vinyl-2,2'-bipyridinium dibromide (4; E(1) degrees = -0.4 8 V), thyl-N,N'(trimethylene)-4'-vinyl-2,2'-bipyridinium dibromide (5; E(1) degrees = -0.66 V), thyl-4'-[2-(1H-pyrroll-yl)ethyl]-2,2'-bipyri dinium bis(hexafluorophosphate) (6b; E(1) degrees = -0.46 V),, and -1- yl)ethyl]-N,N'-(trimethylene)-2,2'-bipyridinium bis(hexafluorophosphat e) (7b; E(1) degrees = -0.66 V)). E(1) degrees-Tuning is based on the torsional angle C(3)-C(2)-C(2')-C(3'), imposed by the N,N'-ethylene an d N,N'-(trimethylene) bridge. The vinylic compounds 4 and 5 undergo ca thodic, the pyrrole derivatives 6b and 7b anodic electropolymerization on glassy carbon electrodes from MeCN solutions, yielding thin, surfa ce-confined films with surface concentrations of redox-active material in the range 5.10(-9) < Gamma < 2.10(-8) mol/cm(2), depending on expe rimental conditions. The modified electrodes exhibit reversible 'diqua t' electrochemistry in pure solvent/electrolyte. Copolymerization of 6 b or 7b with pyrrole yields most stable electrodes. Bilayer-film-modif ied electrodes were prepared by sequential electropolymerization of th e monomers. The assembly electrode/poly-6b/poly-7b behaves as a switch , it transforms - as a Schmitt trigger - an analog input signal (the e lectrode potential) into a digital output signal (redox state of the o uter polymer film). Forward-(electrode/pory-7b/poly-6b) and reverse-bi ased assemblies (electrode/ poly-6b/poly-7b) were coupled to the elect rochemical reduction of redox-active solution species, e.g. N-(cyanome thyl)-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 dis cussed in terms of molecular electronic devices.