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

Abstract

Abstract The synthesis of four electropolymerizable 2,2′‐bipyridinium salts with tuned reduction potential ( E 1 ∘ ) is described ( N , N ′‐ethylene‐4‐methyl‐4′‐vinyl‐2,2′‐bipyridinium dibromide ( 4 ; E 1 ∘ –0.48 V), 4‐methyl‐ N , N ′‐(trimethylene)‐4′‐vinyl‐2,2′‐bipyridinium dibromide ( 5 ; E 1 ∘  −0.66 V), N,N′ ‐ethylene‐4‐methyl‐4′‐[2‐(1 H ‐pyrrol‐1‐yl)ethyl]‐2, 2′‐bipyridinium bis(hexafluorophosphate) ( 6b ; E 1 ∘  −0.46 V), and 4‐methyl‐4′‐[2‐(1 H ‐pyrrol‐1‐yl)ethyl]‐ N , N ′‐(trimethylene)‐2,2′‐bipyridinium bis(hexafluorophosphate) ( 7b ; E 1 ∘  −0.66 V)). E 1 ∘ ‐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/cm 2 , depending on experimental conditions. The modified electrodes exhibit reversible ‘diquat’ electrochemistry in pure solvent/electrolyte. Copolymerization of 6b or 7b with pyrrole yields most stable electrodes. Bi ayer‐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.