Conducting Polymetallorotaxanes:  Metal Ion Mediated Enhancements in Conductivity and Charge Localization

In this paper we describe polymers of two metallorotaxane systems, Rot( 1,M) and Rot( 2,M) (M = Zn 2+ or Cu 1+ ), which are formed by complexing a macrocyclic phenanthroline, a 5,5‘-bis([2,2‘-bithiophen]-5-yl)-2,2‘-bipyridine (ligand 1 ) or 5,5‘-bis(3,4:3‘,4‘-bis(ethylenedioxy)[2,2‘-bithiophen]-5-yl)-2,2‘-bipyridine (ligand 2 ), and Zn 2+ or Cu 1+ ions. The corresponding polymetallorotaxanes, PolyRot( 1,M) and PolyRot( 2,M), are produced by oxidative polymerization of Rot( 1,M) and Rot( 2,M). The investigations of the electrochemical, conducting, and optical properties of the metallorotaxanes and polymetallorotaxanes as well as related nonrotaxane polymers Poly( 1 ) and Poly( 2 ) are reported. The combined electrochemical and conductivity studies of PolyRot( 1,M) and PolyRot( 2,M) indicated that the polymetallorotaxane's redox and conducting properties were dramatically affected by the Lewis acidic and redox properties of the coordinated metal ions. The Lewis acidity produces charge localization and a redox conduction process in both polymetallorotaxane systems. The matching of the polymer and Cu 1+/2+ couple redox potentials in PolyRot( 2,Cu) resulted in a Cu 1+/2+ contribution to conductivity. The metal-free PolyRot( 1 ) and PolyRot( 2 ) were produced by extracting the metal ions, and these polymers reversibly bound Zn 2+ or Cu 2+ ions in solution. The Cu 2+ dopes the films of PolyRot( 2 ) and Poly( 2 ), which have lower oxidation potential than those of PolyRot( 1 ), to produce 10 6 −10 7 -fold conductivity increases. In the case of PolyRot( 1 ) and Poly( 1 ), the rotaxane structure was demonstrated to be key for reversible complexation of metal ions.