Electrochemistry of cofacial phthalocyanine polymers: What can we learn about how molecular metal collective properties respond to wide variations in band filling?

The oxidative electrochemistry of the cofacially joined phthalocyanine polymer [Si (Pc)O]_n to yield molecular "metals" with tunable band filling is described. Initial doping (oxidation) of orthorhombic [Si (Pc)O]_n is accompanied by a rearrangement to a tetragonal crystal structure. Once in the tetragonal crystal structure, the conduction band filling can be continuously varied (i.e. doping is homogeneous) over a broad range in y for {[Si (Pc)O]X_y∼_n. For example, materials incorporating BF^- ₄ as the counterion can be tuned between y = 0.0 and y = 0.50. In fact, the maximum doping level obtainable with a given counterion is largely a function of anion size. Charge transport, optical, and magnetic studies of the {[Si (Pc)O] (BF₄)_y∼_n materials reveal an evolution in properties from insulator/semiconductor-like to metal-like with increasing y and an abrupt insulator-to-metal transition at y ≈ 0.20. This change at y ≈ 0.20 appears to be an Anderson-like transition from localized (disordered) states to delocalized states. Physical measurements on {[Si (Pc)-O] (SO₄)_y∼_n show no evidence of exceptional electronic effects attributable to the dinegative counterion.