Comparison of the charge-transport rate in two redox levels of polymers derived from N,N'-dibenzyl-4,4'-bipyridinium and N,N'-dialkyl-4,4'-bipyridinium

Charge transport in electrode-confined polymers derived from N,N'-bis(p-(trimethoxysilyl)benzyl)-4,4'-bipyridinium dichloride, ((BPQ/sup 2+/+/0/)/sub n/)/sub surf/, and N,N'-bis((trimethoxysilyl)propyl)-4,4'-bipyridinium dibromide, ((PQ/sup 2+/+/0)/sub n/)/sub surf/, has been studied. Specifically, a comparison of charge transport in the 2+/+ and +/0 redox systems of both polymers has been made. Interestingly, +/0 has an effective diffusion coefficient for charge transport, D/sub CT/, that is significantly greater than that for the 2+/+ redox level in H/sub 2/O/CH/sub 3/CN (9/1 by volume) 1.0 M LiCl. Platinum disk electrodes have been studied that have polymer thicknesses up to approx. 2.5 ..mu..m in the 2+ state corresponding to a coverage of approx. 7.5 x 10/sup -7/ mol of monomer units per cm/sup 2/. Up to a 30-40% decline in thickness is observed upon reducing the polymer from the 2+ to the 0 state. Values of the products D/sub CT/C/sup 2/, where C is the concentration of monomer units in the + or 0 state of the polymer, have been determined by measuring the current for reduction of Ru(NH/sub 3/)/sub 6//sup 3 +/ at polymer-coated rotating disks as a function of polymer coverage. The data support the conclusion that >20 mA/cm/sup 2/ can be maintained when the polymer thickness in the 2+ statemore » is 1.0 ..mu..m, corresponding to a coverage of approx. 2 x 10/sup -7/ mol/cm/sup 2/ of monomers per cm/sup 2/. 10 references, 7 figures, 1 table.« less