Reversible quantum confinement of polarons by reaction of protonated emeraldine with nitric oxide

Nitric oxide (NO), a free radical, adds to green emeraldine acid, a polyradical and a one-dimensional polaronic conductor. As more NO is added, the segments through which protons and their associated unpaired electrons move, i.e., the polarons, are progressively shortened. This confinement of polarons is observed as a spectral progression from the parent green emeraldine acid, with an absorption maximum at 875 nm, to a series of blue polymers, their absorption maxima shifting progressively while decreasing in intensity with NO uptake to 670 nm, then turning colorless, with only a faint residual absorption at lambda (max) = 625 nm for the end member of the series which is insulating and no longer shows a voltammetric wave. The sequence is reversed in dilute HCl where the colorless and insulating polymer releases nitric oxide, the polaron is deconfined and the voltammetric wave reappears.