In thicker films, the color produced by reaction with βnaphthol is dramatic and visible (Figure ). Estimation of the surface coverage of coupled β-naphthol from the film's absorbance using an estimated molar absorptivity of 2.5x10 gives a value on the order of 1x10 -9 mol/cm 2 . Ferrocene coverage of a film prepared under similar conditions is 5.7x10 - 10 mol/cm 2 , reasonably close to the β-naphthol coverage; the difference between these values most likely falls within the uncertainty of the two measurement techniques. The difference in surface coverages may also be due to the difference in surface coupling efficiencies or variation between the films from experiment to experiment.