EFFICIENT LATERAL ELECTRON-TRANSPORT INSIDE A MONOLAYER OF AROMATIC-AMINES ANCHORED ON NANOCRYSTALLINE METAL-OXIDE FILMS

A monolayer of a phosphonated triarylamine adsorbed on nanocrystalline TiO2, ZrO2, or Al2O3 film deposited on conducting glass displays reve rsible electrochemical and electrochromic behavior although the redox potential of the electroactive molecules (0.80 V vs NHE) lies in the f orbidden band of the semiconducting or insulating oxides. The mechanis m of charge transport was found to involve hole injection from the con ducting support followed by lateral electron hopping within the monola yer. The apparent diffusion coefficient ranged from 2.8 x 10(-12) m(2) s(-1) in the neat 1-ethyl-2-methylimidazolium bis(trifluoromethylsulf onyl)imide (EtMeIm(+)Tf(2)N(-)) to 1.1 x 10(-11) m(2) s(-1) in acetoni trile + 2 M EtMeIm(+)Tf(2)N(-). A percolation threshold for electronic conductivity was found at a surface coverage corresponding to 50% of a full monolayer.