Zirconium Phosphonate Multilayers of Organic Redox Couples on Nanocrystalline TiO2 Semiconductor Electrode

New type of surface modification of redox-couple multilayers on nanoporous TiO 2 film has been demonstrated. N,N′-bis(ethylphosphonic acid)-4,4′-bipyridinium chloride(VP) and N,N′-bis(ethyl dihydrogen phosphate)-3,4,9,10-perylene bis(dicarboximide)(EPPI) were directly coordinated at surface defect site Ti 4+ of nanoporous TiO 2 film electrode. The sequential adsorption by alternating treatment of ZrOCl 2 and VP or EPPI allows building up zirconium phosphonate multilayers of the redox couples. Cyclic voltammetry and UV-visible absorption measurement have shown the systematic layer-by-layer growing of the multilayers and the heterogeneous electron-transfer from TiO 2 conduction band to the redox couples multilayers. The estimated average amount of the redox couples in each layer on the electrode was about 1.0 × 10 −11 mole/cm 2 which is in agreement with the reported density of states assigned to surface Ti 4+ sites.