Journal article

Triarylamine on Nanocrystalline TiO2 Studied in Its Reduced and Oxidized State by Photoelectron Spectroscopy

The electronic and mol. structures of an electrochem. reduced and oxidized triarylamine layer (((3-ethyl(p-N,N-dimethylamino)phenyl)amino)propyl-1-phosphonic acid) adsorbed on a nanocryst. TiO2 film have been studied. Photoelectron spectroscopy (PES) measurements on electrochem. prepd. surfaces and d. functional theory (DFT) calcns. for the free triarylamine mol. were performed. The major electronic difference between the reduced and oxidized state of the triarylamine mols. appears on the N atom. In the PES measurement a shift of the N 1s signal of 1.5 eV toward higher binding energies was measured between triarylamine in its reduced and oxidized states. The mol. structure of the surface layer depends on the electrolyte used in the electrochem. prepn. The oxidized triarylamine mol. is pos. charged and must therefore be accompanied by a neg. counterion. The identity of the counterion influences electron transfer between adjacent mols., as explained by geometrical differences of the surface layer. During the measurements the PES N 1s signal was affected by the continuous x-ray illumination. Interestingly, a reversible photoredn. of the oxidized triarylamine was obsd. The effect is accounted for by x-ray induced electron hole-pair generation in the TiO2 and subsequent electron transfer from the TiO2 conduction band to the singly occupied MO of the adsorbed mol.


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