The most popular wide band gap semiconductors, such as TiO₂ or ZnO, have (more or less) suitable electronic properties but their absorption is mostly confined to the ultraviolet region.  One of the opportunities to improve optical properties of wide band gap semiconductors is modification of the surface of particles. The most interesting materials, in point of view of optoelectronics, are hybrid materials showed photoelectrochemical photocurrent switching (PEPS) effect. This effect can be defined as switching of photocurrent polarity on change in photoelectrode potential and/or incident light wavelength. This effect was observed in some surface-modified TiO₂ materials [1-4].

Combination of 7,7',8,8'-tetracyanoquinodimethane (TCNQ), which is a good one-electron acceptor, with titanium dioxide (TiO₂) results new hybrid material with unique properties. The photosensitization effect is observed and the absorption range in this material reaches 550 nm. In the diffused reflectance spectra a new absorption peak was observed as a result of surface complex formation (Fig. 1).

Photoelectrodes prepared from this hybrid material exhibit the PEPS effect. Changing the wavelength or the photoelectrode potential easily switches the direction of photocurrent. At positive polarization of the photoelectrode only anodic photocurrent are observed as it can be expected for n-type semiconductor. At more negative potentials only cathodic photocurrent are observed.

Photoelectrochemical and spectroscopic studies allowed the elucidation of the mechanism of photocurrent switching. This mechanism is based on photoinduced electron transfer processes from TCNQ molecule to TiO₂ particle. Geometry and electronic structure calculations using DFT method confirmed this mechanism.

Photoelectrochemical properties of TCNQ@TiO₂ materials seem to be suitable for construction of simple logic gates or more advanced logic devices, such as demultiplexer [5-7].

[1] S. Gawęda, G. Stochel, K. Szaciłowski, Chem. Asian J. 2, 580-590 (2007)

[2] K. Szaciłowski, W. Macyk, M. Hebda, G. Stochel, ChemPhysChem, 7, 2384-2391 (2006)

[3] K. Szaciłowski, W. Macyk, W. Chimia, 61, 831-834 (2007)

[4] S. Gawęda, G. Stochel, K. Szaciłowski, J. Phys. Chem. C, 112, 19131–19141 (2008)

[5] A. Podborska, K. Szaciłowski, Austr. J. Chem. 63, 165-168 (2010)

[6] J. Mech, R. Kowalik, P. Kwolek, A. Podborska, K. Szaciłowski, Austr. J. Chem. 63, 1330-1333 (2010)

[7] S. Gawęda, R. Kowalik, P. Kwolek, W. Macyk, J. Mech, M. Oszajca, A. Podborska, K. Szaciłowski Isr. J. Chem., 51, 36–55 (2011)

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1. Nanofotoniczne układy logiczne
2. Unusual photoelectrochemical behaviour of surface-modified nanocrystalline semiconductors
3. Molecular Logic Gates