Ultrathin and Nanostructured Organic Layers with on/Off Switching Properties Based on Covalently Grafted Olidothiophenes

Conducting surface modification by covalent attachment of organic molecules is needed in research fields such as molecular electronics. or smart surfaces. Among several methods leading to immobilisation of organic molecules onto a surface, one of the most frequent reactions is the electrochemical reduction of an aryl diazonium salt. We have used this method with several diazonium salts containing thiophene units. The resulting surfaces were characterized employing electrochemical measurements and X-ray photoelectron (XPS) analysis. The layers have thicknesses between 3 and 20 nm and are strongly attached to the surface as a result of covalent grafting. Unusual electrochemical responses towards several outer-sphere redox couples have been observed. In case of redox couples bearing a redox potential below a threshold potential, a diode-like behaviour was observed whereas for redox potentials superior to this threshold potential, the film becomes conducting and no modification of the electrochemical signal of the redox probes were observed when compared to bare electrodes. The threshold can be easily tuned by the molecular structure of the grafted oligomers. Ultrathin layer junctions based on conjugated oligomers with reversible on/off switching capabilities controled by the redox state of the oligomer have thus been obtained. 1, 2

Such diazonium salts can be easily included in cyclodextrine. We have shown that the electroreduction of the encapsulated diazonium salts in water solution leads to modified surfaces consisting of grafted oligothiophenes and cyclodextrins which can be removed from the surface.  Electroreduction of a second diazonium in the generated holes is possible and leads to mixed layers. 3, 4 Finally such films can be nanostructured using Nanosphere lithography and several nanostructured multifunctional layers can be generated using this inexpensive technique. 5

The use of such ultrathin, nanostructured and multifunctional organic layers will be discussed. 6

1 Fave C.; Noel V.; Ghilane J.; Trippe-Allard G.; Randriamahazaka, H., Lacroix J. C.   J. Phys. Chem. C (2008), 112(47), 18638

2 Stockhausen V.; Ghilane J.; Martin P., Trippe-Allard, G.; Randriamahazaka, H.; Lacroix J. C. JACS  (2009), 131(41), 14920.

3. Santos L.; Ghilane J.; Martin P.; Lacaze, P.-C.; Randriamahazaka, H.; Lacroix J. C. JACS, (2010) 132(5), 1690.

4. Santos L., Ghilane, J.; Lacroix J. C. JACS  (2012) 134 , 12, 5476-5479

5. Santos L.,  Ghilane, J.; Lacroix J. C Electrochemistry Communications (2012) 18, 20-23

6. Martin P.; Della Rocca, M. L. ; Anthore, A. ; Lafarge, P. ; Lacroix J. C. JACS  (2012) 134(1), 154-157. Yan, H.; Bergren, A. J.; McCreery, R.; Della Rocca, M. L.; Martin, P.; Lafarge, P.; Lacroix, J.C. PNAS, (2013) 110, 14, 5326-5330.