Solution Based Systems Initially No electrodes directly involved Rotaxanes Fraser Stoddard and co-workers eg early work: Pure &App/. Chem.,Vol. 65, No. 11, pp. 2351-2359,1993.
Important factors for the single molecule systems Molecular orbitals Interface Electrodes Nature Nanotech. 4 (9), 551-556, 2009 The chemical anchor point: controls the self-assembly and is of paramount importance for the nature of the electron transport
3.3 3.5 eV 2.5 2.8 eV 3.8 3.9 eV n sat = 10 n sat = 9n sat = 10n sat = 2 5.7 eV 2.3 eV 2.2 3.2 eV 1.4 1.8 eV n sat = 20 Optical band gaps for ”infinite” polymers obtained by extrapolation of monodisperse oligomers Calculation Molecular Back-bone: does it matter? Slide courtesy of prof. MB Nielsen, Univ. Copenhagen
Molecular Back-bone: does it matter? Kushmerik, TS Mayer and co-workers J. Phys. Chem. B 2004, 108, 2827-2832
Ferdinan Evers and co-workers small 2009, 5, No. 19, 2218–2223 “Switching Driven by rotation in the central bond in the bipyridine unit, induced by alignment of the dipoles in the Nitro groups with the electric field”
Mayor, Wandlowski and co-workers Nano Lett. 2010, 10, 156-163 Conductivity vs torsion angle Conductivity and torsion angle: detailed investigation
3.3 3.5 eV 2.5 2.8 eV 3.8 3.9 eV n sat = 10 n sat = 9n sat = 10n sat = 2 5.7 eV 2.3 eV 2.2 3.2 eV 1.4 1.8 eV n sat = 20 Optical band gaps for ”infinite” polymers obtained by extrapolation of monodisperse oligomers Calculation Electron delocalization via cross conjugation is less efficient than via linear conjugation Molecular Back-bone: does it matter? Slide courtesy of prof. MB Nielsen, Univ. Copenhagen
Cross-conjugation, where does it come from? It is all p z orbitals so why is the delocalization different? So surprizing that the physists has come up with their own name for it: “Quantum interference” Chemist might say: we have known about it all the time: ortho/para vs meta directing? Michael addition?
M. Mayor, H.B. Weber, J. Reichert, M. Albing, C. von Hänisch, D. Beckmann, M. Fischer, Angew. Chem. Int. Ed. 2003, 42, 5834-5838. Position of the Anchor Groups Smaller conductance (by 2 orders of magnitude) para: linear conjugation meta: cross conjugation
Switching via changes in electronic states: Cross Conjugation and Quantum Interference dx.doi.org/10.1021/ja202471m |J. Am. Chem. Soc. XXXX, XXX, 000–000 Hummelen and Solomon
Synthesis and initial Charactarisation: Hummelen and co-workers Org. Lett., 2006, 8 (11), pp 2333–2336 Transport and Thery „evidence of Quantum Interference” JACS ASAP 2011 dx.doi.org/10.1021/ja202471m Brønsted-Nielsen and co-workers Org. Lett. 2006 Vol. 8, No. 6 1173-1176 J. Org. Chem, Vol. 73, No. 8, 2008 Ox Red
D. Dulic, S. J. Van Der Molen, T. Kudernac, H. T. Jonkman, J. J. D. de Jong, T. N. Bowden, J. van Esch, B. L. Feringa, B. J. van Wees, Phys. Rev. Lett. 2003, 91, 207402. Conjugation/cross conjugation photoswitch
Methods of contacting molecules Scalability? Tunability of a nanogap? Single-molecule device possible? Possible artifacts Is gating possible? For industry or for research? How was it made? How was the molecules designed? What kind of switching? 5 min report (3 slides) + 1 A4 Written summary e-mail your presentation before oct 3 to firstname.lastname@example.org Seminar on Oct 5