Molecular rectification

The area of photoinduced electron transfer in LB films has been estabUshed (75). The abiUty to place electron donor and electron acceptor moieties in precise distances allowed the detailed studies of electron-transfer mechanism and provided experimental support for theories (76). This research has been driven by the goal of understanding the elemental processes of photosynthesis. Electron transfer is, however, an elementary process in appHcations such as photoconductivity (77—79), molecular rectification (79—84), etc. 

Ashwell GJ, Tyrrell WD, Whittam AJ (2005) Molecular rectification self-assembled monolayers in which donor-(7i-bridge)-acceptor moieties are centrally located and symmetrically coupled to both gold electrodes. J Am Chem Soc 126 7102-7110... 

Chabinyc ML, Chen X, Holmlin RE, Jacobs H, Skulason H, Frisbie CD, Mujica V, Ratner MA, Rampi MA, Whitesides GM (2002) Molecular rectification in a metal-insulator-metal junction based on self-assembled monolayers. J Am Chem Soc 124 11731-11736... 

Mujica V, Ratner MA, Nitzan A (2002) Molecular rectification why is it so rare Chem Phys 281 147-150... 

Okazaki N, Sambles JR, Jory MJ, Ashwell GJ (2002) Molecular rectification at 8 K in an Au I C16H33Q-3CNQ LB film I Au structure. Appl Phys Lett 81 2300-2302... 

Brady AC, Hodder B, Martin AS, Christopher JR, Ewels P, Jones R, Briddon PR, Musa AM, PanettaCA, Mattem DL (1999) Molecular rectification with MI(D-s-A LB film)IM junctions. J Mater Chem 9 2271-2275... 

Ashwell GJ, Robinson BJ, Amiri MA, Locatelli D, Quici S, Roberto D (2005) Dipole reversal in Langmuir-Blodgett films of an optically nonlinear dye and its effect on the polarity for molecular rectification. J Mater Chem 15 4203-4205... 

Nijhuis CA, Reus WF, Whitesides GM (2009) Organometallic molecular rectification in metal-SAM-metal junctions. J Am Chem Soc 131 17814-17827... 

Figure 11. 35 Molecular rectification (a) Flow of electrons, (b) No current unless V is sufficiently large. Steps 1, 2 and 3 are tunnelling processes.

There have been some impressive, relatively recent examples of molecular rectification. Compound 11.52 has proved to be an extremely efficient molecular rectifier, able to actually function as a rectification device by intramolecular tunnelling either as a monolayers or multilayer macroscopic film or on a nanoscopic level.51 Switchable rectification has been demonstrated for a related dye shown in Figure 11.36. The electrical asymmetry can be chemically switched, off and then back on, by treatment with acid and base, respectively. Protonation disrupts the intramolecular charge-transfer axis, destroying the rectification effect.52 Recent calculations, however, suggest that there may be relatively unpromising theoretical limits on the rectification possible by a single molecule.53... 

Armstrong, N., Hoft, R. C., McDonagh, A., Cortie, M. B., Ford, M. J., Exploring the performance of molecular rectifiers Limitations and factors affecting molecular rectification. Nano Letters 2007, 7, 3018-3022. 

Fig. 12.11 An experimental setup for the measurement of molecular rectification by HDQ-3CNQ. The electrical contact is established using a Ga/ln alloy in order to maintain the same electrical conditions at both electrodes. From [17].

Different approaches to bridge the size gap between conventionally fabricated circuit elements and truly atomic scale components have been discussed. These indude the use of electron transport through single molecules, the concept of molecular rectification, and the design of atomic relays or molecular shuttles. Today, the approach that receives the most attention among the different concepts of futuristic drcuit design is drcuitry based on single-electron transistors. 

S. Roth, M. Burghard, G. M. Fischer, Resonant tunneling and molecular rectification in Langmuir-Blodgett films in Molecular Electronics (Eds. J. Jortner, M. Ratner), Blackwell Science, Oxford, 1997, pp. 255-280. 

Figure 5.8. Schematic representation (a) of the experimental set-up used to verify molecular rectification in a donor-rr -acceptor molecule the electrode (-h) for the positive bias and the direction of an easy electron flow for V > 0 are marked, (b) Demonstration of rectification through a single monolayer sandwiched between AI electrodes. The DC voltage is swept at a rate of 10 mV/s and the DC current versus applied DC voltage is shown on a linear (c) and logarithmic scale (d). (From R. Metzger, B. Chen, U. Hopfner M. Lakshmikantham, D. Vuillaume T. Kawai, XL Wu, H. Tachibana, T. Hughes, H. Sakurai, J. W. Baldwin, C. Hosch, M. Cava, L. Brehmer, Journal of the American Chemical Society. 119(43).T0455 (1997))...

Kleverlaan C., Alebbi M., Argazzi R., Bignozzi C.A, Hasselmann G.M., Meyer G.J. Molecular rectification by a bimetallic Ru-Os compound anchored tonanocrystalline Ti02. Inorg. Chem. 2000 39 1342-1343... 

V. P. S. Tennakone, K. Molecular rectification application in dye-sensitized solar cells. Langmuir 2005, 21, 2997-3001. 

Wenbo E, Kadlsh KM, Sintic PJ, Khouty T, Govenlock LJ, Ou Z, Shao J, Ohkubo K, Reimers JR, Fukuzumi S, Crossley MJ (2008) Control of the orbital delocalization and implications for molecular rectification in the radical anions of praphyrins with coplanar 90° and 180° p, P -fused extensions. J Phys Chem A 112(3) 556-570. doi 10.1021/jp076406g Xu Z, Kim SK, Yoon J (2010) Revisit to imidazolium receptors for the recognition of anions highlighted research during 2006-2009. Chem Soc Rev 39(5) 1457—1466. doi 10.1039/ B918937H... 

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