Nowadays best single molecule rectifiers[1] exhibit limited performances, with typical rectification ratios lower than one order of magnitude.[2] In previous works,[3, 4] we focused on the Fermi level alignment problem in molecular junctions, more particularly the characterization of the Fermi level pinning phenomenon,[5, 6] at the theoretical level. We showed that this effect has a deep influence on the response of the transmission spectrum to an applied bias. Indeed, the Fermi level pinning leads to a control and a splitting of the energy levels coupled to their respective electrodes. This is at the origin of a consequent orbital polarization effect.[3, 4] Relying on our characterization of these effects, we introduce here three simple rules to design an efficient rectifying molecule, and demonstrate its functioning at the theoretical level, using the NEGF-DFT technique.[7] The design rules notably require both the introduction of asymmetric anchoring moieties and a decoupling bridge. They lead to a new rectification mechanism based on the compression and control of the HOMO/LUMO gap by the electrode Fermi levels, arising from a pinning effect. Significant rectification ratios up to two orders of magnitude can easily be obtained and are theoretically predicted, as the mechanism opposes the resonant to the non-resonant tunneling transport mechanisms. 1. Aviram, A. and M.A. Ratner, Molecular rectifiers. Chem. Phys. Lett., 29: 277-283 (1974) 2. Díez-Pérez, I., et al., Rectification and stability of a single molecular diode with controlled orientation. Nat Chem, 1: 635-641 (2009) 3. Van Dyck, C., et al, Fermi Level Pinning and Orbital Polarization Effects in Molecular Junctions: The Role of Metal Induced Gap States. Adv. Funct. Mat., 24: 6154-6165 (2014) 4. Van Dyck, C., et al., Impact of derivatization on electron transmission through dithienylethene-based photoswitches in molecular junctions. PCCP, 15: 4392-4404 (2013) 5. Kim, B., et al., Molecular Tunnel Junctions Based on π-Conjugated Oligoacene Thiols and Dithiols between Ag, Au, and Pt Contacts: Effect of Surface Linking Group and Metal Work Function. JACS, 133: 19864-19877 (2011) 6. Sayed, S.Y., et al., Charge transport in molecular electronic junctions: Compression of the molecular tunnel barrier in the strong coupling regime. PNAS, 109: 11498-11503 (2012) 7. Van Dyck, C. and M.A. Ratner, Molecular Rectifiers: A New Design Based on Asymmetric Anchoring Moieties. Nano Letters, 15: 1577-1584 (2015)

Molecular rectifiers: Role of the Fermi level alignment and new design based on asymmetric anchoring moieties

251st National Meeting (2016)

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