Unimolecular electronics

During the last decades the untenable growth of the number of transistors in an integrated circuit together with the increasing societal demand of computational power has revealed the need of a change of paradigm in the field of electronics. In this context Molecular Electronics aims at scaling down electronics to its ultimate limits by choosing single molecules as the building blocks of active devices. In this field functional molecules are utilized as the active (switching, sensing, etc.) or passive (current rectifiers, surface passivants) elements in electronic devices. The advantages of this approach are the high reproducibility of molecular synthesis on the nanometer scale and the ability of molecules to form large structures by self-assembly.

We have strong expertise in the design, synthesis and characterization of novel electroactive systems based on the use of multifunctional organic molecules (i.e. stable organic radicals, TTF derivatives, etc). We are focused on the electronic properties of these molecules as wires, switches or rectifiers in solution and also when they are immobilised on surfaces through self-assembled monolayers (SAMs). These later hybrid materials are key for the fabrication of potential operative nanotechnological devices. Here we describe briefly some of the lines that we are currently involved.

Molecular switches

Systems that can be reversibly converted between two stable states that differ in their physical properties are particularly attractive in the development of memory devices when immobilized in substrates. We are working now on fabricating highly robust surface-confined switches based on electroactive molecules (i.e. polychlorotriphenylmethyl radicals, tetrathiafulvalenes, etc) immobilized on conducting surfaces that can be electrochemically and reversibly converted between their different accessible redox states. In these molecular systems an electrical input is then transduced into optical as well as magnetic or chemical outputs under ambient conditions.molecularSwitches

For recent publications on this topic see:

  • C. Simão, M. Mas-Torrent, N Crivillers, V. Lloveras, J. M. Artés, P. Gorostiza, J. Veciana, C. Rovira, Nature Chem. 2011, 3, 359.
  • M. Mas-Torrent, C. Rovira, J. Veciana. Adv. Mater., 2013, 25, 462-468
  • C. Simão, M. Mas-Torrent, V. Andre, M.T. Duarte, J. Veciana, C. Rovira, Chem. Sci.2013, 4, 307-310
  • C. Simão, M. Mas-Torrent, J. Casado-Montenegro, F. Otón, J. Veciana, C. Rovira,  J. Am. Chem. Soc. 2011, 133, 3256
  • C. Simão, M. Mas-Torrent, J. Veciana, C. Rovira, Nano Letters, 2011, 11, 4382    
  • J. Casado-Montenegro, M. Mas-Torrent, F. Otón, N. Crivillers, J. Veciana, C Rovira, Chem. Commun. 2013, 49, 8084-8086
  • N. Crivillers, Y. Takano, Y. Matsumoto, J. Casado-Montenegro, M. Mas-Torrent, C. Rovira, T. Akasaka, J. Veciana, Chem. Commun. 2013, 49, 8145-8147
  • E. Marchante, N. Crivillers, M. Buhl, J. Veciana, M. Mas-Torrent, Angew. Chem. Int. Ed. 2015, DOI: 10.1002/anie.201508449

Molecular wires and spintronics

The increasing interest in miniaturizing electronic devices to achieve denser circuits will eventually entail the utilization of molecules as active components. Envisaging this, over the last few years a vast amount of research has been devoted to the investigation of the transport properties of organic molecules. In NANOMOL we are working on this research line both in mixed-valence molecules in solution and also in molecular junctions. A particular case is the exploration of the transport properties through open-shell molecules in which the intrinsic molecular magnetic moment can be exploited to encode information. This research is embedded in the emerging field of spintronics, which is raising great interest for the development of memory storage devices.

spintronics

For relevant recent publications on this topic see:

  • N. Crivillers, M. Paradinas, M. Mas-Torrent, S. T. Bromley, C. Rovira, C. Ocal, J. Veciana, Chem. Commun. 2011, 47, 4664.
  • V. Lloveras, J. Vidal-Gancedo, T.M. Figueira-Duarte, J. F. Nierengarten, J. J. Novoa, F. Mota, N. Ventosa, C. Rovira, J. Veciana, J. Am. Chem. Soc. 2011, 133, 5818.
  • F. Otón, V. Lloveras, M. Mas-Torrent, J. Vidal-Gancedo, J. Veciana, C. Rovira, Angew. Chem. Int. Ed. 2011, 50, 10902-10906.
  • S. Rodriguez-Gonzalez, B. Nieto-Ortega, R.C. Gonzalez-Cano, V. Lloveras, J.J. Novoa, F. Mota, J. Vidal Gancedo, C. Rovira, J. Veciana, V.G. Baonza, J.T. Lopez-Navarrete, J. Casado, J. Chem. Phys. 2014, 140, 16903
  • R. Frisenda, R. Gaudenzi, C. Franco, M. Mas-Torrent, C. Rovira, J. Veciana, I. Alcon, S.T. Bromley, E. Burzurí, H.S.J. van der Zant, Nano Lett. 2015, 15, 3109-3114

Bistable Donor-Acceptor Systems: Towards Molecular Rectifiers

The use of D-A molecules is interesting for its use as building block for active rectifiers in electronic devices. At the same time D-A dyads can lead to bistability (neutral and the zwitterionic states) upon application of an external stimulus (temperature, pressure, electric field, etc) through an Intramolecular Electron Transfer (IET) process opening the way to molecular switches and memories. We study the bistability phenomena in a family of neutral polychlorotriphenylmethyl radical acceptors connected to different donor units (ferrocenes or tetrathiafulvalenes, TTFs) with magnetic, electric and optical properties that can be switched between the two different states. These phenomena take place in solution and in solid state revealing the role of the cooperative intermolecular electrostatic interactions responsible for the bistability.

 donorAcceptor

Interestingly, when using the TTF the IET induced a spontaneous self-assembly of the TTF units which can form intrinsically conducting stacks. In these systems, the interplay between magnetic and conducting properties will be crucial for developing molecule-based spintronic devices.

We are working now on grafting the dyads on conducting surfaces to study the rectification and the influence of an electrical field on the electronic transport.

For relevant representative publications:

  • G. D’Avino, L. Grisanti, J. Guasch, I. Ratera, J. Veciana, A. Painelli, J. Am. Chem. Soc., 2008, 130, 200.
  • J. Guasch, L. Grisanti, V. Lloveras, J. Vidal-Gancedo, M. Souto, D.C. Morales, M. Vilaseca, C. Sissa, A. Painelli, I. Ratera, C. Rovira, J. Veciana, Angew. Chem. Int. Ed. 2012, 51, 11024-11028.
  • J. Guasch, L. Grisanti, M. Souto, V. Lloveras, J. Vidal-Gancedo, I. Ratera, A. Painelli, C. Rovira, J. Veciana, J. Am. Chem. Soc. 2013, 135, 6958-6967.
  • M. Souto, J. Guasch, V. Lloveras, P. Mayorga, J. T. LoĢpez Navarrete, J. Casado, I. Ratera, C. Rovira, A. Painelli, J. Veciana, J. Phys. Chem. Lett. 2013, 4, 2721−272.
  • C. Franco, M. Mas-Torrent, A. Caballero, A. Espinosa, P. Molina, J. Veciana, C. Rovira, Chem. Eur. J., 2015, 21, 5504-5509.
  • M. Souto, M.V. Solano, M. Jensen, D. Bendixen, F. Delchiaro, A. Girlando, A. Painelli, J.O. Jeppesen, C. Rovira, I. Ratera, J. Veciana, Chem. Eur. J., 2015, 21, 8816-8825.
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