Molecular nanowires with potential applications from solar energy to quantum information

The small molecule copper phthalocyanine (CuPc) is a well-known industrial pigment used to give blue colours to a range of everyday objects, such as cars or textiles. This molecule is part of a family of polyaromatic molecules which can also behave as semiconductors. These properties have given rise to the exciting field of "molecular electronics", where molecules can be used to replace inorganic semiconductors such as silicon or gallium arsenide to produce flexible, low cost optoelectronic devices.

 In a recent paper published in ACS Nano, a team of researchers from the London Centre for Nanotechnology produced highly directional nanowires of CuPc through a simple sublimation procedure. The wires reach lengths of up to centimetres, and widths as low as 10 nanometers, or 0.000001 centimeters, leading to aspect ratios approaching those of carbon nanotubes. The physical properties of the wires are also novel, with optical absorption through a broader portion of the visible spectrum compared to all previously known forms of CuPc. Such features could be used in organic solar cells, by maximising the efficiency of light absorption, and by promoting the separation of photoexcited states into charges at nanostructured interfaces between electron donors and acceptors.

The team's X-ray and electron microscopy studies also revealed that the molecules adopt a new crystal structure, with maximum electronic overlap along the long axis of the wires, implying highly anisotropic electronic conductivity. Furthermore, the metallic centres of the molecules bear unpaired spins (which can be thought of as small magnets) that interact to form chains where the nearest neighbours alternate between "up" and "down" orientations. The combination of semiconducting and magnetic properties in those flexible quasi one-dimensional objects could therefore also open up applications in "molecular spintronics", by generating new ways to store and transmit information.

 

  SEM image of nanowires with TEM inset

 SEM image of the nanowires. Inset: TEM image of the lattice fringes and schematic of the molecular structure along the long axis of the wire.

 This work has been published in  ACS Nano (H. Wang et al. ACS Nano, 4(7), 3921 (2010)).

Journal link: http://pubs.acs.org/doi/full/10.1021/nn100782w

About the London Centre for Nanotechnology:

The London Centre for Nanotechnology is an interdisciplinary joint enterprise between University College London and Imperial College London. In bringing together world-class infrastructure and leading nanotechnology research activities, the Centre has the critical mass to compete with the best facilities world-wide. Research programmes are aligned to three key areas, namely Planet Care, Healthcare and Information Technology and exploit core competencies in the biomedical, physical and engineering sciences. Website: www.london-nano.com

 About Imperial College London

Consistently rated amongst the world's best universities, Imperial College London is a science-based institution with a reputation for excellence in teaching and research that attracts 13,000 students and 6,000 staff of the highest international quality.

Innovative research at the College explores the interface between science, medicine, engineering and business, delivering practical solutions that improve quality of life and the environment - underpinned by a dynamic enterprise culture.

Since its foundation in 1907, Imperial's contributions to society have included the discovery of penicillin, the development of holography and the foundations of fibre optics. This commitment to the application of research for the benefit of all continues today, with current focuses including interdisciplinary collaborations to improve health in the UK and globally, tackle climate change and develop clean and sustainable sources of energy.

Website: www.imperial.ac.uk

About UCL (University College London)
Founded in 1826, UCL was the first English university established after Oxford and Cambridge, the first to admit students regardless of race, class, religion or gender, and the first to provide systematic teaching of law, architecture and medicine. UCL is the fourth-ranked university in the 2009 THES-QS World University Rankings. UCL alumni include Marie Stopes, Jonathan Dimbleby, Lord Woolf, Alexander Graham Bell, and members of the band Coldplay. UCL currently has over 12,000 undergraduate and 8,000 postgraduate students. Its annual income is over £600 million. www.ucl.ac.uk