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Prof. Anthony Harriman
Professor of Physical Chemistry and Co-Director of the Molecular Photonics Laboratory

The Molecular Photonics Laboratory is a research organisation concerned with the design, synthesis and photophysical examination of multi-component molecular systems. The Laboratory is funded, in part, by EPSRC. Further details can be found at: www.ncl.ac.uk/mpl/

Research Interests

Four main areas of research are being pursued: (1) The effect of molecular conformation on the rate of through-bond electron transfer is being studied with reference to tailor-made donor-connector-acceptor systems. In particular, the torsion angle between phenylene rings in a bridging biphenylene unit has been varied systematically by means of a strap that constrains the geometry. A total of 14 separate compounds has been prepared and the effect of angle is being examined for electron delocalisation at the triplet level, intervalence charge transfer between redox-active terminals and electron exchange between photoactive terminals. The results should lead to a better understanding of electronic coupling in conjugated molecules. At present, there are no reliable experimental data relating to how the torsion angle affects the degree of electronic coupling between remote terminals.

(2) Molecules capable of unusually long-range (e.g., >20 nm) triplet energy transfer are being designed. These molecular triads have bridging naphthalene units that function as relays for energy transfer between the terminals. Intramolecular energy transfer involves a Monte Carlo random walk of photons along the naphthalene-like connector before being trapped at the acceptor. Understanding the kinetics requires a new analytical approach. The work has obvious relevance to light-emitting polymeric diodes. The basic idea is to develop new prototypes for use in molecular photonic devices and to examine, in detail, photon hopping mechanisms. The latter are of importance in UV-damaged DNA.

(3) The availability of ultrafast laser spectroscopic tools allows the direct involvement of upper-lying excited states in energy- and/or electron-transfer processes. With appropriately designed molecules, it should be possible to change the direct of electron transfer by excitation into different excited states localised on the same chromophore. This possibility is being examined with respect to porphyrin-ruthenium(II) bis(terpyridine) dyads equipped with secondary electron acceptors. Excitation into the first singlet state of the porphyrin directs the electron to an attached quinone. However, illumination into the second singlet state is followed by rapid energy transfer to the metal complex. This is followed by electron transfer to a remote quinone. The detailed mechanism is now being examined. Related work is exploring the electron-transfer steps that follow from illumination of donor-acceptor dyads equipped with multiple bridges. The intention is to better understand the superexchange mechanism and to construct new systems displaying very long-lived charge-separated states.

(4) We are using modern quantum chemistry to calculate the rates of electron transfer in donor-connector-acceptor molecules from first principles. It is now possible to compute reliable estimates for the nuclear and solvent reorganisation energies whilst molecular dynamics simulations allow calculation of the overall thermodynamic driving force. Several new methods have been developed that allow computation of the electronic coupling matrix element. The robustness and versatility of these latter methods are now been examined. In several cases, however, it has been possible to compute rates of through-space and through-bond electron transfer that are close to the experimental value. The long-term goal of this work is to develop a kind of combinatorial approach to molecular electronics. Here, quantum chemistry will be used to identify appropriate components and to help design suitable prototypes prior to expensive synthesis.

Equipment includes: 2 fluorescence spectrometers; 2 UV-visible spectrophotometers; a time-resolved fluorescence spectrometer; 2 optical cryostats (one for 77 K and one going down to 2 K); a Stark-effect spectrometer; very high-pressure absorption and emission facilities; 2 Silicon Graphics work stations; 19 PC’s; a laser flash photolysis set for ps studies; a cyclic voltammetry set up with spectroelectrochemical capabilities; gel electrophoresis; a wide range of software for quantum chemical calculations (including INSIGHT-2, CACHE, Q-CHEM; GAUSSIAN-03, AMPAC and CHARMM); a fluorescence microscope; a time-resolved luminescence spectrometer for the near-IR region; and a large collection of data analysis software. Additional equipment is under construction. Funding has been requested from EPSRC to allow construction of a further laser flash spectrometer, having both optical and resonance Raman capabilities. Plans are at an advanced stage to build a fluorescence correlation spectrometer.

Other Expertise

solar energy conversion
artificial photosynthesis
quantum chemistry
inorganic photochemistry
molecular photophysics

Current Work

[300] Harriman, A.; Khatyr, A.; Ziessel, R. “The photophysical properties of short, linear arrays of ruthenium(II) tris(2,2’-bipyridine) complexes”, Res. Chem. Intermed., in press.
[301] Benniston, A. C.; Harriman, A.; Lawrie, D. J.; Rostron, S. A. “A closely-coupled pyrene dimer having unusually intense fluorescence” Eur. J. Org. Chem., 2004, 2272.
[302] Harriman, A. “Unusually slow charge recombination in molecular dyads” Angew. Chem., Int. Ed., 2004, 43, 4985.
[303] Benniston, A. C.; Harriman, A.; Li, P.; Sams, C. A.; Ward, M. D. “Orientational control of electronic coupling in mixed-valence, binuclear ruthenium(II)-bis(2,2’:6’,2”-terpyridine) complexes” J. Am. Chem. Soc., 2004, 126, 13630.
[304] Benniston, A. C.; Chapman, G. M.; Harriman, A.; Mehrabi, M. “Intramolecular energy transfer in molecular dyads comprising free-base porphyrin and ruthenium(II) bis(2,2’:6’,2”-terpyridine) termini” J. Phys. Chem. A, 2004, 108, 9026.
[305] Harriman, A.; Mehrabi, M.; Maiya, B. G. “Light-induced electron transfer in porphyrin-calixarene conjugates” Photochem. Photobiol. Sci., 2005, 4, 47.
[306] Benniston, A. C.; Harriman, A.; Li, P.; Sams, C. A. “Temperature-induced switching of the mechanism for intramolecular energy transfer in a 2,2’:6’,2”-terpyridine-based Ru(II)-Os(II) trinuclear array” J. Am. Chem. Soc., in press.
[307] Benniston, A. C.; Harriman, A.; Li, P.; Sams, C. A. “Comparison of the photophysical properties of osmium(II) bis(2,2’:6’,2”-terpyridine) and the corresponding ethynylated derivative” J. Phys. Chem. A, in press.
[308] Harriman, A.; Ziessel, R. “Electronic conduction in photoactive metallo-wires” In Carbon-rich Compounds: Molecules to Materials, Wiley-VCH, submitted.
[309] Harriman, A.; Mayeux, A.; Stroh, C.; Ziessel, R. “Photophysical properties of binuclear ruthenium(II) bis(2,2’:6’,2”-terpyridine) complexes built around a central 2,2’-bipyrimidine receptor” Inorg. Chem., submitted.
[310] Verhoeven, J. W.; van Ramesdonk, H. J.; Groeneveld, M. M.; Benniston, A. C.; Harriman, A. “Long-lived charge-transfer states in compact donor-acceptor dyads” Chem. Phys. Chem., in press.
[311] Benniston, A. C.; Harriman, A.; Li, P.; Rostron, J. P.; Verhoeven, J. W. “Illumination of 9-mesityl-10-methylacridinium ion does not produce an exceptionally long-lived photoredox state” Chem. Commun., submitted.
[312] Benniston, A. C.; Chapman, G. M.; Harriman, A.; Rostron, S. A. “Reversible luminescence switching in a ruthenium(II) bis(2,2’:6’,2”-terpyridine)-benzoquinone dyad” Inorg. Chem., in press.
[312] Verhoeven, J. W.; van Ramesdonk, H. J.; Zhang, H.; Groeneveld, M. M.; Benniston, A. C.; Harriman, A. “Long-lived charge-transfer states in 9-aryl-acridinium ions: Fact and fiction” Inter. J. Photoener., in press.
[313] Harriman, A.; Khatyr, A.; Rostron, S. A.; Ziessel, R. “Light-induced charge transfer in metal-based molecular-scale wires” Metal-containing and metallo-supramolecular polymers and materials. ACS Symposium Series, 2005, in press.
[314] Benniston, A. C.; Harriman, A.; Lawrie, D. J.; Mehrabi, M. “Sensing properties of an artificial biological probe: DNA binding of a molecular-scale receptor in the presence of zinc(II) ions” Eur. J. Org. Chem., 2005, in press.
[315] Harriman, A. “Artificial Photosynthesis: Static and dynamic electron-transfer processes between a porphyrin and benzo-1,4-quinone” Imperial College Press, London, 2005.

Research Roles

All my research work is now directed through the Molecular Photonics Laboratory; see the dedicated web site for further details. www.ncl.ac.uk/mpl/

Postgraduate Supervision

My research group forms the basis of the Molecular Photonics Laboratory. Currently, there are 4 final year students (Sarah Mitchell, James Rostron and Sarah Rostron) 3 intermediate students (Ben Allen, Erantzu Llarena, Consuelo Pariani) and one first year student (Laura Mallon). Several PDRA’s also work in the group (Peiyi Li, Craig Sams, Songjie Yang, Sarah Howell, Guillaume Izzet, Chunfang Yu, and Yongang Zhi). Funding is provided by way of EPSRC and Leverhulme and a grant from the Procter & Gamble Company.

Funding

EPSRC Grant Reference: EP/D001994/1
Delayed Fluorescence as a New Form of Molecular Imaging £85,402
EPSRC Grant Reference: EP/D032946/1
Directed Electron Transfer £327,903
EPSRC Grant Reference: GR/P02066/01
Ind. CASE - University of Newcastle upon Tyne £121,350
EPSRC Grant Reference: GR/S00088/01
Very long-range electron exchange in donor-connector-acceptor triads
£301,531
EPSRC Grant Reference: GR/N26869/01
MTP: DESIGNING CHEMICAL SOLUTIONS £200,861
EPSRC Grant Reference: GR/R23305/01
Controlling Through-Bond Electronic Coupling Via Orientation Effects
£266,435
EPSRC Grant Reference: GR/R79579/01
Light Years Ahead: Photochemistry enters the public arena £20,338
EPSRC Grant Reference: GR/R92615/01
ROPA: Promoting directional electron transfer via selective illumination into upper and lower excited states £113,266

Patents

A total of 11 patents have been awarded, covering many areas of our applied photochemistry work.

Background

Professor Harriman owns a large house in the South of France, just outside St. Tropez, in the centre of the Provencal wine-producing region. The house is set in grounds covering 5 acres, with an orchard, small vineyard and swimming pool. He has worked in universities in the United Kingdom, France and the United States. He has given research lectures in 28 different countries around the globe and has enjoyed extended trips to Japan, Australia and South Africa. He collaborates on research projects with scientists around the world and has written more than 340 scientific articles.

Roles and Responsibilities

Teaching contemporary physical chemistry presents a tremendous challenge in that most students are afraid of the mathematical component. An important objective for the near future, therefore, is to introduce computer-assisted teaching - where graphical methods are used in place of numerical ones - and to teach those special mathematical skills of direct relevance to chemistry. A longer-term goal is to devise an individual electronic tutor for each student.

Qualifications

PhD
Grad RIC
HNC
ONC

Previous Positions

Director of the Center for Fast Kinetics Research at the University of Texas at Austin, Autin, Texas, USA 1988-95
Assistant Director of the Royal Institution of Great Britain (London, UK)1978-88
Professor of Chemistry at the University of Strasbourg, Strasbourg, France 1995-99

Memberships

Marseilles football supporters club
Royal Society of Chemistry

Honours and Awards

Sir James Dewar Research Fellowship 1977
Royal Society (London) Visiting Research Scholarship 1982
Corday-Morgan Medal (RSC) 1984
Le Prix Grammaticakis-Neumann en Photochimie 1985

Languages

English, French

Undergraduate Teaching

CHY101 ... General Chemistry : covers the basic concepts of concentrations, solutions, colligative properties, chemical equilibria, pH, buffers, hydrolysis, solubility product and rate expressions.

CHY120 … Elements of Physical Chemistry - Spectroscopy : covers the fundamentals of spectroscopy, including mass spectra, atomic spectra, UV-visible absorption and emission spectroscopy, vibrational and rotational spectroscopy, Mössbauer, NMR and EPR spectroscopy.

CHY220 … Intermediate Physical Chemistry - Quantum mechanics.

CHY320 … Advanced Physical Chemistry - Energetics and Dynamics : describes how molecules dissipate excess energy, the mechanisms of molecular diffusion and migration, activated complex theory, potential energy surfaces and molecular energy transfer.

CHY425 … Chemical Sensors - Luminescence : introduces the newly-emerging technique whereby luminescence spectroscopy, combined with advanced synthesis, provides ultrasensitive and highly specific protocols for recognition and quantitative analysis of solutes, even at the single molecule level.

Postgraduate Teaching

The chemical sensors module is repeated at MSc level. This course isavailable for distance learning.