Research Guides

Department of Chemistry University of Oxford

Professor William Barford

Associate professor of theoretical chemistry

Tutorial fellow in physical chemistry at Balliol College

Physical and Theoretical Chemistry Laboratory, South Parks Road, Oxford, OX1 3QZ.

william.barford@chem.ox.ac.uk

Telephone: +44 (0)1865 275 162

Electronic and Optical Processes in Macromolecular Systems

π-conjugated molecules (e.g., polymers, nanotubes, porphyrins and DNA) occur widely in many biological and synthetic systems; for example, in polymer optoelectronic devices and light harvesting complexes.

These systems are characterised by both strong electron-electron interactions and electron-nuclear coupling. Part of my research is focussed on understanding the effect of these interactions on the electronic and optical properties of conjugated macromolecules. In addition, the roles of disorder and dissipative processes on the loss of electronic phase coherence in macromolecular systems is also being investigated.

Further aims are to predict how the electronic and optical behaviour of condensed phase systems are determined by the multi-scale structures of the component molecules, as well as the inverse problem: how experimental observables coupled with theoretical modelling can help determine multi-scale structures.

These goals are being pursued using a variety of theoretical methods and computational techniques (e.g., DMRG (including time-dependent DMRG) and CI-S) on a wide variety of models (e.g., Pariser-Parr-Pople and Frenkel-Holstein models).

Recent work is listed below under "Selected Publications".

I am a member of the Oxford Theoretical Chemistry Group and the Centre for Doctoral Training in Theory and Modelling in Chemical Sciences (TMCS).

Students interested in Part II projects are welcome to contact me about potential projects. Prospective DPhil students should apply here or to the CDT in TMCS.

My current projects include:
  • Modelling exciton and charge dynamics in conformationally disordered polymers in a dissipative environment. The image below is a three-dimensional plot of exciton wavefunctions, Φ, in the light emitting polymer, poly(p-phenylene). (r is the electron-hole separation and R is the electron-hole centre-of-mass position (in monomer units), see J. Chem. Phys. 129, 164716 (2008).)    
  • Developing theories of optical transitions in pi-conjugated systems. The figure below shows the theoretical emission spectra of PPV as a function of torsonal disorder. The ratio of the 0-0 to 0-1 vibronic transitions is a measure of the average chromophore size, which decreases with increasing disorder (see J. Chem. Phys. 141, 164102 (2014)).
  • Developing the density matrix renormalization group (DMRG) method for quantum chemistry and condensed matter physics.
  • Investigating quantum phase transitions in one-dimensional strongly coupled electron-phonon systems.
My full publication list can be found on the Oxford University Research Archive.
 
Optical Transitions in Conjugated Polymers

Theory of optical transitions in curved chromophores, W. Barford and M. Marcus, J. Chem. Phys. 145, 124111, (2016)

Theory of optical transitions in π-conjugated macrocycles, M. Marcus, J. Coonjobeeharry, and W. Barford, J. Chem. Phys. 144, 154102 (2016)

Theory of optical transitions in conjugated polymers I: Ideal systems, W. Barford and M. Marcus, J. Chem. Phys. 141, 164101 (2014)

Theory of optical transitions in conjugated polymers II: Real systems, M. Marcus, O. R. Tozer, and W. Barford, J. Chem. Phys. 141, 164102 (2014)

Exciton Localization in Disordered Conjugated Polymers

Polarons in π-conjugated polymers: Anderson or Landau?  W. Barford, M. Marcus, and O. R. Tozer, J. Phys. Chem. A 120, 615 (2016)

Local exciton ground states in disordered polymers, D. V. Makhov and W. Barford, Phys. Rev. B 81, 165201 (2010)

Exciton localization in polymers with static disorder, W. Barford and D. Trembath, Phys. Rev. B 80, 165418 (2009)

Exciton Dynamics in Conjugated Polymers

Intrachain exciton dynamics in conjugated polymer chains in solution, O. R. Tozer and W. Barford, J. Chem. Phys. 143, 084102 (2015)

Theory of exciton transfer and diffusion in conjugated polymers, W. Barford and O. R. Tozer, J. Chem. Phys. 141, 164103 (2014)

Exciton dynamics in disordered poly(para-phenylene vinylene) 1: Ultra-fast interconversion and dynamical localization, O. R. Tozer and W. Barford, J. Phys. Chem. A 116, 10310 (2012)

Electronic Processes in Conjugated Polymers

Spin-orbit interactions between inter-chain excitations in conjugated polymers, W. Barford, R. J. Bursill, and D. V. Makhov, Phys. Rev. B 81, 35206 (2010)

Exciton transfer integrals between polymer chains, W. Barford, J. Chem. Phys. 126, 134905 (2007)

Theory of the singlet exciton yield in light emitting polymers, W. Barford, Phys Rev B 70, 205204 (2004)

Excited State Properties of Conjugated Polymers

Excited states in polydiacetylene chains: A density-matrix-renormalization-group study, G. Barcza, W. Barford, F. Gebhard, and O. Legeza, Phys. Rev. B 87, 245116 (2013)

Symmetry-adapted density matrix renormalization group calculations of the primary excited states of poly(p-phenylene vinylene), R. J. Bursill and W. Barford, J. Chem. Phys. 130, 234302 (2009)

Excitons in conjugated polymers: wavefunctions, symmetries and quantum numbers, W. Barford and N. Paiboonvorachat, J. Chem. Phys. 129, 164716 (2008)

Miscellaneous

Localization of large polarons in the disordered Holstein model, O. R. Tozer and W. Barford, Phys. Rev. B 89, 155434 (2014)

Quantized lattice dynamic effects on the Peierls transition of the extended Hubbard model, C. J. Pearson, W. Barford, and R. J. Bursill, Phys. Rev. B 83, 195105 (2011)

Quantized lattice dynamic effects on the spin-Peierls transition, C. J. Pearson, W. Barford, and R. J. Bursill, Phys. Rev. B 82, 144408 (2010)

Review Articles

Perspective: Optical spectroscopy in π-conjugated polymers and how it can be used to

determine multiscale polymer structures, W. Barford and M. Marcus, J. Chem. Phys. 146, 130902, (2017)

Excitons in conjugated polymers: A tale of two particles, W. Barford, J. Phys. Chem. A  117, 2665 (2013)

Book

Electronic and Optical Properties of Conjugated Polymers, W. Barford, Oxford University Press (2013)