Introduction to the special issue dedicated to David Phillips

This issue of Photochemical & Photobiological Sciences is published in honour of the contribution David Phillips has made to science and the scientific community. The contributed papers are by his colleagues who have had, and continue to have, the privilege to work with him.

David's scientific interest has crossed many boundaries and it can be said that through his scientific leadership he has taken chemistry right into the heart of medical science. He has made a very significant contribution to chemistry, publishing more than 400 research papers, as well as numerous reviews, book chapters and textbooks, some 570 publications in all.

David Phillips was awarded his PhD in physical chemistry in 1964 at the University of Birmingham, UK. His area of study was in reactions of free radicals generated photochemically.

David has always enjoyed the great opportunities offered by science to travel abroad and work within the international science arena. After completing his PhD his first academic journey, funded by a Fulbright Fellowship, took him to the University of Texas at Austin where he carried out a postdoctoral fellowship with W. Albert Noyes Jr. (1964–1966). Following this he moved on as a Royal Society/Academy of Sciences of USSR Exchange Fellow to the Institute of Chemical Physics, Moscow, USSR during 1966–1967.

Upon his return to the UK he secured an academic position within the Chemistry Department at the University of Southampton where he stayed from 1967–1979. He then moved to London taking up the post as Wolfson Professor of Natural Philosophy and Deputy Director of the Royal Institution of Great Britain, London, at the time when Lord Porter, then Sir George Porter, was Director. The Royal Institution provided David with the opportunity to promote the public understanding of science, for both young and old. David delivered the series of Royal Institution Christmas Lectures (jointly with J. M. Thomas) on BBC television in 1986–1987. He developed his demonstration lectures and continues to give several of these across the world annually. It is befitting that he was awarded the RSC Nyholm Medal in 1994, the BD Shaw Medal in 2005, the Michael Faraday award of the Royal Society, London, for public understanding of science, and OBE, Birthday Honours, June 1999 for his services to science education.

In 1989 the Royal Institution was a changing place and this was when David took one of the toughest decision in his career, to leave the RI and move to Imperial College, London, as Professor of Physical Chemistry. He became Head of Department from 1992 and maintained this role until 2002 and with his strong leadership IC Chemistry secured the position as one of the top Chemistry Departments in the UK and in the world. In 1994 David was awarded The Nyholm Lectureship and Medal. From 2002 David became Hofmann Professor of Chemistry, and Dean of the Faculties of Life Sciences and Physical Sciences. David continues to work at Imperial College as Emeritus Professor of Chemistry and Senior Science Ambassador for Schools at Imperial College, the latter again reflecting his commitment to inspiring the next generation of scientists. David was Chairman of the European Photochemistry Association from 2004 to July 2007.

Gas phase spectroscopy

David's early interest in gas phase spectroscopy and photochemistry led him to be amongst the first to adopt the technique of supersonic jet spectroscopy, in which molecules are cooled to extremely low rotational and vibrational temperatures in a supersonic expansion. Under these conditions, the absorption spectra of polyatomic molecules become highly simplified, permitting the use of high resolution laser-induced fluorescence to provide detailed structural information. The main focus of this work was to understand the effect of solvation of fluorophores in isolation by producing sequentially solvated ground state van der Waals and hydrogen bonded complexes, prompting the quip from Ed Schlag that he had joined the ‘Solvation Army’. One of his key contributions in this area was the study of van der Waals complexes of aromatic molecules and solvent, allowing the investigation of solute–solvent interactions, particularly hydrogen bonding interactions, at the molecular level.¹ Later work was on spectroscopy and dynamics of molecules with groups exhibiting large amplitude low frequency vibrations. This method was used to elucidate the photophysical properties of molecules that exhibit ‘dual fluorescence’, such as the well known TICT states of 4-aminobenzonitriles.² He only reluctantly gave up these fascinating fundamental studies when an unrealistic multi million pound refit of equipment was necessary.

Photodynamic therapy

David then went onto pioneering developments in time-resolved spectroscopy that he could apply to characterise the photochemistry of sensitizers used in the photodynamic treatment of cancer (PDT). David is widely regarded as one of the world leading experts in the field of PDT. His interest in this stems for work carried out in the early 1980s, when he began studies on the use of sulfonated aluminium phthalocyanines as photoactivated bleaching agents.³ In subsequent years he established collaborations with biologists and medics, and embarked upon a detailed investigation into the photophysics and photochemical properties of phthalocyanines as PDT sensitizers. He has over 40 publications in this area representing his contribution which demonstrates how his efforts have screened potential drugs from test-tube to cells and onto clinical trials.⁴ David has carried out detailed investigations into the properties of these materials under model biological conditions, demonstrated their efficacy as photodynamic agents for in vitro and in vivo measurements and developed imaging techniques for the study of sensitiser localisation both on the single cell level and tissue.⁵ More recently he was one of the founders of a spin-out company, Photobiotics, which aims to bring photodynamic treatment and technology to market.

Time-resolved fluorescence and single photon counting

David is also recognised as a leading figure in the field of time-resolved fluorescence measurements,⁶ having co-authored what is considered by many to be the definitive textbook ‘Time-Correlated Single Photon Counting’.⁷ This text, which spans the underlying principles, technical details and data analysis software, is very highly cited; currently over 1400 times. His early publications describe his pioneering work using mode-locked ion lasers⁸ and applications of time-resolved fluorescence for the study of polymer dynamics.⁹ His most recent work in this area is in two-photon fluorescence lifetime imaging, demonstrating his sustained and continuous contribution to the field. David and co-authors have also used advanced lifetime imaging techniques to get insight into the function of PDT sensitizers inside living cells.¹⁰

Time-resolved resonance Raman spectroscopy

David has also supported the development of UK National Facilities and played a major role from the mid 1980s to the present day in the development of time-resolved resonance Raman spectroscopy.¹¹ His early work was in the nanosecond time regime investigating the fundamentals of electron transfer between excited state acceptors and donors in the solution phase.¹² Always at the cutting edge of available technology he moved into the picosecond domain in the early 1990s, investigating the early relaxation dynamics of electronic excited states of complex molecules.¹³ Using this apparatus he returned to investigating the intramolecular charge transfer reaction of 4-dimethylaminobenzonitrile (DMABN),¹⁴ finding some evidence, to controversially support the twisted nature of the charge transfer state. As well as applying Raman spectroscopy to study DMABN he also applied the complementary technique of ultrafast time-resolved infrared spectroscopy, where he made the first observation of the hydrogen bond formation in protic solvents to charge transfer states, the so called HICT state.¹⁵David is one of the ‘good guys’ in science and has always been able to provide young researchers with an environment where they could nurture their own ideas. His efforts have been extremely successful fostering 54 PhD students and more than 40 post-doctoral fellows, totalling some 300 years of research (excluding his own 46 to date!). Many-many members of the ‘Phillips Group’ have gone on to become senior academics in their own right continuing his leading work in photochemical and photobiological science.

Anthony W. Parker, Anita Jones and Andy Beeby

Selected bibliography
1	A. R. Auty, A. C. Jones and D. Phillips, Fluorescence excitation spectra and decay times of jet-cooled dibenzofuran and the dibenzofuran–water complex, Chem. Phys. Lett. 1984, 112, 529–33; H. Yu, S. M. Zain, I. V. Eigenbrot and D. Phillips, Investigation of carbazole derivatives and their van der Waals complexes in the jet by laser-induced fluorescence, J. Photochem. Photobiol., A, 1994, 80, 7–16; E. M. Gibson, A. C. Jones, A. G. Taylor, W. G. Bouman, D. Phillips and J. Sandell, Laser-Induced Fluorescence Spectroscopy of 4-Aminobenzonitrile, 4-(N,N-dimethylamino)benzonitrile, and their van der Waals Complexes in a Supersonic Jet, J. Phys. Chem. 1998, 92, 5449–5455.
2	H. Yu, E. Joslin, B. Crystall, T. Smith, W. Sinclair and D. Phillips, Spectroscopy and dynamics of jet-cooled 4-aminobenzonitrile (4-ABN), J. Phys Chem., 1993, 8146–51, R. Howell, D. Phillips, H. Petek and K. Yoshihara, Fluorescence of jet-cooled dimethylaminobenzontrile, its aggregates and solvated complexes, Chem. Phys., 1994, 188, 303–16; R. Howell, A. G. Taylor, A. C. Jones and D. Phillips, Laser-induced Fluorescence of Dimethylaminobenzoic Esters in Solution and Supersonic Jet, Chem. Phys. Lett., 1989, 163, 282–90; D. Phillips, Studies on torsional motion in aromatic amines, J. Photochem. Photobiol., A, 1997, 105, 307–15.
3	J. R. Darwent, I. McCubin and D. Phillips, Excited singlet and triplet state electron-transfer reactions of aluminium(III) sulfonated phthalocyanine, J. Chem. Soc., Faraday Trans. 2, 1982, 78, 347–357.
4	D. Phillips, Chemical mechanisms in photodynamic therapy with phthalocyanines, Prog. React. Kinetic. Mech., 1997, 22, 175–300.
5	J. A. Lacey and D. Phillips, The photosensitisation of Escherichia coli using disulfonated aluminium phthalocyanine, J. Photochem. Photobiol., A, 2001, 142, 145–150.
6	S. R. Meech and D. Phillips, Photophysics of Some Common Fluorescence Standards, J. Photochem., 1983, 23, 193–217.
7	D. V. O'Connor and D. Phillips, Time-Correlated Single Photon Counting, Academic Press, London, 1984.
8	K. P. Ghiggino, A. J. Roberts and D. Phillips, Time-resolved Fluorescence Spectroscopy Using Pulsed Lasers, J. Phys. E: Sci. Instrum., 1980, 13, 446–450.
9	W. J. Feast, I. S. Millichamp, R. H. Friend, M. E. Horton, D. Phillips, S. D. D. V. Rughooputh and G. Rumbles, Optical-Absorption and Luminescence in Poly(4,4'-Diphenylenediphenylvinylene), Synth. Metals, 1985, 10, 181–191.
10	K. Suhling, P. M. W. French and D. Phillips, Time-resolved fluorescence microscopy, Photochem. Photobiol. Sci., 2005, 4, 13–22.
11	J. N. Moore, D. Phillips and R. E. Hester, Time-resolved Resonance Raman-Spectroscopy Applied to the Photochemistry of the Sulfonated Derivatives of 9,10-Anthraquinone, J. Phys. Chem., 1988, 92, 5619–5627.
12	E. Vauthey, A. W. Parker, B. Nohova and D. Phillips, Time-resolved Resonance Raman-Study of the Rate of Separation of a Geminate Ion-Pair Into Free Ions in a Medium Polarity Solvent, J. Am. Chem. Soc., 1994, 116, 9182–9186.
13	G. D. Scholes, P. Matousek, A. W. Parker, D. Phillips and M. Towrie, Inner sphere reorganization dynamics accompanying charge transfer in cyanoterphenyl, J. Phys. Chem. A, 1998, 102, 1431–1437.
14	W. M. Kwok, C. Ma, P. Matousek, A. W. Parker, D. Phillips, W. T. Toner and M. Towrie, A determination of the structure of the intramolecular charge transfer state of 4 dimethylaminobenzonitrile (DMABN) by Time-resolved Resonance Raman Spectroscopy, J. Phys. Chem. A, 2001, 105, 984–990.
15	W. M. Kwok, M. George, D. C. Grills, C. S. Ma, P. Matousek, A. W. Parker, D. Phillips W. T. Toner and M. Towrie, Direct observation of a hydrogen-bonded charge-transfer state of 4-dimethylaminobenzonitrile in methanol by time-resolved IR spectroscopy, Angew. Chem., Int. Ed., 2003, 42, 1826–1830.

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