Our Research

Photochemistry at Insulator Surfaces

Photochemistry at insulator surfaces necessarily involves the study of reactions occuring in opaque and often heterogeneous environments. In order to study such reactions, the technique of Diffuse Reflectance Laser Flash Photolysis has been developed, where changes in the intensity of diffusely reflected rather than transmitted light following laser excitation serves as the analytical parameter. These changes are then analysed using Kubelka-Munk theory in order to obtain transient concentration changes. Various models are used to characterise the data obtained, including fractal-dimensional and dispersive kinetics. Monte-Carlo simulations are underway to provide the link between fitted parameters and physical variables.

Research at Loughborough into photochemistry at insulator surfaces focusses primarily on the photochemistry and photophysics of molecules adsorbed to the surface of silica gel. In particular, diffusional reactions on silica have been probed using triplet-triplet annihilation reactions of anthracene, and using electron transfer from aromatic tertiary amines to the anthracene radical cation. An example of the data which can be obtained is shown in figure 1 below. Here N,N,N',N'-tetramethyl-1,4-phenylenediamine (TMPD) acts as an electron donor to the anthracene radical cation formed by multiphoton ionisation using 355nm excitation. In this case, decay of the anthracene radical cation is accompanied by formation of the TMPD radical cation with characteristic absorption peaks at 560nm and 610nm

Figure 1: N,N,N',N'-tetramethyl-1,4-phenylenediamine coadsorbed with anthracene on silica gel

Selected References

Worrall, D.R., Kirkpatrick, I. and Williams, S.L. “Bimolecular processes on silica gel surfaces: Energetic factors in determining electron transfer rates” Photochemical and Photobiological Sciences 3, 2004, 63-70

 Worrall, D.R.; Williams, S.L.; Eremenko, A.; Smirnova, N.; Yakimenko, O. and Starukh, G. “Laser flash photolysis study of electron transfer processes of adsorbed anthracene on photocatalytic titania-silica surfaces” Colloids and Surfaces A: Physicochemical Aspects 230(1-3), 2004, 45-55

Worrall, D.R.; Kirkpatrick, I. and Williams, S.L. “Controlling factors in electron and energy transfer reactions on silica gel surfaces” Photochemical and Photobiological Sciences 1, 2002, 896-901

Worrall, D.R., Williams, S.L., Wilkinson, F., Crossley, J.E., Bouas-Laurent, H. and Desvergne, J.P.,''Spectroscopy and Ion-Electron Recombination Kinetics of Radical Ions of Anthracenes and Substituted Anilines on Silica Gel'', Journal of Physical Chemistry B, 103(43), 1999, pp 9255-9261.

Worrall, D.R., Williams, S.L. and Wilkinson, F.,''Electron Transfer Reactions of Anthracene Adsorbed on Silica Gel'', The Journal of Physical Chemistry B, 101(24), 1997,  pp 4709-4716.

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