Mark's research is driven by an interest in the development and properties of optical materials, both molecular and nanostructured. He has interests in the fundamental properties of optical materials and especially the dynamics and properties of excited-states of molecules and carbon nanostructures. Mark's long term goal is the development of new approaches to energy conversion and storage, new display technologies and optical sensing. Our group has expertise in vibrational spectroscopy and especially Raman spectroscopy of various types.
In collaboration with Prof Vikas Berry at Kansas State University we are using Raman spectroscopy to analyse the structures of graphene nanoribbons produced by mechanical fracturing of graphite blocks (produced using the nanotomy process developed by the Berry group). We are investigating if polarised Raman microscopy can be used to analyse the edge type (zig zag or arm-chair) produced by the mechanical fracturing process.
We are interested in using chemical modification of the graphene nanoribbons to control the self-assembly of nanoribbons and molecular materials into functional materials with useful electronic and optical properties. Raman microscopy will be a key technique in the analysis of these self-assembled nanostructures.
We use Raman spectroscopy as a probe of both molecular structure and dynamics. Most recently, we have demonstrated, using resonance Raman spectroscopy, that the excited-state dynamics of phenyl-substituted dipyrrin compounds are controlled by the free rotation of the phenyl substituent. We have also demonstrated that the Raman cross-sections of dipyrrins are amongst the strongest known, making dipyrrins, with their distinct lack of fluorescence ideal candidates as Raman probes.
We have examined the femtosecond (fs) dynamics of Cu(I) bis-phenanthrolines excited-states using a time-domain wavepacket description of resonance Raman intensities. This work follows a number of detailed ultrafast dynamical studies using fluorescence techniques (Tahara et al). The resonance Raman studies provide the missing link between the earliest possible dynamics in the excited-state (i.e. dynamics in the Franck-Condon region) and the femtosecond dynamics probed by ultrafast techniques. Resonance Raman analysis shows that ligand reorganization occurs directly following photoexcitation, which suggests that ligand reorganization must occur either before or at least simultaneously with the well-documented dynamics associated with the change in geometry around the copper metal centre.
We have also used Raman spectroscopy to investigate the structure of room temperature ionic liquids. Ionic liquids have many interesting properties and they have improved the efficiencies of dye-sensitized solar cells. We are interested in the fundamental properties of RTILs as solvents and how they relax around molecular excited-states. We are currently using resonance Raman intensity analysis to develop a semi-quantitative scale of solvent reorganization energies for RTILs analogous to scales of polarity as developed by Reichardt and others.