Spectroscopic and computational techniques for the analysis of photochemically driven reactions

A variety of spectroscopic techniques are employed for the analysis of chemical interactions instigated by photonic excitation. Steady state absorption and emission spectroscopy is useful for characterising photostable compounds and performing constitutional analysis of samples pre and post reaction, but often cannot provide information on reaction intermediates, excited states or reaction dynamics. To address these areas, transient spectroscopic techniques can be used, involving pump - probe measurements to induce a photochemical or photophysical process and monitor it as a fun ction of wavelength and time. In this work, both steady state and tran sient spectroscopic techniques were used to interrogate and characterise a number of novel photoactive species, supported throughout by computational chemistry approaches . Firstly, this includes a number of novel Ir III complexes , synthesised by the Pope group at Cardiff University. These complexes , which largely contain quinoxaline derivatives, display highly tuneable photophysical properties with respect to subtle ligand variation . This tuneability was analysed, both experimentally and computationally, with respect to ligand structure and, using this ligand library set, tuning properties of similar ligands are predicted. Secondly, similar techniques were employed to analyse the photoreduc tion of a photosensitive compound, 2,3,5 - triphenyltetrazolium, and three similar chemical variants , supplied by the Fallis group at Cardiff University. T etrazolium compounds are useful as chemical indicators : their reduction reaction is associated with a colour change, and as such it would be advantageous to inhibit the photochemical reduction to prevent false positives in the chemical reduction process . Through chemical variation of the tetrazolium the photo reaction can be inhibited, and through spectroscopic analysis of this reaction new photochemical pathways are proposed. Finally, initial steps in the d evelopment of a gas phase multi - pass absorption spectrometer for the analysis of trace chem ical intermedi ate species have been undertaken