Bimolecular rate constants for the quenching of up to 15 excited
triplet aromatic hydrocarbons by eight S-diketonate complexes of Cr(III)
and four of Co(III) have been obtained using nanosecond laser flash
The bimolecular rate constants have been plotted against donor energy
and for those quenchers whose rate constants follow the available
spectroscopic energy levels in the quencher, electronic energy transfer is
established to be the mechanism of quenching. As the electrochemical
reduction potential of the quencher is reduced by the introduction of
trifluoromethyl groups into the S-diketonate complexes, an increase in
quenching efficiency is observed which may be explained by modifying the
mechanism of quenching to include electron transfer. Theoretical models
have been developed in order to predict quenching constants for the
different mechanistic pathways.
For the quenching of excited triplet states by y-substituted chromium
(III) complexes, rate constants greater than those predicted by the Debye
Equation, once spin statistics have been introduced, were obtained.
Diffusion theories were examined and a Spernol-Wirtz type treatment was
employed,since this takes into account microfiction between solute and
solvent molecules of differing molecular radii. Using this diffusion
theory allowed all of the results presented to be interpreted within
the framework of the theoretical models.
The effect of geometrical isomerism on the quenching efficency of a
chromium(III) complex was investigated and it was found that the aisisomers
is a more efficient electronic energy transfer quencher than the
trans form, especially when energy is being accepted by the quartet state.
The general nature of the approach developed in the thesis was
examined by measuring the quenching rate constants for four Co(III)
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.