Photochemistry
In the early days of the PCL, Ted Bowen made
major contributions to the understanding of photochemical reactions. For
example, work on anthracene and its derivatives showed that whereas oxygen
deactivates the excited singlet state, it reacts only with the triplet state:
dimerization was found to involve reaction of an excited singlet with a ground
state molecule. It could therefore be concluded that molecules in different
electronic states can show differences in reactivity. Another detailed study
was that of fluorescence quenching, where the simple conclusion was reached
that strong quenchers, such as oxygen and sulphur dioxide are effective at
every encounter, both in the gas phase, but also in solution when proper
allowance is made for different fluorescence yields and excited state
lifetimes. Perhaps Bowen's most important work was that on the transfer of
electronic excitation energy between molecules. Anthracene crystals which
contain traces of naphthacene exhibit the green fluorescence of naphthacene
rather than the blue fluorescence of very pure anthracene: It was shown that
this arises by transfer of excitation from the anthracene to the naphthacene,
and such transfer, taking place over distances of many molecular diameters, was
later demonstrated also to occur in solution, in work with Brian Brocklehurst
and Robert Livingstone when the latter was on leave as a Guggenheim Fellow from
the University of Minnesota.
Photochemistry and reaction kinetics have
become increasingly closely interlinked, and at least three groups now in the
PCL have good claims to be called photochemists – Richard Wayne, for his work
on ozone photolysis, Richard Compton and Barry Coles, for their studies of
simultaneous photochemical and electrochemical activation, and Keith
McLauchlan, for his work on the very first stages of photochemically-induced
reactions.
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Double-beam recording
infrared spectrometer in use in the PCL in the 1950s |
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