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Luminescence and photochemistry of some tervalent chromium complexes.

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Laver, James Leonard (1973) Luminescence and photochemistry of some tervalent chromium complexes. PhD thesis, University of Tasmania.

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Abstract

A number of investigations have been carried out into different
aspects of the luminescence and photochemistry of tervalent chromium
complexes over a temperature range from near liquid helium to room
temperature.
A literature review has been made of previous studies in this
field. From the review it is evident that although the luminescence
properties of many individual complexes have been studied, no systematic examination of the excited state properties of series of complex
salts with different coordinating ligands or different anions has
been made.
In the studies reported here, the relationship between luminescence
and photochemical properties and chemical constitution has
been examined from a number of points of view. Firstly, the
temperature dependence of the emission intensity of a series of
microcrystalline tervalent chromium complexes with oxygen--; nitrogen and
carbon-coordinated ligands has been investigated. The correlation
observed between the degree of temperature dependence. and the nature
of the coordinating ligand has been explained in terms of' differing
positions of the electronic energy levels of the complexes leading to
variation in the rate of non-radiative deactivation of the 2E energy .
level through repopulation of the 4T2 level. Changes in the, temperature
dependence of the luminescence lifetimes of the complexes with different ligands also have been examined and have been found to
parallel those of the emission intensities. This result has been
shown to support the explanation proposed above and to indicate
that when the 4T2 level is thermally accessible from the
2E level,
the thermal repopulation process 2E-4T2 is of major importance
in the non-radiative relaxation of the 2
E level and thus in determining the
emission characteristics of the complexes at room temperature.
Secondly, the result of changes both outside and within the
coordination sphere on the electronic absorption and emission spectra
of trisethylenediamine complexes of chromium has been examined. The
variation in the low temperature emission spectra of the [Cren 3]3+
species with different anions has been studied and the effect of
disubstitution to give- the lower symmetry cis- or trans-bisethylene-
diamine complexes has been investigated through examination of the
reflectance and low temperature emission spectra of these salts. The
emission spectra of the complexes at 7K and the temperature dependence
of the intensity distribution of the emission bands are reported for
the first time. The theory required for the assignment of the spectra
the cis-complexes has. been developed and the assignments of other
authors for the spectra of the trans-complexes have been critically
discussed.
Finally, the effect of variation of the anion on the photochemistry
of the [Cren3]3+
species has been investigated. A systematic study of
the photochemistry of the series in the solid state has been made in
order to resolve current conflicting theories in the literature regarding the decomposition process. The effect of temperature on the photo--
decomposition of the complexes and the likely reaction products have
been discussed and a reaction mechanism involving a thermally unstable
reaction intermediate has been proposed.

Item Type: Thesis (PhD)
Keywords: Chromium compounds, Luminescence, Photochemistry
Copyright Holders: The Author
Copyright Information:

Copyright 1973 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 1973. Bibliography: l. 191-198

Date Deposited: 19 Dec 2014 02:23
Last Modified: 17 May 2017 02:59
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