Synthesis and investigations of novel alkenylporphyrins and bis(porphyrins)
Locos, Oliver Brett (2006) Synthesis and investigations of novel alkenylporphyrins and bis(porphyrins). .
Twelve porphyrin dyads linked by an ethene bridge were synthesised as model
systems for conjugated polymers. The extent of interporphyrin interaction was
investigated for meso-meso and meso-β linked homo- and heterobimetallo-porphyrin
dyads. To complement these dyads, model monomers with alkenyl substituents were
also studied. Once the synthesis of these compounds was achieved, the extent of
interaction was studied using UV-visible and fluorescence spectroscopy and
In order to gain a true indication of the extent of interaction in a dyad, the effect of
the bridge as a substituent must be accounted for. This was achieved by studying the
series of monomers by UV-visible and fluorescence spectroscopy. The increased
conjugation resulting from mono- and bis-alkenyl substituents results in a red shift of
the origin of transition energies in the absorption spectrum which is accompanied by
a broadened and less intense Soret band and an increase in the intensity of the Q
bands. The emission of these compounds also displays an increase in Stokes shift and
a loss of vibronic coupling due to the increased conjugation.
The serendipitous synthesis of three asymmetric meso-β ethene-linked porphyrin
dyads was achieved by the use of palladium-catalysed Heck coupling of mesoethenyl-
with meso-bromoporphyrins. A possible mechanism for this meso to β
rearrangement was proposed. A series of nine meso-meso ethene-linked dyads was
synthesised by palladium-catalysed Suzuki coupling of meso-(2-iodoethenyl)- with
meso-borolanylporphyrins. All of these dyads were characterised by 1D and 2D
NMR as well as MS analysis. The absorption spectra of ethene-linked dyads exhibit
a split Soret band and a red-shifted and intensified HOMO-LUMO band. In the
meso-β dyads, the degree of splitting in the Soret band is sufficient only to generate a
shoulder on the red edge, whereas in the meso-meso dyads two separate bands
appear. The extent of splitting is believed to be an indication of the amount of
The fluorescence profiles of the dyads change dramatically depending upon the
central substituents in the porphyrins and the wavelength used for irradiation, which suggests that different conformations of these compounds give rise to different parts
of their absorption and emission profiles. The fluorescence profiles of the dyads also
do not reflect their absorption profiles, and therefore the excitation of the dyad is
believed to be accompanied also by a change in geometry. All ethene-linked dyads
exhibited an anti-Stokes shift, and the excitation spectra of the different parts of the
fluorescence envelope also support the possibility of different conformers
contributing to the fluorescence spectra.
Molecular mechanics and time-dependent quantum mechanical calculations were
performed on seven ethene-linked porphyrin dyads. These calculations further
support the proposal of different conformations contributing to the physical
properties of ethene-linked dyads. Electronic structure calculations also show
considerable electron density on the alkene for the meso-meso ethene-linked dyads,
which highlights the important influence of this bridge upon the electronic nature of
these conjugated diporphyrins.
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|Item Type:||QUT Thesis (PhD)|
|Supervisor:||Arnold, Dennis& Bottle, Steven|
|Keywords:||novel alkenylporphyrins, bis-porphyrins, porphyrin dyads, ethene bridge, conjugated polymers|
|Divisions:||Past > QUT Faculties & Divisions > Faculty of Science and Technology|
Past > Schools > School of Physical & Chemical Sciences
|Department:||Faculty of Science|
|Institution:||Queensland University of Technology|
|Copyright Owner:||Copyright Oliver Brett Locos|
|Deposited On:||03 Dec 2008 14:02|
|Last Modified:||29 Oct 2011 05:47|
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