Abstract |
The present PhD dissertation describes the synthesis of new porphyrin-based
hybrid molecules and their utilization in light harvesting applications. The
synthesized porphyrin conjugates were modified with functional groups or
connected with other entities depending on their target application.
The first aim of this work was the development of well-organized assemblies
by covalently connecting a molecular self-assembly inducer to a porphyrinoid
chromophore. This approach aims to construct materials with enhanced
properties in the self-assembly state. The resulting hybrids possessed both light
harvesting and self-assembling properties and were further investigated in
applications such as photocatalytic H2 production and photodynamic therapy.
Regarding the self-assembly part, we synthesized and investigated hybrid
chromophore conjugates connected with peptide-based molecules. In detail, we
utilized aromatic and aliphatic dipeptides as well as peptide nucleic acids
(PNAs), bearing various protecting groups, and linked them with porphyrin and
boron-dipyrromethene chromophores. From the synthesized hybrids, those
coupled with a peptide nucleic acid, were applied in photodynamic therapy in
vitro after their self-assembly in spherical nanoparticles.
Concerning the photocatalytic hydrogen (H2) evolution using self-assembled
nanostructures, we covalently attached the diphenylalanine dipeptide to a
tripyridyl porphyrin macrocycle, and the resulting hybrid was able to form selfassembling nanostructures. This hybrid was metallated with non-noble metals,
Zn and Sn, and investigated towards photo-induced H2 production. The Sn
derivative was able to produce hydrogen photocatalytically in the presence of a
cobaloxime catalyst and TEOA as sacrificial electron donor. When the selfassembling nanostructures of the Sn metallated hybrid were employed in the
catalysis, the hydrogen production was improved.
The second target investigated herein concerns the development of artificial
photosynthetic systems based on porphyrin dyads for light driven oxidation
transformations. To that end, several photosensitizer-catalyst dyads were synthesized, characterized and investigated in dye-sensitized photoelectrochemical (DSPEC) devices for water and alcohol oxidation.
For the photocatalytic water oxidation we synthesized a dyad (NiP-Ru)
consisting of a ruthenium tris(bipyridyl), [Ru(bpy)3]2+2+ as photosensitizer, and a
nickel porphyrin, as water oxidation catalyst. Photocatalytic experiments in
organic solutions demonstrated that the covalently connected dyad exhibited
enhanced catalytic activity compared to the non-covalent two-component
system. Moreover, a dye sensitized photoelectrochemical cell (PEC) was
prepared using the NiP-Ru dyad (bearing appropriate anchoring moiety on the
photosensitizer) anchored on TiO2 as photoanode and demonstrated its ability to
perform water oxidation in aqueous media at neutral pH.
Finally, a series of dyads consisted of a zinc porphyrin (ZnP) sensitizer and a
TEMPO organo-catalyst, bearing different anchoring groups on the ZnP, were
synthesized. TiO2 based dye-sensitized photo-electrochemical (DSPEC) systems
were fabricated with these dyads and their catalytic activity in light driven
oxidation of methoxybenzyl alcohol into aldehyde was explored. The
chemisorbed dyads were proved photocatalytically active towards alcohol
oxidation both in aqueous and in organic solutions. The comparison between the
intra-molecular dyad system and the intermolecular two-component system
revealed that both strategies lead to similar performances. However, the employment
dyad is preferable since the recovery of the catalyst is much easier and the quantity
of the catalyst involved is much lower.
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