| Abstract |
Throughout the years, CO2 has played a crucial role both in the development and shaping
evolutionary changes in terrestrial ecosystems. However, in recent years a concerning
increase of the total amounts of emitted CO2 in the atmosphere was detected. Based on this
observation, scientists are now drawing attention to imminent climate changes that may
disrupt the ecosystem balance, hence endangering life on the planet. Consequently, the
development of innovative and efficient systems, which are able to capture and utilize CO2, is
necessary towards the reduction of the CO2 atmospheric levels. Photocatalytic conversion of
CO2 into useful products such as hydrocarbons and oxygenates is the most promising method
mainly due to the clean and sustainable nature of solar energy. What is more, the products of
the CO2 reduction can be utilized instead of conventional energy sources. To date, numerous
molecular photocatalytic systems have been developed in order to reduce CO2 into products
such as CO, HCOOH, CH 4 etc. These systems consist of a photosensitizer which absorbs
solar energy (PS), a CO 2 reducing catalyst (Cat) and a sacrificial electron donor (SED). The
overall efficiency of such systems depends both on the physicochemical and electrochemical
properties of the three major components (Ps, Cat, SED) and their synergistic action. During
the past years, the scientific interest has been mainly focused on the synthesis and study of
supramolecular systems that consist of a PS covalently linked to a Cat. This approach leads to
a more efficient electron or/and energy transfer from the PS to the Cat, thus improving the
photocatalytic activity of these systems. The aim of this master thesis was the synthesis of
two new supramolecular assemblies Cat-PS and their study in photocatalytic CO2 reduction
systems. An iron (III) porphyrin was selected as the catalyst while a tris-bipyridine Ru (II)
complex played the role of the photosensitizer. The phenyl groups of the iron porphyrin (Cat)
macrocycle were functionalized with –OMe groups in ortho positions. The two synthesized
dyads (FeDyad 1 and FeDyad 2) mainly differ in the covalent coupling of the two units, in
order to determine whether the nature of the different linker affects the photocatalytic
performance of the dyads. In FeDyad 1 the iron porphyrin (Cat) was covalently attached to
the RuII complex via an amide bond, while in FeDyad 2 through a triazole ring. Furthermore,
FeDyad 1 was tested as a photocatalyst in CO2 reduction systems. The results indicated that
in the case where only the dyad was used no CO2 reduction was detected. However, when
excess amount of unbound chromophore was added along with FeDyad 1 in the
photocatalytic systems, CO2 was reduced in CO with a satisfying turnover number (TON =310). The results of the ongoing photocatalytic experiments of FeDyad 2 as well as of some additional studies of FeDyad 1 are expected soon. Once all these studies are completed we will be able to draw safer conclusions regarding the mechanism of the catalytic process.
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Σύνθεση και μελέτη πορφυρινικών παραγώγων για φωτοκαταλυτική αναγωγή CO2
