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Identifier

000403926

Title

Hybrid porphyrin complexes with ruthenium for catalytic oxidations

Alternative Title

Υβριδικά πορφυρινικά σύμπλοκα με ρουθήνιο για καταλυτικές οξειδώσεις

Author

Μαργιώλα, Σοφία Π.

Thesis advisor

Κουτσολέλος, Αθανάσιος

Reviewer

Μήλιος, Κωνσταντίνος
Tron, Thierry

Abstract

The sustainable production of clean energy constitutes one of the most important scientific challenges of the 21st century. Currently, the major part of the global energy supply is provided by carbon-based energy sources, which are connected to severe environmental issues, such as air pollution and the greenhouse effect. Consequently, it is crucial to turn to clean and environmentally friendly carbon-neutral alternatives that have the potential to meet the needs of present and future generations. In fact, every hour the sun provides our planet with more energy than what is consumed during a whole year. This fact has mesmerized researchers and makes the conversion of solar energy into fuel and electricity one of the most promising solutions to this problem. Photosynthetic organisms are ubiquitous in nature; they are responsible for the development and sustenance of all life on Earth. They may be quite different, but all of them use the same basic strategy, in which light is initially absorbed by antenna proteins containing many chromophores, followed by energy transfer to a specialized reaction center protein, in which the captured energy is converted into chemical energy by means of electron-transfer reactions. However, for an artificial system, a more practical approach would be to use solar energy to split H2O into molecular oxygen and hydrogen. This process requires the coupling of the two half-reactions: (i) oxidation of H₂O to generate the reducing equivalents (electrons) and (ii) reduction of protons to molecular hydrogen. Harnessing solar energy for the photoproduction of renewable fuels therefore requires interfacing several fundamental but challenging photophysical steps with complicated catalytic transformations. In this thesis, the synthesis of a porphyrin–RuII polypyridine complexes where the porphyrin acts as a photoactive unit and the RuII polypyridine as a catalytic precursor is described. Comparatively, the free base porphyrin was found to outperform the ruthenium based chromophore in the yield of light induced electron transfer. Mechanistic insights indicate the occurrence of a pingpong energy transfer from the ¹LC excited state of the porphyrin chromophore to the ³MCLT state of the catalyst and back to the ³LC excited state of the porphyrin unit. The latter, triplet–triplet energy transfer back to the chromophore, efficiently competes with fast radiationless deactivation of the excited state at the catalyst site. The energy thus recovered by the chromophore allows improved yield of formation of the oxidized form of the chromophore and concomitantly of the oxidation of the catalytic unit by intramolecular charge transfer. Also the catalytic properties of the dyads were investigated through photocatalytic reactions, using organic compounds as substrates for oxidative reactions.

Language

English

Subject

Organic substrates

Photocatalysis

Οργανικά υποστρώματα

Φωτοκατάλυση

Issue date

2016-11-18

Collection

School/Department--School of Sciences and Engineering--Department of Chemistry--Post-graduate theses

Type of Work--Post-graduate theses