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Photoinduced electron transfer across ortho-oligo-phenylenes and novel luminophores based on earth-abundant metals

Malzkuhn, Sabine Marie. Photoinduced electron transfer across ortho-oligo-phenylenes and novel luminophores based on earth-abundant metals. 2018, Doctoral Thesis, University of Basel, Faculty of Science.

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Official URL: http://edoc.unibas.ch/diss/DissB_12922

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Abstract

Long-range electron-transfer is of high interest for many fields, such as artificial photosynthesis and molecular electronics. Donor – bridge – Acceptor compounds, wherein photoinduced electron transfer takes place were thoroughly investigated in this regard. Especially para-phenylene systems were chosen due to their rigid, rod-like wire behaviour. Depending on the electronic coupling of the bridge, para-phenylenes reveal �-values ranging from 0.2 to 0.8 °A−1. Their ortho-connected relatives are completely unexplored until now. In chapter I of this thesis the motivation for this work and the theoretical background for electron transfer will be given. This will be followed by a few examples of electron transfers across para-phenylenes, to put the herein presented work into perspective. In chapter II photoinduced
electron-transfer across an ortho-phenylene wire consisting of 2 to 6 phenyl units will be presented. A Ru(II)-photosensitiser and a triarylamine electron donor were chosen to investigate the kinetics of the charge-shift reaction. The photoinduced forward, as well as the
thermal back-reaction, were explored with time resolved measurements. Due to the flexibility of the bridge and slowly interconverting conformers in solution, analysis of charge-separation
remains turbid, but a coherent analysis can be made for charge-recombination. The main discovery is that ortho-phenylenes possess very low �-values for charge-transfer, with a �-value in acetonitrile of 0.04 °A−1. The mechanism for the hole transfer is coherent tunnelling and a relevant aspect seems to be the �-pathway, which is shorter for ortho-phenylenes than for para-phenylenes. Ortho-phenylenes can therefore be considered as a new class of molecular wires. Chapter III will then present the results of photoinduced long-range electron transfer through ortho-naphthalenes, which can form different atropisomers and electron transfer is studied in these systems for the first time.
Photoinduced electron transfer would not be possible without photosensitisers, which allow for an enough long living excited state with enough reducing or oxidising power, that electron transfer reactions can take place. Most photosensitisers today which reach the photophysical goals for being applied, for example in photoredox catalysis or in long-range electron transfer, rely on noble metals, such as Ru(II) or Ir(III). Therefore it would be desirable, to shift from noble metals as centres to more earth abundant metals. Nickel(0) allows for an MLCT transition when the ligand orbitals are of the right energy. In chapter IV first preliminary results of a nickel(0) bis(diphenylphosphino)naphthalene complex will be presented, which
were accompanied by DFT calculations.
Following this approach of using more earth-abundant metals, in chapter V the possibility of titanium(IV) complexes is considered, which could possibly undergo LMCT emission transitions. Different possible approaches towards a titanium-based luminophore will be given.
Advisors:Wenger, Oliver S. and Decurtins, Silvio
Faculties and Departments:05 Faculty of Science > Departement Chemie > Chemie > Anorganische Chemie (Wenger)
Item Type:Thesis
Thesis Subtype:Doctoral Thesis
Thesis no:12922
Thesis status:Complete
Bibsysno:Link to catalogue
Number of Pages:1 Online-Ressource (xi, 127 Seiten)
Language:English
Identification Number:
Last Modified:25 Jan 2019 05:30
Deposited On:24 Jan 2019 10:23

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