The principal theme evoked in this thesis is photo-induced electron transfer, as well as intramolecular and intraligand charge transfer. These processes are studied in different molecules and transition metal complexes. The motivation for studying the photophysical and photochemical properties of such complexes, in particular those containing bidentante ligands such as 2-2#-bipyridine (bpy) or 1,10-phenanthroline (phen) or their derivatives,[85-91] is their stability and their use for different applications, as for example in solar energy conversion [92-94] and molecular electronic devices.[95-97] It is also very interesting to study the effects of such systems combined with TTF as a subunit, the latter being involved in different processes, as exemplified above.
In Chapter 2 following the introduction, the main experimental methods used for the different processes and systems studied are described, such as absorption spectroscopy, techniques of oxidation and spectroelectrochemistry, luminescence spectroscopy as well as luminescence lifetime and transient absorption measurements.
This thesis being the result of a collaboration with Prof. Silvio Decurtins and Dr Shi-Xi Liu of the University of Bern, the synthesis and elementary characterisation of the compounds performed by them and their co-workers are not explicitly described in the general experimental section but are contained in the experimental parts of the individual manuscripts and chapters of the thesis.
Results on the series of ruthenium(II) compounds, [{Ru(bpy)2}n(TTF-ppb)](PF6)2n (n = 1, 2, ppb = dipyrido[2,3-a:3,,2,-c]phenazine), that were published in Inorganic Chemistry[98]
in 2008 are presented in Chapter 3. The intraligand charge transfer absorption band specific of TTF-ppb donor-acceptor molecule is discussed in conjunction with MLCT transitions and a variety of relaxation processes taking place in those complexes. In Chapter 4, the specific behaviour of these molecules is compared in an article published in Chimia[99] in 2007 with that of a similar but still different series of complexes:
[Ru(bpy)3-n(TTF-dppz)n]2+ (n = 1-3, dppz=dipyrido-[3,2-a:2#,3#-c]phenazine), which show a long-lived photo-induced charge separated state. In an attempt to better understand the long-lived charge transfer state and the mechanism by which it is created, another molecule in which a quinone unit was added as a ligand moiety:
[Ru(TTF-bridge). This work is described in chapter 5 in an article submitted to Inorganic Chemistry.[100] The work on donor-acceptor dyads containing TTF as electron donor and other organic moieties as acceptors but without metal coordination are presented in Chapters 6 and 7, in particular with regard to the specific absorption band of the intraligand charge transfer transition between TTF as electron donor and the other ligand moiety. In an article published in Chemistry – An Asian Journal [101] in 2009, the electronic interactions in the donor-acceptor assemblies with imidazole moieties were studied as a function of pH. The absorption spectra allowed the determination of the pKa for the different imidazole-annulated TTF systems in non-aqueous solvents. In the other article, published in Organic Letters [102] in 2009, the intraligand charge transfer in a TTF-perylenediimide (TTF-PDI) molecule was highlighted. In the last chapter, more recent studies on other transition metal ion complexes, namely of iron(II) and cobalt(II) complexed to TTF donor-acceptor ligands are presented, in order to study systems which combine photo-induced charge transfer and spin crossover phenomena. To finish, general conclusions summarize the work of this thesis. Some suggestions for further work will also be given.
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! 57 2. Experimental part
In this chapter the different spectroscopic techniques used for the determination of the photophysical and photochemical properties of the different molecules and complexes studied in this thesis are presented.