Authors: Regeni, Irene
Title: Dye-based coordination cages
Language (ISO): en
Abstract: Synthetic organic dyes find broad use in industry (e.g. as colorizing agents and laser materials), medicine (e.g. as diagnostic tools and drugs) and research (e.g. in fluorescence microscopy, FRET setups and as photosensitizers). All the applications originate from the typical interaction that these chromophores have with visible light. However, while a number of these dyes is produced on a multi ton scale since decades, their implementation into complex chemical systems and nano structures still offers unexploited potential for the development of novel functional devices and materials. In particular, their synthetic incorporation into self-assembled supramolecular systems is rather rarely found. The combination of the two concepts would lead to functional architectures with interesting photophysical and redoxchemical properties that could be utilized for diagnostic and catalytic applications. Hence, this thesis aims at delivering an unprecedented design and implementation of organic dyes into nano-sized coordination cages to enrich them with the feature to strongly interact with visible light. New bis-monodentate ligands were designed based on a selection of dyes, namely diketopyrrolopyrroles (DPP) and members of the coal-tar dye family: Michler’s ketone, rhodamine B, methylene blue and crystal violet. The incorporation of these dye functionalities into metallo-supramolecular architectures was achieved through coordination of the newly developed ligands to Pd(II) cations. Structural and optical properties of the assemblies were evaluated and fully characterized with a wide range of spectroscopic, spectrometric and diffraction techniques. Interesting optical features were found for DPP-based homoleptic and heteroleptic assemblies. From the structural point of view, a new topology of a homoleptic [Pd2L4] cage was revealed and characterized by an atypical arrangement of the four ligands around the Pd-axis in order to promote π-stacking of the four chromophores. Furthermore, cage-to-cage transformations were observed for a combination of three different ligands (DPP-based, carbazole-based and dimethylfluorene-based as optically relevant moieties). The introduction of the coal-tar dyes moieties into bis-pyridine or bis-isoquinoline ligands required a careful design to allow retainment of their specific absorption properties. Typical alkyne bridges between donor groups and backbones would have hampered the electronic structure of the parental dyes. Therefore, the new ligand design used in this thesis exploited piperazine linkers. By coordination to the square planar metal cations, lantern-shaped and helically twisted, visible light-absorbing [Pd2L4] cages were obtained. Their remarkable absorption properties were exploited for the recognition of small chiral molecules. Encapsulation or even only external association caused the chromophore-based cages to populate a chiral conformation and the effect was measured with CD spectroscopy. Moreover, some promising results were obtained in the recognition of bio-relevant anionic molecules where one specific lantern-shaped cage, based on the rhodamine B dye, exhibited impressive ellipticities. Important results were obtained in the field of supramolecular DNA recognition by employing the newly synthesized methylene blue-based Pd-helicate. Besides the preferential interaction of double-stranded DNA for one helical handedness of the artificial binding agent, focus was set on the class of G quadruplexes. Several different topologies were analysed in combination with the helicate to understand the origin of selective structural recognition. A notable selectivity was found for the sequence c-Myc27, part of the promoter region of oncogene c-MYC, and its derivatives. Even if the recognition process was not yet elucidated in atomistic detail, the new findings spur its application potential. The implementation of organic dye functionalities was proven to be a successful strategy to expand cage properties that arise from the interaction with visible light. New structural motifs, with interesting optical properties and applicability in chiral recognition of both small molecules and DNA have been developed. This work opens new possibilities of exploring light-driven processes such as photoinduced energy or electron transfer and their application in the field of photo-redox supramolecular catalysis.
Subject Headings: Coordination cages
DNA supramolecular recognition
Chirality transfer
Subject Headings (RSWK): DNA
Issue Date: 2020
Appears in Collections:Lehrstühle für Anorganische Chemie

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