Synthesis of Chromophore Decorated Ligands and their Self-Assembly into Supramolecular Coordination Complexes

Abstract

This thesis is concerned with the synthesis and characterization of chromophore decorated self-assembled coordination complexes (SCC’s). The SCC’s were constructed from ditopic bispyridine ligands as organic donor building blocks and tetravalent Pd(II) ions as an inorganic acceptor building block, following the molecular library approach. <br /> To access ligands featuring a chromophoric BODIPY moiety in the <em>exo</em>-position, as well as linear alkoxy chains of various lengths in the <em>endo</em>-position, an efficient diversity oriented synthetic strategy was developed. The yield of the BODIPY synthesis in an early synthetic step could be drastically improved from ca. 10 to 20 %, in earlier works, to a typical yield of 50 to 60 % in this work. This enabled the convenient gram scale preparation of an <em>exo</em>-BODIPY decorated protoligand, which could be diversified into the target ligands <em>via Williamson</em> ether synthesis in the final synthetic step. In a similar fashion, a final stage <em>endo</em>-diversification of analogous <em>exo</em>-anthracene decorated ligands could be realized. <br /> Ligands with parallel coordination vectors were found to assemble into dinuclear [Pd₂L₄] complexes, independent of the nature of the surveyed <em>endo</em>-substituents, as indicated by ¹H-NMR, ¹H-DOSY-NMR and ESI-MS. Interestingly, the <em>endo</em>-functions fold into the pockets between neighboring ligands, as revealed by the crystal structure of the <em>exo</em>-BODIPY, <em>endo</em>-hexyloxy substituted derivative. With increasing <em>endo</em>-alkoxy chain lengths, a 1:1 ¹H-NMR-signal splitting for protons on the <em>exo</em>-BODIPY unit is noted, which was investigated via variable temperature 1H-NMR, revealing a temperature dependency of the observed splitting. To rationalize this effect, four isomeric, inter-converting [Pd₂L₄] structures differing in the relative orientation of the alkoxy chains within the pockets is proposed. Furthermore, bulky acetyl and para-methoxybenzyl groups in the <em>endo</em>-position were probed for their ability to induce 1:3 self-sorting via cavity occupation. <br /> Ligands with 120° coordination vectors were employed to assemble [Pd₁₂L₂₄] molecular spheres, decorated with BODIPY and anthracene moieties in the <em>exo</em>-positions. By mixing ligands differing in the distance between coordination sites, a size complimentary approach for the self-sorting into a [Pd₁₂L₁₂L’₁₂] complex was followed. The circular arrangement of the chromophores in this complex is reminiscent of the organization of pigments in the light harvesting antenna systems of photosynthetic organisms and represents a first step in the construction of a synthetic analogue, potentially featuring a multi step energy transfer cascade.