Abstract
Synthetic self‐assembly is a powerful technique for the bottom‐up construction of discrete and well‐defined polyhedral nanostructures resembling the spherical shape of large biological systems. In recent years, numerous Archimedean‐shaped coordination cages have been reported based on the assembly of bent monodentate organic ligands containing two or more distal pyridyl rings and square‐planar PdII ions. The formation of photoactive PdII metallamacrocycles and cages, however, remain rare. Here we report the first examples of emissive and homochiral supramolecular cages of the form [Ir8Pd4]16+. These cages provide a suitably sized cavity to host large guest molecules. Importantly, encapsulation and energy transfer have been observed between the blue‐emitting NBu4[Ir(dFppy)2(CN)2] guest and the red‐emitting Δ8‐[Ir8Pd4]16+ cage.
Highlights
Chemists have often found inspiration from the spontaneous and precise self-assembly exhibited by biological systems into giant, well-defined and functional superstructures.[1]
We report the first example of phosphorescent cages based on the self-assembly between two families of IrIII metalloligands of the form [Ir(C^N)2(qpy)]BF4 [where C^N is mesppy = 2-phenyl-4-mesitylpyridinato and dFmesppy = 2-(4,6difluorophenyl)-4-mesitylpyridinato, and qpy is 4,4’:2’,2’’:4’’,4’’’quaterpyridine] with Pd2+ ions through NpyÀPd coordination (Figure 1 a, b)
Each family of metalloligands is accessed in racemic form in a five step synthesis;[22] with the aim of assessing the impact of iridium-based chirality on the self-assembly, we prepared the enantiopure metalloligands L- and D-[Ir(mesppy)2(qpy)]BF4 (L-1 and D-1) and Land D-[Ir(dFmesppy)2(qpy)]BF4 (L-2 and D-2) by using l- and d-serine as chiral auxiliaries, following the protocol illustrated in Scheme S1 in the Supporting Information.[23]
Summary
To mediate biochemical transformations.[3] Much effort has been devoted to the preparation of large artificial nanostructures to mimic the precise assembly of multiple protein subunits into giant, polyhedral functional structures.[4] Nowadays, the self-assembly between square-planar palladium(II) or platinum(II) metal ions and complementary bent ligands containing positioned distal pyridine moieties, first demonstrated by Fujita et al.,[5] is one of the most popular and successful strategies to prepare molecular capsules or cages.[4b,6] These nanostructures generally possess well-defined internal cavities that promote the ingress of guest molecules and have been exploited in sensing,[7] gas storage and purification,[8] and catalysis.[9] Usually the metal ions play solely a structural role within these supramolecular architectures; more recently, there has been increasing interest in the investigation of photophysically active supramolecular architectures These have included systems that incorporate photophysically active metal ions as structural units within the architecture frameworks,[10] as well as those that employ ligand scaffolds decorated with photoactive units, including luminescent metal complexes.[11] Photoactive cages and metallamacrocycles provide restricted shape and size to govern host–guest interactions and, as a consequence of the optoelectronic communication between host and guest, distinct photophysical properties that are difficult to attain in conventional molecular materials can be achieved.[12]. Such photoactive homochiral assemblies have the potential to mediate enantioselective photocatalytic reactions and act as single white-light emissive materials
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