A variety of π‐electronic ion‐pairing assemblies can be constructed by combining anion complexes of π‐electronic systems and countercations. In this study, a series of anion‐responsive π‐electronic molecules, dipyrrolyldiketone PtII complexes containing a phenylpyridine ligand, were synthesized. The resulting PtII complexes exhibited phosphorescence emission, with higher emission quantum yields (0.30–0.42) and microsecond‐order lifetimes, and solution‐state anion binding, as revealed by our spectroscopic analyses. These PtII complexes displayed solid‐state ion‐pairing assemblies, exhibiting various anion‐binding modes, which derived from pyrrole‐inverted and pyrrole‐non‐inverted conformations, and packing structures, with the contribution of charge‐by‐charge assemblies, which were dependent on the substituents in the PtII complexes and the geometries and electronic states of their countercations.
Dipyrrolyldiketone BF complexes with amide units at pyrrole α-positions were synthesized in modest yields and showed extremely high anion-binding affinities because of multiple hydrogen-bonding interactions. The phenyl-amide-substituted derivative formed solid-state chiral helical structures, wherein π planes were oriented parallel to the helical directions. Examination of anion-binding behavior using H NMR spectroscopy combined with theoretical studies suggested fast pyrrole inversions, particularly for the phenyl-amide-substituted derivative. The anion complexes behaved as building units of ion-pairing assemblies in combination with planar and bulky cations.
Arylpyrrolyldiketone boron complexes as anion-responsive π-electronic molecules were synthesized by Claisen condensations of acetylpyrrole and corresponding aryl esters. The synthesized π-electronic molecules exhibited anion-binding behavior with various binding modes including pyrrole-inverted and non-inverted [1+1]-type anion complexes as well as [2+1]-type complexes owing to the presence of only a single pyrrole ring. Furthermore, solid-state ion-pairing assemblies, comprising receptor-anion complexes and countercations, were constructed based on fairly planar [2+1]-type complexes.
Nitro-substituted π-electronic molecules are fascinating because of their unique electronic and optical properties and the ease of their transformation into various functional derivatives. Herein, nitro-introduced dipyrrolyldiketone BF2 complexes as anion-responsive π-electronic molecules were synthesized, and their electronic properties and anion-binding abilities were investigated by spectroscopic analyses and theoretical studies. The obtained nitro-substituted derivatives showed solvent-dependent UV/vis spectral changes and high anion-binding affinities due to the easily pyrrole-inverted conformations and polarized pyrrole NH sites upon the introduction of electron-withdrawing moieties.
Synthesis of dipyrrolyldiketone PtII complexes, as phosphorescence anion‐responsive π‐electronic molecules, was motivated by the chemistry of previously investigated boron complexes. The PtII complexes displayed solid‐state ion‐pairing assemblies, exhibiting various anion‐binding modes, derived from pyrrole‐inverted and pyrrole‐non‐inverted conformations, and packing structures, with the contribution of charge‐by‐charge assemblies. More information can be found in the Full Paper by H. Maeda et al. (DOI: 10.1002/chem.202100855).
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