Published papers

Journal of the American Chemical Society 141(22), 8907 - 8913 (2019). doi:10.1021/jacs.9b02207

Molecular recognition of guest molecules within confined cavities enables effective modulation of their chemical and physical properties through noncovalent interactions. Because these modulated properties reflect the structural features of the host–guest assembly, the guest molecule can serve as a molecular probe to elucidate the origin of the host‐induced modulation. Herein, we report the formation of a host–guest complex composed of an emissive Ir(III) complex salt and a resorcin[4]arene host, along with the photophysical modulation of the guest via noncovalent interactions with the host. NMR spectroscopic analysis reveals a 1:1 binding stoichiometry, in contrast to the previously reported 6:1 stoichiometry, because the guest is larger than the cavity of the resorcin[4]arene hydrogen‐bonded hexameric capsule. This 1:1 binding mode is unambiguously confirmed by single‐crystal X‐ray diffraction analysis. The photoluminescent properties of the Ir(III) complex are enhanced in the presence of the host, indicating that electronic communication between the host and the guest plays a crucial role in modulating its photophysical behavior. These findings are further supported by density functional theory calculations. Overall, this article provides new insights into the photophysical dynamics of entrapped emitters and highlights the pivotal role of host–guest interactions in tuning emission properties.

A biscyclometalated Ir( iii ) complex bearing a triarylborane unit (IrDB) catalyzes the reduction of CO 2 to CO and HCOOH under visible light irradiation in the presence of 1,3-dimethyl-2-phenyl-2,3-dihydro-1 H -benzo[ d ]imidazole (BIH).

Encapsulation of coordination complexes within the confined spaces of self-assembled hosts is an effective method for creating supramolecular assemblies with distinct chemical and physical properties. Recent studies with calix-resorcin[4]arene hydrogen-bonded hexameric capsules revealed that encapsulated metal complexes exhibit enhanced and blue-shifted photoluminescence compared to their unencapsulated forms. The photophysical change has been hypothetically attributed to encapsulation-induced confinement, which isolates the metal complex from the solvent, suppressing stabilization of the excited state of the guest by solvent reorganization and structural relaxation, and altering the local environment, such as solvent polarity and viscosity, around the guest. In this study, density-functional theory calculations were conducted to explore how encapsulation affects the photophysical properties of a cationic iridium complex within a hydrogen-bonded hexameric capsule. The encapsulation-induced emission shift was analyzed by separating it into three factors: suppression of solvent reorganization, suppression of structural relaxation of the complex, and electronic interactions between the complex and the capsule. The findings indicate that the photoluminescence modulation is driven by the electronic interaction between the host and guest, which affects the energy levels of the molecular orbitals involved in the T1 excited state and the suppression of excited-state structural relaxation of the Ir complex due to the presence of the host. This study advances our understanding of the photophysical dynamics of coordination complexes within the confined spaces of hexameric capsules, providing a valuable approach for tuning the excited state properties of guest molecules.

Abstract A strategy to engineer the stacking of diketopyrrolopyrrole (DPP) dyes based on non‐statistical metallosupramolecular self‐assembly is introduced. For this, the DPP backbone is equipped with nitrogen‐based donors that allow for different discrete assemblies to be formed upon the addition of Pd(II), distinguished by the number of π‐stacked chromophores. A Pd3L6 three‐ring, a heteroleptic Pd2L2L′2 ravel composed of two crossing DPPs (flanked by two carbazoles), and two unprecedented self‐penetrated motifs (a Pd2L3 triple and a Pd2L4 quadruple stack), were obtained and systematically investigated. With increasing counts of stacked chromophores, UV/Vis absorptions red‐shift and emission intensities decrease, except for compound Pd2L2L′2, which stands out with an exceptional photoluminescence quantum yield of 51 %. This is extraordinary for open‐shell metal containing assemblies and explainable by an intra‐assembly FRET process. The modular design and synthesis of soluble multi‐chromophore building blocks offers the potential for the preparation of nanodevices and materials with applications in sensing, photo‐redox catalysis and optics.

Abstract A sterically controlled Z-shaped Pt2Ag2 complex showed a metalation reaction with a Ag ion via the formation of the thermodynamically unfavorable Pt2Ag2 complex with U-shaped configuration. Multiple dative bond formation between Pt and an additional Ag ion endowed enough thermodynamic stability on the Pt2Ag3 cluster to overcome the unfavorable steric effect from bulky substituents on the ligands in the U-shaped structure. A single crystal X-ray structural analysis revealed dimerized structure of the cationic Pt2Ag3 complex units bridged by [Ag2(OTf)4]2− (OTf− = triflate anion) via strong Ag–π coordination with pyrazole moiety in the solid state. The heteropolynuclear complexes showed photoluminescence properties depending on the structure of the Pt–Ag clusters.

Inspired by the efficiency displayed by enzymes, self-assembled cages with nanometer-sized cavities have been demonstrated as molecular flasks which can alter reaction pathways to show unusual activity and selectivity by the cavities. In contrast to numerous examples of organic reactions, organometallic catalysts within self-assembled cages are limited. Here, recent examples of gold(I)-catalyzed transformations within self-assembled cages are summarized. These results suggest that confined cavities that can encapsulate organometallic catalysts will provide and stabilize new active species for organometallic reactions which have previously been unobservable.

Herein, we report novel square-planar Pd(II) complexes bearing two Ag2(Ar2pz)3 units as self-assembled trans-chelating ligands. This structural motif is unique to Pd(II) ions and cannot be obtained from a Pt(II)...

Self‐assembly via noncovalent interactions can amplify small structural differences in small molecular units, producing large supramolecular architectures with structure‐dependent complexities and characteristics. In this paper, the unique self‐assembly behaviors of mononuclear Pt(II) complex units accommodating Ag(I) ions are reported. The Pt complex with the N^C chelating ligand and two different kinds of pyrazole ligands gave two regioisomers, whose structural difference was only the position of the N and C donor atoms in the N^C chelating ligands. This small structural difference influences the assembled structures with Ag ions, producing two different types of heteropolynuclear complexes with different clustering motifs. This was further amplified via a hierarchical assembly process incorporating additional Ag ions to afford two different types of Pt‐Ag cluster‐of‐cluster complexes. This study proves that the self‐assembly of unsymmetrical fragments can endow significant complexity and perturbation in the molecular system, enabling the observation of unique molecular behaviors.

Abstract A luminescent Ir(III) complex functionalized with a planar triarylborane moiety was prepared. This complex exhibits unique photophysical properties derived from the electron-withdrawing effect of the triarylborane moiety. A significant change in electron density occurs upon binding of F– to the electron-deficient boron center, resulting in decreased absorption and enhanced emission.