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π-π Interactions are established as a powerful supramolecular tool, whereas the usability of CH-π interactions has been rather limited so far. Here we present (i) selective binding of planar polyaromatics and (ii) effective isolation of planar metal complexes by a polyaromatic capsule, utilizing multiple CH-π interactions. In the spheroidal cavity, one molecule of large and medium-sized polyaromatic molecules (i. e., coronene and pyrene) is exclusively bound from mixtures bearing the same number of aromatic CH groups. Theoretical studies reveal that multiple host-guest CH-π interactions (up to 32 interactions) are the predominant driving force for the observed selectivity. In addition, one molecule of planar metal complexes (i. e., porphine and bis(acetylacetonato) Cu(II) complexes) is quantitatively bound by the capsule through aromatic and aliphatic CH-π multi-interactions, respectively. The ESR and theoretical studies demonstrate the isolation capability of the capsular framework and an unusual polar environment in the polyaromatic cavity.

In this work, the design, synthesis, and single-molecule conductance of ethynyl- and butadiynyl-ruthenium molecular wires with thioether anchor groups [RS=n-C6 H13 S, p-tert-Bu-C6 H4 S), trans-{RS-(C≡C)n }2 Ru(dppe)2 (n=1 (1R ), 2 (2R ); dppe: 1,2-bis(diphenylphosphino)ethane) and trans-(n-C6 H13 S-C≡C)2 Ru{P(OMe)3 }4 3hex ] are reported. Scanning tunneling microscope break-junction study has revealed conductance of the organometallic molecular wires with the thioacetylene backbones higher than that of the related organometallic wires having arylethynylruthenium linkages with the sulfur anchor groups, trans-{p-MeS-C6 H4 -(C≡C)n }2 Ru(phosphine)4 4n (n=1, 2) and trans-(Th-C≡C)2 Ru(phosphine)4 5 (Th=3-thienyl). It should be noted that the molecular junctions constructed from the butadiynyl wire 2R , trans-{Au-RS-(C≡C)2 }2 Ru(dppe)2 (Au: gold metal electrode), show conductance comparable to that of the covalently linked polyynyl wire with the similar molecular length, trans-{Au-(C≡C)3 }2 Ru(dppe)2 63 . The DFT non-equilibrium Green's function (NEGF) study supports the highly conducting nature of the thioacetylene molecular wires through HOMO orbitals.

Herein, we report synthesis, electrochemical and photophysical properties of aromatic hydrocarbons having one and two dimesitylborylethynyl peripherals 1 and 2 . The mono- ( 1 ) and di-boryl compounds ( 2 ) readily prepared by nucleophilic substitution reaction are fairly stable to air and moisture in the solid-state. The inserted ethynediyl (C ≡C) spacer cancels steric hindrance between the bulky dimesitylboryl groups and the aromatic rings, leading to effective π -conjugation over the B - C ≡ C -Ar linkages as revealed by cyclic voltammetry. Despite the small structural differences, photophysical properties of the benzene, naphthalene, and anthracene derivatives were different. Virtually no emission was observed for the benzene derivatives, whereas the anthracene derivatives emitted with high quantum yields both in solution and solid states. Notably, the naphthalene derivatives showed aggregation-induced emission behavior. Unlike common sterically congested triarylborane derivatives reported so far, the anthracene derivatives showed π - π * type absorption and emission bands, which derived from the efficient intramolecular orbital interactions between the boron centers and the anthracene moieties as supported by the density functional calculations. As a result, the dimesitylborylethynyl substituents effectively lowers the LUMO levels of the aromatic hydrocarbon parts while the HOMO levels are almost unaffected, leading to materials with controllable HOMO-LUMO gaps.

To explore new cavity functions, we herein employed cis-trans stereoisomers with a N=N, C=C, or C=N unit as guest indicators for a polyaromatic capsule. Thanks to the rigid, spherical cavity with a diameter of ∼1 nm, azobenzene and stilbene derivatives are quantitatively encapsulated by the capsule with 100 % cis-selectivity in water. The isomerization of the cis-azo compound is suppressed against heat and light in the cavity, due to the confinement effect. Furthermore, C,N-diphenyl imine derivatives are quantitatively encapsulated by the capsule in water and adopt an otherwise unstable cis-form. The polyaromatic cavity suppresses the hydrolysis of the imines in water, even at elevated temperature, due to the shielding effect. Accordingly, the properties of the cis-trans isomers could be largely altered through supramolecular manipulation.

Host-guest interactions of a molecular tweezer complex 1 with various planar organic molecules including polyaromatic hydrocarbons (PAHs) were investigated by 1D and 2D (1)H NMR spectroscopy, UV/Vis absorption and emission titration studies. 2D and DOSY NMR spectroscopies support the sandwiched binding mode based on 1:1 host-guest interactions. The binding constants (K(S)) of complex 1 for various PAHs were determined by NMR titration studies and the values were found to span up to an order of 10(4) M(-1) for coronene to no observable interaction for benzene, indicating that the π-surface area is important for such host-guest interactions. The substituent effect on the host-guest interaction based on the guest series of 9-substituted anthracenes was also studied. In general, a stronger interaction was observed for the anthracene guest with electron-donating groups, although steric and π-conjugation factors cannot be completely excluded. The photophysical responses of complex 1 upon addition of various PAHs were measured by UV/Vis and emission titration studies. The UV/Vis absorption spectra were found to show a drop in absorbance of the metal-to-ligand charge-transfer (MLCT) and ligand-to-ligand charge-transfer (LLCT) admixture band upon addition of various guest molecules to 1, whereas the emission behavior was found to change differently depending on the guest molecules, showing emission enhancement and/or quenching. It was found that emission quenching occurred either via energy transfer or electron transfer pathway or both, while emission enhancement was caused by the increase in rigidity of complex 1 as a result of host-guest interaction.