Encapsulation and Enhanced Luminescence Properties of IrIII Complexes within a Hexameric Self‐Assembled Capsule

Encapsulation and luminescence studies of [Ir(ppy)₂(bpy)]Cl (ppy=2‐phenylpyridinate, bpy=2,2′‐bipyridine) within a hexameric resorcinarene capsule are reported. One Ir^III complex cation was encapsulated within the capsule, as demonstrated by NMR and dynamic light scattering (DLS) studies. The emission color of the Ir^III complex was drastically changed from orange to yellow by encapsulation, in contrast with the lack of significant changes in the absorption spectrum. The hexameric capsule effectively hampers the non‐radiative pathway to increase both the luminescence quantum yield and the exited state lifetime. The luminescent properties of the encapsulated Ir^III complex depend on the ratio of Ir^III complex to the resorcinarene monomer as well as the concentration of resorcinarene monomer owing to the reversible process of self‐assembly of the hexameric capsule. Quenching experiments revealed that the Ir^III complex in the capsule was effectively separated from quenchers.     

Rational Design for Cooperative Recognition of Specific Nucleobases Using β‐Cyclodextrin‐Modified DNAs and Fluorescent Ligands on DNA and RNA Scaffolds

We propose a binary fluorimetric method for DNA and RNA analysis by the combined use of two probes rationally designed to work cooperatively. One probe is an oligonucleotide (ODN) conjugate bearing a β‐cyclodextrin (β‐CyD). The other probe is a small reporter ligand, which comprises linked molecules of a nucleobase‐specific heterocycle and an environment‐sensitive fluorophore. The heterocycle of the reporter ligand recognizes a single nucleobase displayed in a gap on the target labeled with the conjugate and, at the same time, the fluorophore moiety forms a luminous inclusion complex with nearby β‐CyD. Three reporter ligands, MNDS (naphthyridine–dansyl linked ligand), MNDB (naphthyridine–DBD), and DPDB (pyridine–DBD), were used for DNA and RNA probing with 3′‐end or 5′‐end modified β‐CyD – ODN conjugates. For the DNA target, the β‐CyD tethered to the 3′‐end of the ODN facing into the gap interacted with the fluorophore sticking out into the major groove of the gap site ( MNDS and DPDB ). Meanwhile the β‐CyD on the 5′‐end of the ODN interacted with the fluorophore in the minor groove ( MNDB and DPDB ). The results obtained by this study could be a guideline for the design of binary DNA/RNA probe systems based on controlling the proximity of functional molecules.     

Complete Photochromic Structural Changes in Ruthenium(II)?Diimine Complexes,Based on Control of the Excited States by Metalation

The thermal and photochemical reactions of a newly synthesized complex, [Ru^II(TPA)(tpphz)]²⁺ ( 1 ; TPA=tris(2‐pyridylmethyl)amine, tpphz=tetrapyrido[3,2‐a:2′,3′‐c:3′′,2′′‐h: 2′′′,3′′′‐j]phenazine), and its derivatives have been investigated. Heating a solution of complex 1 (closed form) and its derivatives in MeCN caused the partial dissociation of one pyridylmethyl moiety of the TPA ligand and the resulting vacant site on the Ru^II center was occupied by a molecule of MeCN from the solvent to give a dissociated complex, [Ru^II(η³‐TPA)(tpphz)(MeCN)]²⁺ ( 1′ , open form), and its derivatives, respectively, in quantitative yields. The thermal dissociation reactions were investigated on the basis of kinetics analysis, which indicated that the reactions proceeded through a seven‐coordinate transition state. Although the backwards reaction was induced by photoirradiation of the MLCT absorption bands, the photoreaction of complex 1′ reached a photostationary state between complexes 1 and 1′ and, hence, the recovery of complex 1 from complex 1′ was 67 %. Upon protonation of complex 1 at the vacant site of the tpphz ligand, the efficiency of the photoinduced recovery of complex 1 +H⁺ from complex 1′ +H⁺ improved to 83 %. In contrast, dinuclear μ‐tpphz complexes 2 and 3 , which contained the Ru^II(TPA)(tpphz) unit and either a Ru^II(bpy)₂ or Pd^IICl₂ moiety on the other coordination edge of the tpphz ligand, exhibited 100 % photoconversion from their open forms into their closed forms ( 2′ → 2 and 3′ → 3 ). These results are the first examples of the complete photochromic structural change of a transition‐metal complex, as represented by complete interconversion between its open and closed forms. Scrutinization by performing optical and electrochemical measurements allowed us to propose a rationale for how metal coordination at the vacant site of the tpphz ligand improves the efficiency of photoconversion from the open form into the closed form. It is essential to lower the energy level of the triplet metal‐to‐ligand charge‐transfer excited state (³MLCT*) of the closed form relative to that of the triplet metal‐centered excited state (³MC*) by metal coordination. This energy‐level manipulation hinders the transition from the ³MLCT* state into the ³MC* state in the closed form to block the partial photodissociation of the TPA ligand.     

Copolymer-grafted silica phase from a cation–anion monomer pair for enhanced separation in reversed-phase liquid chromatography

This work reports a new imidazolium and l-alanine derived copolymer-grafted silica stationary phase for ready separation of complex isomers using high-performance liquid chromatography (HPLC). For this purpose, 1-allyl-3-octadecylimidazolium bromide ([AyImC₁₈]Br) and N-acryloyl-l-alanine sodium salt ([AAL]Na) ionic liquids (IL) monomers were synthesized. Subsequently, the bromide counteranion was exchanged with the 2-(acrylamido)propanoate organic counteranion by reacting the [AyImC₁₈]Br with excess [AAL]Na in water. The obtained IL cation–anion monomer pair was then copolymerized on mercaptopropyl-modified silica (Sil-MPS) via a surface-initiated radical chain-transfer reaction. The selective retention behaviors of polycyclic aromatic hydrocarbons (PAHs), including some positional isomers, steroids, and nucleobases were investigated using the newly obtained Sil-poly(ImC₁₈-AAL), and octadecyl silylated silica (ODS) was used as the reference column. Interesting results were obtained for the separation of PAHs, steroids, and nucleobases with the new organic phase. The results showed that the Sil-poly(ImC₁₈-AAL) presented multiple noncovalent interactions, including hydrophobic, π–π, carbonyl–π, and ion–dipole interactions for the separation of PAHs and dipolar compounds. Only pure water was sufficient as the mobile phase for the separation of the nucleobases. Ten nucleosides and bases were separated, using only water as the mobile phase, within a very short time using the Sil-poly(ImC₁₈-AAL), which is otherwise difficult to achieve using conventional hydrophobic columns such as ODS. The combination of electrostatic and hydrophobic interactions are important for the effective separation of such basic compounds without the use of any organic additive as the eluent on the Sil-poly(ImC₁₈-AAL) column.

Formation of Hierarchical Lamellae‐in‐Lamella Nanostructures from Polymer Blends Via Controlled Nonequilibrium Freezing

The creation of hierarchical nanostructures in polymeric materials has been intensively studied due to the great potential to tailor their physicochemical properties. Although much success has been achieved over the past decades in block copolymers, hierarchical structure engineering in polymer blends remains a great challenge. Here, the formation of hierarchical lamellae‐in‐lamella nanostructures from polymer blends via controlled nonequilibrium freezing is reported. Polymer blends are first dissolved in molten hexamethylbenzene (HMB) to form a homogeneous melt. When cooled to below its melting temperature, the HMB is crystallized and depleted, and the polymers are directionally solidified. This process is rapid enough that phase separation of the polymer blends is kinetically trapped at the nanoscale level. Then, the polymer blend epitaxially crystallizes onto the HMB inside the nanophase, resulting in the hierarchical lamellae‐in‐lamella structure. This structure is stable under ambient conditions and tunable depending on the annealing temperature and blending ratio.

     

Humidity-responsive thermal conduction properties of bacterial cellulose films

Cellulose - High hygroscopicity is an unavoidable feature of cellulose materials, and it is important for clarifying the humidity dependence of the target function toward precise utilization....     

Probing the Rotational Dynamics of meso‐(2‐Substituted)aryl Substituents in A2B‐Type Subporphyrins

A₂B‐type B‐methoxy subporphyrins 3 a – g and B‐phenyl subporphyrins 7 a – c , e , g bearing meso‐(2‐substituted)aryl substituents are synthesized, and their rotational dynamics are examined through variable‐temperature (VT) ¹H NMR spectroscopy. In these subporphyrins, the rotation of meso‐aryl substituents is hindered by a rationally installed 2‐substituent. The rotational barriers determined are considerably smaller than those reported previously for porphyrins. Comparison of the rotation activation parameters reveals a variable contribution of ΔH^≠ and ΔS^≠ in ΔG^≠. 2‐Methyl and 2‐ethyl groups of the meso‐aryl substituents in subporphyrins 3 e , 3 f , and 7 e induce larger rotational barriers than 2‐alkoxyl substituents. The rotational barriers of 3 g and 7 g are reduced by the presence of the 4‐dibenzylamino group owing to its ability to stabilize the coplanar rotation transition state electronically. The smaller rotational barriers found for B‐phenyl subporphyrins than for B‐methoxy subporphyrins indicate a negligible contribution of S_N1‐type heterolysis in the rotation of meso‐aryl substituents.     

Novel thermal reaction of Fischer carbene complexes with imines: synthesis of beta-methoxy allylic amine derivatives

[formula: see text] Alkyl-substituted chromium Fischer carbene complexes were found to react with various N-tosylimines to give beta-methoxy allylic amine derivatives under thermal conditions. This result is essentially distinct from the photochemical outcome in which beta-lactam derivatives are obtained.