Synthesis of highly pure poly(aryleneethnylene)s using palladium supported on calcium carbonate as an eco‐friendly heterogeneous catalyst

Metal catalyst contamination is a major concern in the preparation of polymeric materials. For conjugate polymers, trace amount of metal catalyst is detrimental to the optoelectronic properties. In this work, a method for synthesizing highly pure fluorescent polymers, poly(aryleneethynylene)s (PAEs), was developed using heterogeneous Pd/CaCO₃ catalytic system. Polymerization between a variety of aryl diethynes and aryl diiodides or dibromides were achieved using a catalytic amount of Pd/CaCO₃, CuI, and PPh₃ at 80 °C in good to excellent yields (79–100%). Resulting polymers possess degree of polymerization ranging from 8 to 50 with polydispersity index of 1.5–3.6. Importantly, PAEs from Pd/CaCO₃ catalytic system contain considerably lower level of Pd and Cu contamination (1.9 and 3.4 ppm, respectively) than those obtained from classical homogeneous catalyst, Pd(PPh₃)₄ and PdCl₂(PPh₃)₂ or heterogeneous catalyst Pd/C. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1556–1563     

Heat-Resistant Properties in the Phosphorescence of trans-Bis[β-(iminomethyl)aryloxy]platinum(II) Complexes: Effect of Aromaticity on d–π Conjugation Platforms

The heat-resistant properties towards thermal emission quenching of trans-bis[(β-iminomethyl)aryloxy]platinum(II) complexes bearing 3-iminomethyl-2-naphtholato- ( 1 ), 1-iminomethyl-2-naphtholato- ( 2 ), 2-iminomethyl-1-naphtholato- ( 3 ), and 2-iminomethyl-1-phenolato ( 4 ) moieties, and a mechanistic rationale of these properties, are described in this report. Complex 1 a , with N,N′-dipentyl groups, exhibits intense red emission in 2-methyl-2,3,4,5-tetrahydrofuran (2-MeTHF) at 298 K, whereas the analogues 2 a – 4 a are less or non-emissive under the same measurement conditions. All four complexes are highly emissive at 77 K. The heat-resistant properties toward thermal emission quenching (Φ_{298 K}/Φ_{77 K}) increase in the order 1 a (0.52)> 2 a (0.09)> 3 a (0.02)>> 4 a (0.00). We investigated the emission decay and thermal-deactivation processes using density functional theory (DFT), time-dependent (TD) DFT, and double-hybrid density functional theory (DHDF) calculations of N,N′-diethyl forms 1 b – 4 b , and discuss the results with a focus on the energy levels, molecular structures, and electronic configurations in the triplet excited states. The energy differences between the triplet metal–ligand charge transfer (³MLCT) state and minimum-energy crossing point between the lowest triplet state and singlet ground state (MECP) increase in the order 1 a > 2 a , 3 a > 4 a , consistent with the experimental results for the heat-resistant properties of these complexes. The origin of the present structure dependence of the ³MLCT–MECP energy gap is ascribed to the ease or difficulty of the high-lying d_σ* orbital participating in the MECP upon thermal structural distortion. The structure dependence in energy gaps between the π* and d_σ* orbitals, which is key for facilitating the thermal deactivation process, is rationally correlated with the extent of aromaticity on the coordination platforms ( 1 b >( 2 b , 3 b )> 4 b ).     

Water-Induced Breaking of the Coulombic Ordering in a Room-Temperature Ionic Liquid Metal Complex

Control of ion arrangements in ionic liquids represents a major challenge owing to the presence of the predominant coulombic interactions between cationic and anionic ion species that forms the coulombic ordering. Here, water-induced ion rearrangement in a room-temperature ionic liquid (RT-IL) metal complex, (1-ethyl-3-methylimidazolium)₂[MnN(CN)₄], is demonstrated through coordinative interactions between anions. Solidification occurred, which was associated with the formation of a “separated” structure consisting of cation columns and anionic cyanide-bridged one-dimensional coordination polymers. The energy diagram is in accord with the resultant RT-IL incorporating mononuclear [MnN(CN)₄]²⁻ molecules being a kinetic phase stabilized by inter-ion repulsions of the anionic divalent metal complex moieties. Water acts to decrease the coulombic interactions, including repulsion, giving rise to breaking of the coulombic ordering arising from coordination bond formation in the IL phase.     

Phosphorescence at Low Temperature by External Heavy-Atom Effect in Zinc(II) Clusters

Luminescent Zn^II clusters [Zn₄L₄(μ₃-OMe)₂X₂] (X=SCN ( 1 ), Cl ( 2 ), Br ( 3 )) and [Zn₇L₆(μ₃-OMe)₂(μ₃-OH)₄]Y₂ (Y=I⁻ ( 4 ), ClO₄⁻ ( 5 )), HL=methyl-3-methoxysalicylate, exhibiting blue fluorescence at room temperature (λ_max=416≈429 nm, Φ_em=0.09–0.36) have been synthesised and investigated in detail. In one case the external heavy-atom effect (EHE) arising the presence of iodide counter anions yielded phosphorescence with a long emission lifetime (λ_max=520 nm, τ=95.3 ms) at 77 K. Single-crystal X-ray structural analysis and time-dependent density-functional theory (TD-DFT) calculations revealed that their emission origin was attributed to the fluorescence from the singlet ligand-centred (¹LC) excited state, and the phosphorescence observed in 4 was caused by the EHE of counter anions having strong CH−I interactions.     

Solid-State Hydrogen-Bond Alterations in a [Co2Fe2] Complex with Bifunctional Hydrogen-Bonding Donors

A hydrogen-bonding donor–acceptor system, [Co₂Fe₂(bpy*)₄(CN)₆(tp*)₂](PF₆)₂⋅2ABA⋅4BN⋅2PE ( 1 s_olv ), was prepared by co-crystallization of an external stimuli-responsive cyanide-bridged tetranuclear [Co₂Fe₂] complex and bifunctional hydrogen-bonding donors, p-aminobenzoic acid. Compound 1 s_olv exhibited a gradual electron-transfer-coupled spin transition (ETCST), and the removal of solvent molecules led to an abrupt thermal ETCST behavior with increased transition temperature. X-ray structural analysis revealed that the modification of ETCST was caused by a significant alteration of a hydrogen-bonding mode between the tetranuclear [Co₂Fe₂]²⁺ cations and ABA molecules. Variable temperature IR measurements indicated that the desolvated form, 1 d_esolv , showed dynamic alteration of hydrogen-bonding interactions coupled with thermal ETCST behavior. These results suggested that the tetranuclear [Co₂Fe₂] complex shows solid-state modulations of hydrogen-bond strengths by external stimuli.     

Polymeric Design for Electron Transfer in Photoinduced Hydrogen Generation through a Coil–Globule Transition

To realize a renewable energy society, a polymeric system for photoinduced hydrogen generation utilizing a copolymer containing an electron acceptor was designed. In this system, the redox changes of viologen introduced into poly(N‐isopropylacrylamide) cause cyclic conformational changes owing to the shifting of the phase transition temperature (PTT). The polymeric coil–globule transitions with hydrophilic/hydrophobic changes accelerate the electron transfer for hydrogen generation. In particular, hydrogen generation using visible‐light energy with high efficiency is achieved around the PTT. In contrast to conventional solution systems, our polymeric system enables efficient hydrogen generation in a close molecular arrangement without the aggregation of catalytic nanoparticles. The utilization of conformational changes will provide a new strategy for synthesizing artificial photosynthetic hydrogels that split water to generate both hydrogen and oxygen.     

Flapping Peryleneimide as a Fluorogenic Dye with High Photostability and Strong Visible-Light Absorption

Flapping fluorophores (FLAP) with a flexible 8π ring are rapidly gaining attention as a versatile photofunctional system. Here we report a highly photostable “flapping peryleneimide” with an unprecedented fluorogenic mechanism based on a bent-to-planar conformational change in the S₁ excited state. The S₁ planarization induces an electronic configurational switch, almost quenching the inherent fluorescence (FL) of the peryleneimide moieties. However, the FL quantum yield is remarkably improved with a prolonged lifetime upon a slight environmental change. This fluorogenic function is realized by sensitive π-conjugation design, as a more π-expanded analogue does not show the planarization dynamics. With strong visible-light absorption, the FL lifetime response synchronized with the flexible flapping motion is useful for the latest optical techniques such as FL lifetime imaging microscopy (FLIM).     

A meta-Selective C−H Alumination of Mono-Substituted Benzene by Using An Alkyl-Substituted Al Anion through Hydride-Eliminating SNAr Reaction

Reaction of an Al-centered anion with toluene proceeded to form C−H cleaved product with a perfect meta-selectivity and a relatively small kinetic isotope effect (KIE, k_H/k_D=1.51). DFT calculations suggested a two-step reaction mechanism and electronically controlled meta-selectivity arising from the electron-donating methyl group. The reaction with other mono-substituted arenes was also investigated.     

Cycloaddition of Dialkylalumanyl Anion toward Unsaturated Hydrocarbons in (1+2) and (1+4) Modes

The reactivity of dialkylalumanyl anion ( 1 ) towards naphthalene, anthracene, diphenylacetylene, and (E)/(Z)-stilbenes was investigated. The compound 1 reacts with naphthalene and anthracene through (1+4) cyclization, giving Al-containing norbornadiene derivatives. In the reaction of 1 with diphenylacetylene and (E)/(Z)-stilbenes, (1+2) cyclization proceeded to form Al-C-C three-membered rings. Cyclization toward (E)- or (Z)-stilbenes solely gave a trans-cycloadduct. DFT calculations revealed that the cycloaddition of 1 with (Z)-stilbene proceeds via a single transition state with a carbanion character, which results in the selectivity towards the trans-cycloadduct.     

Algorithms for image recovery calculation in extended single-shot phase-shifting digital holography

Optical Review - The single-shot phase-shifting method of image recovery using an inclined reference wave has the advantages of reducing the effects of vibration, being capable of operating in real...