Strong Solid‐state Luminescence Enhancement in Supramolecular Assemblies of Polyoxometalate and “Aggregation‐Induced Emission”‐active Phospholium

Two new supramolecular fluorescent hybrid materials, combining for the first time [M₆O₁₉]^2? (M=Mo, W) polyoxometalates (POMs) and aggregation‐induced emission (AIE)‐active 1‐methyl‐1,2,3,4,5‐pentaphenyl‐phospholium ( 1⁺ ), were successfully synthesized. This novel molecular self‐assembling strategy allows designing efficient solid‐state emitters, such as (1)₂[W₆O₁₉] , by directing favorably the balance between the AIE and aggregation‐caused quenching (ACQ) effects using both anion‐π⁺ and H‐bonding interactions in the solid state. Combined single‐crystal X‐ray diffraction, Raman, UV‐vis and photoluminescence analyses highlighted that the nucleophilic oxygen‐enriched POM surfaces strengthened the rigidity of the phospholium via strong C?H???O contacts, thereby exalting its solid‐state luminescence. Besides, the bulky POM anions prevented π–π stacking interactions between the luminophores, blocking detrimental self‐quenching effects.     

Effects of Intermolecular Interactions on Luminescence Property in Organic Molecules

The organic solid-state lightemitting materials have attracted more and more attention owing to their promising applications in displays, lasers and optical communications. In contrast to isolated molecule, there are various weak intermolecular interactions in organic solids that sometimes have a large impact on the excited-state properties and energy dissipation pathways, resulting in strong fluorescence/phosphorescence. It is increasingly necessary to reveal the luminescence mechanism of organic solids. Here, we briefly review how intermolecular interactions induce strong normal fluorescence, thermally activate delayed fluorescence and room-temperature phosphorescence in organic solids by examining changes in geometry, electronic structures, electron-vibration coupling and energy dissipation dynamics of the excited states from isolated to aggregated molecules. We hope that the review will contribute to an in-depth understanding of the excited state properties of organic solids and to the design of excellent solid-state light-emitting materials.     

B(C6F5)3: A Lewis Acid that Brings the Light to the Solid State

The straightforward coordination of the Lewis acid B(C₆F₅)₃ to classical, non‐emitting aldehydes results in solid‐state photoluminescence. Variation of the electronic properties of the carbonyl moieties lead to the modulation of the solid‐state emission colors, covering the entire visible spectrum with quantum yields up to 0.64. Steady‐state spectroscopy in combination with X‐ray diffraction analysis and DFT calculations confirm that intermolecular interactions between the Lewis adducts are responsible for the observed luminescence. Alteration of the latter interactions induces, moreover, remarkable solid‐state phenomena such as piezochromism. The versatility and simplicity of our approach facilitate the future development of solid‐state emitting materials.     

Electronic Circular Dichroism Imaging (ECDi) Casts a New Light on the Origin of Solid-State Chiroptical Properties

Solid-state ECD (ss-ECD) spectra of a model microcrystalline solid, finasteride, dispersed into a KCl pellet were recorded by using the synchrotron radiation source at the Diamond B23 beamline. Scanning a surface of 36 mm² with a step of 0.5 mm, we measured a set of ECD imaging (ECDi) spectra very different from each other and from the ss-ECD recorded with a bench-top instrument (1 cm² area). This is due to the anisotropic part of the ECD (ACD), which averages to zero in solution or on a large number of randomly oriented crystallites, but can otherwise be extremely large. Two-way singular value decomposition (SVD) analysis, through experimental and simulated TDDFT spectra, disclosed that the measured and theoretical principal components are in line with each other. This finding demonstrates that the observed isotropic ss-ECD spectrum is governed by the anisotropy of locally oriented crystals. It also introduces a new quality for ss-ECD measurements and opens a new future for probing and mapping chiral materials in the solid state such as active pharmaceutical ingredients (APIs).     

Shedding Light on the Diverse Reactivity of NacNacAl with N-Heterocycles

The aluminum(I) compound NacNacAl (NacNac=[ArNC(Me)CHC(Me)NAr]⁻, Ar=2,6-iPr₂C₆H₃, 1 ) shows diverse and substrate-controlled reactivity in reactions with N-heterocycles. 4-Dimethylaminopyridine (DMAP), a basic substrate in which the 4-position is blocked, induces rearrangement of NacNacAl by shifting a hydrogen atom from the methyl group of the NacNac backbone to the aluminum center. In contrast, C−H activation of the methyl group of 4-picoline takes place to produce a species with a reactive terminal methylene. Reaction of 1 with 3,5-lutidine results in the first example of an uncatalyzed, room-temperature cleavage of an sp² C−H bond (in the 4-position) by an Al^I species. Another reactivity mode was observed for quinoline, which undergoes 2,2′-coupling. Finally, the reaction of 1 with phthalazine produces the product of N−N bond cleavage.     

手性有机小分子圆偏振发光的研究进展

圆偏振发光不仅能直观地反映手性发光体系的激发态结构信息,而且在3D显示、自旋信息通讯、信息存储与处理、CPL激光、生物探针等领域具有广泛的应用前景.因此,近年来圆偏振发光材料引起了人们越来越多的兴趣与关注,成为有机发光功能材料领域一个新的研究热点.本综述总结近年来关于手性有机小分子圆偏振发光的研究进展,主要围绕具有中心手性、轴手性、面手性和螺旋手性的圆偏振发光有机小分子展开介绍.     

Templated growth of hybrid structures at the peptide-peptide interface

This study describes the use of peptide vesicular platforms for the templated growth of fibrillar structures to craft hybrids that retain the gross morphological features of two discreet self-assembled peptides. A synthetic triskelion peptide, which results in the rapid emergence of self-assembled spherical structures, was employed as a template. Addition of either one of two different peptides, both of which form long filamentous structures when co-incubated with the triskelion solution, affords hybrids that retain the gross morphology of both the spherical and filamentous structures. It is surmised that this process is aided by hydrogen bonding and the interdigitation of aromatic residues, which leads to the growth of hybrid structures. We believe that observations concerning the surface-assisted growth of peptide fibrils and tubular structures from vesicular platforms may have ramifications for the design and development of peptide-based hybrid materials with controlled hierarchical structures.     

A Theoretical Analysis of the Potential Role of π–π Stacking Interactions in the Photoprotolytic Cycle of Firefly Luciferin

Firefly oxyluciferin is a photoacid that presents a pH‐sensitive fluorescence, which results from pH‐dependent changes on the conformation of self‐aggregated π–π stacking complexes. Luciferin is a derivative of oxyluciferin with very similar fluorescence and photoacidic properties. This similarity indicates that luciferin is also expected to be able to form π–π stacking complexes, but no pH‐sensitive fluorescence is found for this compound. Here, a theoretical approach is used to rationalize this finding. We have found that luciferin only forms π–π stacking complexes in the ground state at acidic pH. At basic pH and in the excited state, luciferin is present as a dianion. This species is not able to self‐aggregate, owing to repulsive electrostatic interactions. Thus, this emissive species is not subject to π–π stacking interactions; this explains its pH‐insensitive fluorescence.     

Solubilization of single-walled carbon nanotubes by using polycyclic aromatic ammonium amphiphiles in water--strategy for the design of high-performance solubilizers

We describe the design of polycyclic aromatic compounds with high performance that dissolve single-walled carbon nanotubes (SWNTs). Synthetic amphiphiles trimethyl-(2-oxo-2-phenylethyl)-ammonium bromide (1) and trimethyl-(2-naphthalen-2-yl-2-oxo-ethyl)-ammonium bromide (2) carrying a phenyl or a naphtyl moiety were not able to dissolve/disperse SWNTs in water. By contrast, trimethyl-(2-oxo-2-phenanthren-9-yl-ethyl)-ammonium bromide (3) solubilized SWNTs, although the solubilization ability was lower than that of trimethyl-(2-oxo-2-pyrene-1-yl-ethyl)-ammonium bromide (4) (solubilization behavior observed by using 4 was described briefly in reference 4a). Transmission electron microscopy (TEM), as well as visible/near-IR, fluorescence, and near-IR photoluminescence spectroscopies were employed to reveal the solubilization properties of 4 in water, and to compare these results with those obtained by using sodium dodecyl sulfate (SDS) and hexadecyltrimethylammonium bromide (HTAB) as solubilizers. Compound 4 solubilized both the as-produced SWNTs (raw-SWNTs) and purified SWNTs under mild experimental conditions, and the solubilization ability was better than that of SDS and HTAB. Near-IR photoluminescence measurements revealed that the chiral indices of the SWNTs dissolved in an aqueous solution of 4 were quite different from those obtained by using micelles of SDS and HTAB; for a SWNTs/4 solution, the intensity of the (7,6), (9,5), and (12,1) indices were strong and the chirality distribution was narrower than those of the micellar solutions. This indicates that the aqueous solution of 4 has a tendency to dissolve semiconducting SWNTs with diameters in the range of 0.89-1.0 nm, which are larger than those SWNTs (0.76-0.97 nm) dissolved in the aqueous micelles of SDS and HTAB.     

Alkyl Chain Length- and Polymorph-Dependent Photomechanochromic Fluorescence of Anthracene Photodimerization in Molecular Crystals: Role of the Lattice Stiffness

Anthracene–pentiptycene hybrid systems 1-Cn , where n refers to the number of carbon atoms in the linear alkyl chain, crystallize in three different polymorphs, denoted Y (yellow), G (green), and B (blue) forms in terms of the fluorescence color. While all Y-form crystals show the same yellow-to-blue fluorescence color response to the photomechanical stress generated by the anthracene [4+4] photodimerization reaction, the four G forms exhibit distinct photomechanofluorochromism (PMFC): from green to blue for G-1-C4 , to orange for G-1-C7 , to red for G-1-C8 , and to red then blue for G-1-C9 , and the B forms show no photochromic activity. The intriguing RGB three-color PMFC and abnormal topochemical reactivity of G-1-C9 are attributed to inherent softness of the crystal lattice.     

Exciton Coupling of Surface Complexes on a Nanocrystal Surface

Exciton coupling may arise when chromophores are brought into close spatial proximity. Herein the intra‐nanocrystal exciton coupling of the surface complexes formed by coordination of 8‐hydroxyquinoline to ZnS nanocrystals (NCs) is reported. It is studied by absorption, photoluminescence (PL), PL excitation (PLE), and PL lifetime measurements. The exciton coupling of the surface complexes tunes the PL color and broadens the absorption and PLE windows of the NCs, and thus is a potential strategy for improving the light‐harvesting efficiency of NC solar cells and photocatalysts.     

Comparison of the Solution Luminescence Properties and Solid-Matrix Luminescence Properties of 2-Amino-1-Methyl-6-Phenylimidazo[4,5-B]Pyridine

Abstract

The solution fluorescence properties of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) were compared with the solid-matrix luminescence properties of PhIP. The fluorescence properties were obtained in ethanol and several binary solutions of ethanol:water. An ethanol solution of PhIP gave a very strong fluorescence signal and the ethanol:water solutions only showed a small increase in the fluorescence signal. Acidic solutions of PhIP in ethanol:water (7:3) showed a major decrease in fluorescence intensity with at HCl of 10^?4 M and greater, but NaOH solutions of PhIP did not affect the fluorescence intensity to any great extent. Both acidic and basic solutions gave fluorescence emission spectra that were shifted to longer wavelengths. Solid-matrix room-temperature fluorescence (SMRTF) and solid-matrix room-temperature phosphorescence (SMRTP) were readily obtained on filter paper. SMRTP showed some distinct advantages over SMRTF and gave a limit of detection of 0.2 ng on filter paper. Several aspects of both solution luminescence and solid-matrix luminescence of PhIP are discussed.     

Solid-State NMR Study of Phase Separation and Order of Water Molecules and Silanol Groups in Polysiloxane Networks

Homogeneity and structure of organically modified polysiloxane networks prepared by sol-gel co-condensation, as well as location and nature of water molecules and silanol groups were studied by 1D and 2D solid-state NMR. ¹H–²⁹Si and ¹H–¹H interatomic distances were estimated from variable contact-time CP/MAS experiments, ¹H NMR chemical shifts and off-resonance WISE NMR. A structure model of these networks is proposed and discussed. The fraction of proton-inaccessible units Q⁴ in the networks decreases with increasing amounts of dimethylsiloxane (D) and methylsiloxane (T) units. In contrast to systems prepared by co-condensation of tetraethoxysilane (TEOS) with dimethyl(diethoxy)silane (DMDEOS), proton-inaccessible units form essential fraction in networks prepared by co-condensation of TEOS with methyl(triethoxy)silane (MTEOS). The proton-accessible part of the networks with high O/Si ratios is nano-heterogeneous phase, which is composed of water containing Q ⁱ particles separated by copolymer domains. The overall homogeneity and uniformity of binding sites around silanol groups increases by co-condensation TEOS with DMDEOS or MTEOS, while the amount of physisorbed water as well as the hydrogen bond strength decreases, as compared with neat silica gel prepared by polycondensation of TEOS.     

Shedding Light on the Diverse Reactivity of NacNacAl with N‐Heterocycles

The aluminum(I) compound NacNacAl (NacNac=[ArNC(Me)CHC(Me)NAr]^?, Ar=2,6‐iPr₂C₆H₃, 1 ) shows diverse and substrate‐controlled reactivity in reactions with N‐heterocycles. 4‐Dimethylaminopyridine (DMAP), a basic substrate in which the 4‐position is blocked, induces rearrangement of NacNacAl by shifting a hydrogen atom from the methyl group of the NacNac backbone to the aluminum center. In contrast, C?H activation of the methyl group of 4‐picoline takes place to produce a species with a reactive terminal methylene. Reaction of 1 with 3,5‐lutidine results in the first example of an uncatalyzed, room‐temperature cleavage of an sp² C?H bond (in the 4‐position) by an Al^I species. Another reactivity mode was observed for quinoline, which undergoes 2,2′‐coupling. Finally, the reaction of 1 with phthalazine produces the product of N?N bond cleavage.     

Ultrasensitive Biosensing Platform Based on the Luminescence Quenching Ability of Plasmonic Palladium Nanoparticles

An ultrasensitive biosensing platform for DNA and protein detection is constructed based on the luminescence quenching ability of plasmonic palladium nanoparticles (PdNPs). By growing the particles into large sizes (ca. 30 nm), the plasmonic light absorption of PdNPs is broadened and extended to the visible range with extinction coefficients as high as 10⁹ L mol^?1 cm^?1, enabling complete quenching of fluorescent dyes that emit at diverse ranges and that are tagged to bioprobes. Meanwhile the nonspecific quenching of the dyes (not bound to probes) is negligible, leading to extremely low background signal. Utilizing the affinity of PdNPs towards bioprobes, such as single‐stranded (ss) DNA and polypeptide molecules, which is mainly assigned to the coordination interaction, nucleic acid assays with a quantification limit of 3 pM target DNA and protein assay are achieved with a simple mix‐and‐detect strategy based on the luminescence quenching‐and‐recovery protocol. This is the first demonstration of biosensing employing plasmonic absorption of nanopalladium, which offers pronounced sensing performances and can be reasonably expected for wide applications.     

Quantifying the Tunable Conjugated Area of Graphene Oxide by Using Pyrene as a Fluorescent Probe

The determination of oxygenous groups, conjugated area ratio, and reduction efficiency of graphene oxide (GO) is a difficult task because of its heterogeneous structure. Herein, a novel approach is described for a detailed understanding of the surface chemistry of GO by using pyrene as a fluorescent probe through π–π stacking interactions.