5,6,12,13‐Tetraazaperopyrenes as Unique Photonic and Mechanochromic Fluorophores

5,6,12,13‐Tetraazaperopyrenes with different number of tert‐butyl groups (c‐TAPP‐T, c‐TAPP‐H) were synthesized, via four‐fold Bischler–Napieralski cyclization as the key step. As deduced from the single‐crystal structures and optical properties, N‐doping and substitution type allow for a precise control of intermolecular interactions. Compared to the reported 1,3,8,10‐tetraazaperopyrenes, significantly different packing modes were found in 5,6,12,13‐tetraazaperopyrenes. Going from c‐TAPP‐T to c‐TAPP‐H, two additional tert‐butyl groups lead to different preferential growth directions, affording 1D and 2D microcrystals, respectively. Most importantly, both microcrystals exhibit excellent optical waveguide properties with extraordinarily low loss coefficients and unique polarization features. Although c‐TAPP‐H possesses a rigid and planar core, its crystals display an exceptional mechanochromic fluorescence, which, again, depends on the mode of molecular packing.     

Microcrystals of polydiacetylene derivatives and their linear and nonlinear optical properties

Organic microcrystals which are expected to have interesting and fascinating physical properties were fabricated by a reprecipitation method as aqueous dispersions. Many kinds of organic compounds have been microcrystallized by this convenient method. The size control has been extensively investigated for a polydiacetylene and succeeded in the range from several tens of nanometers to several micrometers by adjusting the temperature and concentration. Linear optical properties of these well-defined polydiacetylene microcrystals have been investigated and interesting size and temperature dependences of excitonic absorption are demonstrated. Nonlinear optical (NLO) properties of polydiacetylene microcrystals have also been evaluated by means of a Z-scan technique, and an extremely high nonlinear refractive index at the resonant wavelength was shown.     

Cu_2O微纳晶可控合成及其光催化性能研究——推荐一个综合化学实验

介绍一个综合化学实验——Cu2O微纳晶可控合成及其光催化性能研究。采用简单配合物作为前驱物,在水热条件下通过调节反应条件,合成多种形貌的Cu2O微纳晶体,并对所得的不同产品结构、形貌和光学性质进行表征,对其光催化能力作对比性研究。     

Growth of dumbbell-like ZnO microcrystals under mild conditions and their photoluminescence properties

Large-scale uniform dumbbell-like ZnO microcrystals were successfully synthesized via a facile solution method under mild conditions. The as-prepared dumbbells, with lengths of 3.5-5.4 microm and diameters of 1.3-1.8 microm, possess a single-crystal hexagonal structure and grow along the [0001] direction. The influence of the reactant concentration on the size and shapes of the ZnO samples had been studied, and the results revealed that the reactant concentration plays a crucial role in determining final morphologies of the samples. Moreover, the evolution process of the dumbbell-like ZnO microcrystals was viewed by field-emission scanning electron microscopy (FE-SEM) characterization, and a possible formation mechanism was proposed. In addition, optical properties of the ZnO samples prepared at different reaction times were also investigated by photoluminescence (PL) spectroscopy. The room-temperature PL spectrum of the dumbbell-like ZnO microcrystals shows a strong UV emission peak. The UV emission is further identified to originate from the radiative free-exciton recombination by the temperature-dependent PL.     

以苯甘氨酸基为侧链的光学活性甲基丙烯酰胺聚合物的合成及手性识别能力

合成了N-[(R)-α-叔丁氧基羰基苄基]甲基丙烯酰胺((R)-BCBMAM),通过自由基聚合法获得相应的光学活性聚合物(P(R-BCBMAM)),并以三氟乙酸为水解催化剂除去叔丁基而得到(P(R-CBMAM)).用1H-NMR,IR,CD和GPC对聚合物进行了结构表征,发现聚合溶剂和聚合物分子量对所得聚合物P(R-BCBMAM)的光学活性没有明显影响,P(R-BCBMAM)水解后光学活性有较大的改变.与单体相比,聚合物的比旋光度有较大的区别,且在对应于其侧基的紫外吸收处呈现明显不同于单体的Cotton效应,说明聚合物的主链可能形成了一定的二级结构.以P(R-BCBMAM)和P(R-CBMAM)制备的2种涂敷型高效液相色谱用手性固定相,对部分对映体具有一定的手性拆分能力.利用1H-NMR技术研究了上述2种聚合物与1,1'-联-2-萘酚(BINOL)的相互作用,它们对BINOL都具有良好的手性识别能力.     

Strong optical nonlinearities of self-assembled polymorphic microstructures of phenylethynyl functionalized fluorenones

The polymorphs of a phenylethynyl functionalized fluorenone derivative, and their controlled self-assembly for microstructures with different morphologies have been studied. These polymorphic microcrystals exhibit very distinctive NLO properties, which are highly correlated to their electronic and supramolecular structures.     

2D Organic Photonics: An Asymmetric Optical Waveguide in Self‐Assembled Halogen‐Bonded Cocrystals

Anisotropic organic molecular construction and packing are crucial for the optoelectronic properties of organic crystals. Two‐dimensional (2D) organic crystals with regular morphology and good photon confinement are potentially suitable for a chip‐scale planar photonics system. Herein, through the bottom‐up process, 2D halogen‐bonded DPEpe‐F₄DIB cocrystals were fabricated that exhibit an asymmetric optical waveguide with the optical‐loss coefficients of R_Backward=0.0346 dB μm^?1 and R_Forward=0.0894 dB μm^?1 along the [010] crystal direction, which can be attributed to the unidirectional total internal reflection caused by the anisotropic molecular packing mode. Based on this crystal direction‐oriented asymmetric photon transport, these as‐prepared 2D cocrystals have been demonstrated as a microscale optical logic gate with multiple input/out channels, which will offer potential applications as the 2D optical component for the integrated organic photonics.     

Stabilization of organic field-effect transistors by tert-butyl groups in dibenzotetrathiafulvalene derivatives

For a material for organic thin-film transistors, not only high mobility but also low threshold voltage and long-term stability are important requirements. In order to realize these properties, materials with relatively large oxidation potentials, namely weak donors, have been designed as p-channel organic semiconductors. Here we propose a different strategy; transistor properties of dibenzotetrathiafulvalene (DBTTF) are significantly improved by the introduction of tert-butyl groups. Although this chemical modification does not much change the ionization potential, small threshold voltage and stability over several months are attained together with the improved mobility, probably due to some kind of passivation effect of the bulky tert-butyl groups. In contrast, the systematic fluorine substitution rapidly diminishes the transistor performance. There are two kinds of herringbone structures with much different dihedral angles of about 50° and 130°, and the tert-butyl compound falls into the former category.     

Relationship Between Molecular Structure,Single crystal Packing and Self-Assembly Behavior: A Case Based on Pyrene Imide Derivatives

Development of new n-type one-dimensional (1D) self-assembly nanostructure and a clear understanding of the relationship between molecular structure and self-assembly behavior are important prerequisites for further designing and optimizing organic optoelectronic nanodevice. In this article, a series of n-type organic semiconductor materials based on pyrene imide were successfully synthesized through [4+2] cycloaddition reactions and their preliminary optical and electrochemical properties were studied. The simulated HOMO-LUMO bandgaps via DFT tallied with the experimental data well. The self-assembly of these materials showed needle or fiber-like morphologies, indicating that different conjugation degree or alkyl group had significant influence on their self-assembly behaviors. Furthermore, the single-crystal packing for these molecules were analyzed and it was found out that the changes of conjugated backbone and functional group would affect certain crystal lattice parameter significantly, such as the intermolecular packing distance and crystal size etc, which would further result in different self-assembly morphology.     

卤化银乳剂微晶体的结构与性能研究——Ⅶ.切角立方体核壳乳剂的壳厚对于微晶体的光吸收及其电性质影响

应用双注法制备了一系列不同外壳厚度和核壳比分别为1.2.3.4的切角立方体乳剂。用光镜和图象处理方法测定了颗粒大小及其分布,用紫外光度法测定了它们的光吸收,用介电损耗法测定了离子电导率,用微波光导法测定了光电导和光电子寿命。对本系列的核壳乳剂的外壳厚度对上述各种光物理性质以及感光性能的影响进行了讨论,发现最合适的外壳层的厚度与卤化银乳剂微晶体的双电层的厚度(即所谓的Debye长度)大致相当。     

Silver metal nanosized particles: Control of particle size,self assemblies in 2D and 3D superlattices and optical properties

Water in oil droplets are used to control the size of silver metal nanoparticles. After synthesis, the silver metal particles are extracted from reverse micelles and redispersed in a non polar solvent. By increasing the size of the water droplets the average size of silver nanoparticles increases from 2 nm to 7 nm with a rather high size distribution. To narrow the panicle distribution a size selected precipitation method is used. By deposition of a dilute solution containing the coated particles on a carbon grid, the particles arrange themselves in a monolayer organized in a hexagonal network. At high particle concentration, the particles are organized in multilayers forming microcrystals arranged in a face centered cubic structure. The optical properties of the silver nanoparticles isolated in micellar solution or self-assembled in 2D or 3D supperlattices are reported.     

简捷微波法制备麦穗状氧化锌微晶及其光学性能

以硝酸锌和三乙胺的水溶液为前驱体溶液,在回流条件下微波辐照5min,制得了麦穗状半导体ZnO微晶.采用XRD、SEM、EDS、UV-Vis和光致发光(PL)光谱对产品的晶体结构、形貌和光学性能进行表征.结果表明,ZnO微晶为六方纤锌矿结构,单个微晶呈麦穗状,是由大量麦粒样的纳米颗粒接种于微米棒表面构成的复合结构.UV-...     

Solvent‐Induced Structural Transition of Self‐Assembled Dipeptide: From Organogels to Microcrystals

Organogels that are self‐assembled from simple peptide molecules are an interesting class of nano‐ and mesoscale soft matter with simplicity and functionality. Investigating the precise roles of the organic solvents and their effects on stabilization of the formed organogel is an important topic for the development of low‐molecular‐weight gelators. We report the structural transition of an organogel self‐assembled from a single dipeptide building block, diphenylalanine (L ‐Phe‐L ‐Phe, FF), in toluene into a flower‐like microcrystal merely by introducing ethanol as a co‐solvent; this provides deeper insights into the phase transition between mesostable gels and thermodynamically stable microcrystals. Multiple characterization techniques were used to reveal the transitions. The results indicate that there are different molecular‐packing modes formed in the gels and in the microcrystals. Further studies show that the co‐solvent, ethanol, which has a higher polarity than toluene, might be involved in the formation of hydrogen bonds during molecular self‐assembly of the dipeptide in mixed solvents, thus leading to the transition of organogels into microcrystals. The structural transformation modulated by the co‐solvent might have a potential implication in controllable molecular self‐assembly.     

Correlating Photophysical Properties with Stereochemical Expression of 6s2 Lone Pairs in Two-dimensional Lead Halide Perovskites

Two-dimensional (2D) lead halide perovskites (LHPs) have shown great promises for light-emitting applications and excitonic devices. Fulfilling these promises demands an in-depth understanding on the relationships between the structural dynamics and exciton-phonon interactions that govern the optical properties. Here, we unveil the structural dynamics of 2D lead iodide perovskites with different spacer cations. Loose packing of an undersized spacer cation leads to out-of-plane octahedral tilting, whereas compact packing of an oversized spacer cation stretches Pb−I bond length, resulting in Pb²⁺ off-center displacement driven by stereochemical expression of the Pb²⁺ 6s² lone pair electrons. Density functional theory calculations indicate that the Pb²⁺ cation is off-center displaced mainly along the direction where the octahedra are stretched the most by the spacer cation. We find dynamic structural distortions associated with either octahedral tilting or Pb²⁺ off-centering lead to a broad Raman central peak background and phonon softening, which increase the non-radiative recombination loss via exciton-phonon interactions and quench the photoluminescence intensity. The correlations between the structural, phonon, and optical properties are further confirmed by the pressure tuning of the 2D LHPs. Our results demonstrate that minimizing the dynamic structural distortions via a judicious selection of the spacer cations is essential to realize high luminescence properties in 2D LHPs.     

Liquid-crystalline symmetric triblock copolymers

Symmetric fully liquid-crystalline triblock copolymers of various structures containing optically active mesogenic groups are for the first time synthesized via pseudoliving radical reversible addition-fragmentation chain-transfer polymerization. Their phase behavior and physicochemical and optical properties are studied. It is shown that, depending on composition, at low temperatures block copolymers can form at temperatures phase-separated structures caused by microsegregation of blocks of different chemical natures and that, with an increase in temperature, these structures can mix to form a cholesteric mesophase characterized by a helical supramolecular structure. A model illustrating the molecular packing of block copolymers with a phase-separated lamellar structure is advanced. The effect of the molecular structure of the block copolymers on their optical properties is discussed.     

A comparison of linear optical properties and redox properties in chalcogenopyrylium dyes bearing ortho-substituted aryl substituents and tert-butyl substituents

A series of thiapyrylium pentamethine dyes (4 and 12-15) bearing 2,2'-di-tert-butyl-6,6'-diphenyl, 2,2'-di-tert-butyl-6,6'-bis(2,6-dimethylphenyl), 2,2'-di-tert-butyl-6,6'-bis(2-methylphenyl), 2,2',6,6'-tetrakis(2,6-dimethylphenyl), and 2,2',6,6'-tetrakis(2-methylphenyl) substituents, respectively, were prepared and their linear optical properties and electrochemical redox properties were measured and compared to thiapyrylium pentamethine dyes 3 and 5. The tert-butyl and 2,6-dimethylphenyl substituents give nearly identical chromophores with respect to values of lambda(max), molar extinction coefficients (epsilon), bandwidths at half-height (nu(1/2)), and lack of absorption in the visible spectrum. The 2-methylphenyl substituent imparts linear optical properties that are intermediate between those of the tert-butyl and phenyl substituents. The 2,6-dimethylphenyl and 2-methylphenyl substituents impart greater oxidative stability based on anodic shifts in oxidation potential.     

Peptide-modified inverted colloidal crystal scaffolds with bone marrow stromal cells in the treatment for spinal cord injury

Carboxyl groups of surface-tethered poly(acrylic acid) (PAA) brushes should be able to serve as versatile moieties for a wide range of chemical modifications, including an attachment of bioactive species that can act as sensing probes for biosensors. In this research, poly(tert-butyl acrylate) (Pt-BA) brushes were prepared by surface-initiated atom transfer radical polymerization of tert-butyl acrylate. PAA brushes were then obtained after removal of the tert-butyl groups from the Pt-BA brushes by acid hydrolysis. The carboxyl group density of the PAA brushes can be varied as a function of chain length or molecular weight. The reactivity of the carboxyl groups of PAA brushes towards the immobilization of biotin, a frequently used model bioactive probe in biosensing applications, was evaluated. Qualitative determination of streptavidin (SA) binding to the biotin-attached PAA brushes was verified by fluorescence microscopy. The efficiency of the PAA brushes to act as a three dimensional (3D) precursor layer for biosensing applications was further demonstrated using surface plasmon resonance (SPR), where the biotin-attached PAA brushes showed an enhanced signal for the biospecific binding of SA in comparison with a self-assembled monolayer (SAM) of a carboxyl-terminated alkanethiol, used as a model two-dimensional (2D) conventional precursor layer. The PAA brushes showed very low non-specific interactions with two other tested proteins of a similar pI but different sizes. This desirable feature should be highly beneficial for the development of biosensors.     

Guest-host colloid crystals: experimental study and simulations

Disorder in colloid crystals was induced by doping them with a different number of large or small guest particles, which had a different deviation in size from the host colloids. The change in optical properties of the guest-host colloid crystals was assessed by using optical transmission spectroscopy while the variation in crystal structure was examined using scanning electron microscopy (SEM). The disruption in the crystalline lattices depended on the relative deviation in sizes of the guest and host particles and the concentration of the guest colloids. In parallel with experiments, the packing of spheres in guest-host crystals was modeled with a simulated annealing algorithm. A good correlation was found between the changes in crystal structure observed by SEM imaging and the simulated sphere packing. The experimental and simulated changes in the transmission spectra of guest-host colloid crystals were in good agreement.     

1,4-二氰基萘一维亚微米结构材料的制备及光学性能

用再沉淀法制备了1,4-二氰基萘（DCN）一维亚微米结构。通过改变制备条件分别得到了DCN的线状及管状一维结构。所制备的有机亚微米材料具有良好的结晶性,不同结构的生长取向存在一定的差别。由于DCN分子的有序堆积,亚微米结构的的发光比溶液的发光有一定的红移。通过对单根材料的表征发现,DCN亚微米结构具有良好的光波导性能。空心结构的光波导性能要明显优于实心结构,主要原因在于空气介质减小了光学损耗。     

Dendrimer-tuned formation of fluorescent organic microcrystals. Influence of dye hydrophobicity and dendrimer charge

The reprecipitation method is a simple and useful way to prepare microcrystals through a solvent exchange process. It was applied to three fluorescent dyes of the 4-amino-7-nitrobenz-2-oxa-1,3-diazole series. Compounds 1, 2, and 3 differ by the length of the alkyl chain, which comprises 8, 12, and 18 carbon atoms, respectively. The reprecipitation process was first studied in water, in the absence of additives. The kinetics was monitored by UV/vis absorption spectroscopy. The size and shape of the microparticles were analyzed by fluorescence microscopy and transmission electron microscopy. Dyes 1 and 2 lead to microcrystals, the whole process taking much more time for 2 than for 1. The long-chained dye 3 only gave stable aggregates. Therefore, it appears that the hydrophobicity of the organic dye markedly influenced the reprecipitation process. The latter was then studied in the presence of additives. Poly(amidoamine) dendrimers, terminated by 64 carboxylate or amino groups were placed in the reprecipitation medium. They had little effect upon the formation of aggregates for dye 3. In contrast, they drastically accelerated the reprecipitation of 1 and 2 and tuned the size and shape of the microcrystals. Platelets and spindles were thus obtained by varying the nature of the dendrimer, and their optical properties were briefly investigated.