A Photophysical Study of Terphenyl Core Oligosulfonimide Dendrimers Exhibiting High Steady‐State Anisotropy

The photophysical properties of three dendrimers containing a p‐terphenyl core with appended sulfonimide branches of different size and n‐octyl chains have been investigated in dichloromethane solution. In the dendrimer absorption spectra contributions from both the branches and the core are clearly identified. The fluorescence spectra show only the characteristic fluorescence of the terphenyl unit. Energy transfer from the appended chromophoric groups to the core does not occur. In the dendrimers, the terphenyl core exhibits a very high fluorescence quantum yield (ca. 0.75) and a short emission lifetime (0.8 ns). These properties allowed investigations of the fluorescence depolarization caused by rotation of the dendrimers. The dendrimers show a very high steady‐state anisotropy in dichloromethane solution at room temperature (0.24 for the largest one), compared to that of the parent terphenyl under the same experimental conditions (<0.01) and in rigid matrix (0.33). Both the n‐octyl chains and the sulfonimide branches play important roles to slow down the molecular rotation.     

Phenylacetylene Dendrimers Containing a Fluorene Core: Synthesis and Spectroscopic Studies

Phenylacetylene dendrimers 9 – 11 containing fluorene as the core with a larger HOMO‐LUMO energy gap were synthesized and characterized. Their structure and properties were studied by UV, FL, ¹H NMR, MS etc. These novel phenylacetylene dendrimers exhibit unique photophysical properties. They exist a new absorption band around 340 nm whose molar coefficient decreases with increasing generation. The band‐gaps of 9 – 11 are 3.54, 3.43 and 3.02 respectively. The fluorescence quantum yield of 10 is as high as 0.61.     

以卟啉为中心核的树枝状化合物

以卟啉基为中心核的树枝状化合物具有特殊的物理、化学及光电性能,其中一个重要特性是具有优良的能量和电子转移性能,近年来研究人员合成了一系列新型的以卟啉为中心核的树枝状化学物,这些化合物在许多领域有着潜在的应用前景。本文综述了近几年来以卟啉基为中心核的树枝状化合物的最新研究结果,介绍了一些具有代表性的新型化合物,概述了部分化合物的合成方法及性能,这些化合物由于其结构改变带来的性能变化,分别在光收集材料、发光材料、光动力学疗法、催化剂、传感器等领域有着潜在的应用前景。最后展望了此类化合物的发展方向。     

外围由小分子修饰的树枝状聚酰胺的合成及其荧光性能研究

合成了1－5代外围由小分子荧光体修饰的树枝状聚酰胺，通过红外，紫外，核磁等表征了其结构，并对其荧光性能进行了研究，修饰后的固体产物的荧光较修饰前粘稠体产物的荧光强得多，树枝状高分子荧光受组分比，代数，溶液浓度，溶剂等因素的影响，有机硅对树状高分子的端氨基与3，5二羟基苯甲酸按1／1摩尔比反应时，其产物荧光最强，对于端氨基与3，5－二羟基苯甲酸摩尔比为1／1的不同代树枝状聚酰胺而言，2代产物荧光最强。     

PAMAM修饰的六苯并蔻衍生物的合成及其光物理研究

设计合成了外围以0.5、1.5、2.5代聚酰胺-胺(PAMAM)树枝形聚合物修饰的六苯并蔻衍生物HBC-C₆-PAMAM-D_m(m=0.5, 1.5, 2.5), 化合物结构通过了¹HNMR、¹³CNMR、IR和MS的表征.测定了HBC-C₆-PAMAM-D_m在四氢呋喃、乙腈和二氯甲烷中的吸收和荧光发射光谱, 三种溶剂中不同代数的HBC-C₆-PAMAM-D_m均以聚集态形式存在,外围树枝形聚合物骨架与核心HBC发色团的振动耦合作用随代数增加而增强,导致HBC振动能级不均化,引起吸收和荧光光谱发生变化.     

Multifunctional Supramolecular Dendrimers with an s‐Triazine Ring as the Central Core: Liquid Crystalline,Fluorescence and Photoconductive Properties

Novel liquid crystal (LC) dendrimers have been synthesised by hydrogen bonding between an s‐triazine as the central core and three peripheral dendrons derived from bis(hydroxymethyl)propionic acid. Symmetric acid dendrons bearing achiral promesogenic units have been synthesised to obtain 3:1 complexes with triazine that exhibit LC properties. Asymmetric dendrons that combine the achiral promesogenic unit and an active moiety derived from coumarin or pyrene structures have been synthesised in order to obtain dendrimers with photophysical and electrochemical properties. The formation of the complexes was confirmed by IR and NMR spectroscopy data. The liquid crystalline properties were investigated by differential scanning calorimetry, polarising optical microscopy and X‐ray diffractometry. All complexes displayed mesogenic properties, which were smectic in the case of symmetric dendrons and their complexes and nematic in the case of asymmetric dendrons and their dendrimers. A supramolecular model for the lamellar mesophase, based mainly on X‐ray diffraction studies, is proposed. The electrochemical behaviour of dendritic complexes was investigated by cyclic voltammetry. The UV/Vis absorption and emission properties of the compounds and the photoconductive properties of the dendrons and dendrimers were also investigated     

Core Functionality and Scaling Behavior of Lysine Dendrimers

Summary: A scaling exponent to describe the dependence of the hydrodynamic radius as a characteristic length of the molecule on the molecular weight, has been determined for low generation dendrimers with a thiacalixarene core and lysine dendrons. The hydrodynamic radius has been calculated from the diffusion coefficient measured by pulsed‐field‐gradient NMR spectroscopy. Scaling exponents of 2.0 for the lysine monodendron, 2.3 for a dendrimer with a bifunctional core, and 3.9 for a dendrimer with a tetrafunctional core have been determined. For a given structure of the dendrons, the scaling exponent reflects the functionality of the core of the dendrimers.

Hydrodynamic radius of lysine dendrons as a function of molar mass.     

Bismuth Complexes in Phenylazomethine Dendrimers: Controllable Luminescence and Emission in the Solid State

Dendritic phosphors were obtained by the stepwise integration of BiCl₃ in phenylazomethine dendrimers. The bismuth‐coordinated phenylazomethines displayed photoluminescence at 500–800 nm, and the intensity could be tuned by changing the stoichiometry of BiCl₃ and the dendrimer. This phosphor did not show serious luminescence quenching even though the local concentration of BiCl₃ in the dendrimer was as high as 20 M , and luminescence was also observed in the solid state. The absorption and emission properties could be reversibly switched by addition of a Lewis base or under electrochemical redox control, which induced the reversible complexation of BiCl₃ in the dendrimer.     

Dendrimers as ligands: an investigation into the stability and kinetics of Zn2+ complexation by dendrimers with 1,4,8,11-tetraazacyclotetradecane (cyclam) cores

We have investigated the complexation of Zn(2+) with 1,4,8,11-tetrakis(naphthylmethyl) cyclam (1; cyclam=1,4,8,11-tetraazacyclotetradecane) and with two dendrimers consisting of a cyclam core with four dimethoxybenzene and eight naphthyl appendages (2), and twelve dimethoxybenzene and sixteen naphthyl appendages (3). An important, common feature of model compound 1 and dendrimers 2 and 3 is that their potentially fluorescent naphthyl units are quenched by exciplex formation with the cyclam nitrogen atoms. Complexation with Zn(2+), however, prevents exciplex formation and results in the appearance of an intense naphthyl fluorescence signal that can be used for monitoring the complexation process. Luminescence titration, together with competition experiments and (1)H NMR titration, have shown that 1:1 and 1:2 (metal/ligand) complexes are formed in the cases of 2 and 3, whereas model compound 1 gives only a 1:1 complex. We have also investigated the 1:1 complexation kinetics by the stopped-flow technique. In the case of 1, a second-order process (k(1)=44x10(5) M(-1) s(-1)) is followed by two consecutive first-order steps (k(2)=0.53 s(-1) and k(3)=0.10 s(-1)). For 2, a slower second-order process (k(1)=4.9x10(5) M(-1) s(-1)) is followed by a slow first-order step (k(2)=0.40 s(-1)). In the case of 3, only a very slow second-order process was observed (k(1)=1.2x10(5) M(-1) s(-1)). The different metal-ion incorporation rates for model compound 1 and dendrimers 2 and 3 have been discussed in terms of conformational changes of the dendron subunits affecting the chelating properties of the cyclam core. This work reports the first kinetic study on metal-ion coordination by dendrimers with a well-defined coordination site.     

Carbazole Dendrimers as Solution‐Processable Thermally Activated Delayed‐Fluorescence Materials

Recently, thermally activated delayed fluorescence (TADF) materials have received increasing attention as effective emitters for organic light‐emitting diodes (OLEDs). However, most of them are usually employed as dopants in a host material. In this report, carbazole dendrimers with a triphenyl‐s‐triazine core are reported, which are the first solution‐processable, non‐doped, high‐molecular‐weight TADF materials. The dendrimers were obtained by a new and facile synthetic route using the tert‐butyldimethylsilyl moiety as a protecting group. All dendrimers showed TADF in toluene. Measurements of the temperature‐dependent luminescence lifetime revealed that spin‐coated neat films also showed TADF with moderate quantum yields. OLED devices incorporating these dendrimers as spin‐coated emitting layers gave external quantum efficiencies of up to a 3.4 %, which suggests that this device is harvesting triplet excitons. This result indicates that carbazole dendrimers with attached acceptors are potential TADF materials owing to their polarized electronic structure (with HOMO–LUMO separation).     

具有分子识别功能的树状大分子

简单介绍了近年来高分子领域中十分活跃的树状大分子的应用进展，着重介绍了具有分子识别功能的树状大分子在萃取分离、增溶、识别肿瘤细胞……等方面的应用。引用文献34篇。     

Exciton Migration in Conjugated Dendrimers: A Joint Experimental and Theoretical Study

We report a joint experimental and theoretical investigation of exciton diffusion in phenyl‐cored thiophene dendrimers. Experimental exciton diffusion lengths of the dendrimers vary between 8 and 17 nm, increasing with the size of the dendrimer. A theoretical methodology is developed to estimate exciton diffusion lengths for conjugated small molecules in a simulated amorphous film. The theoretical approach exploits Fermi’s Golden Rule to estimate the energy transfer rates for a large ensemble of bimolecular complexes in random relative orientations. Utilization of Poisson’s equation in the evaluation of the Coulomb integral leads to very efficient calculation of excitonic couplings between the donor and the acceptor chromophores. Electronic coupling calculations with delocalized transition densities revealed efficient coupling pathways in the bulk of the material, but do not result in strong couplings between the chromophores which are calculated for more localized transition densities. The molecular structures of dendrimers seem to be playing a significant role in the magnitude of electronic coupling between chromophores. Simulated diffusion lengths correlate well with the experimental data. The chemical structure of the chromophore, the shape of the transition densities and the exciton lifetime are found to be the most important factors in determining the size of the exciton diffusion length in amorphous films of conjugated materials.     

丹磺酰基为核的树枝状化合物的合成和光谱性质研究

通过收敛法合成了二代丹磺酰基为核、活泼羟乙基为外围基团的新型树枝状化合物, 产物进行了IR, ¹H NMR, ¹³C NMR, MS, EA表征. 该合成方法无需复杂的官能团保护与去保护, 后处理简便, 产率高. 对产物的荧光光谱的初步研究结果表明, 随着树枝状产物代数的增加, 荧光强度得到成倍增强.     

激发态分子内质子转移(ESIPT)发色团修饰的树枝形聚合物合成及光物理研究

设计合成了0～4代外围修饰激发态分子内质子转移(ESIPT)发色团的聚酰胺-胺树枝形聚合物G0～G4,化合物结构经过IR,1H NMR,13C NMR和MS表征.稳态光谱研究表明,树枝形聚合物在四氢呋喃溶液中形成了聚集体,发色团酮式发光随着化合物代数增大呈先增加后减小的变化.质子化树枝形聚合物G1-H～G4-H能溶于水,并在水中形成20 nm左右的聚集体,发色团在聚集体疏水区中构象受限,仅发射酮式发光,并且发光强度受树枝形聚合物分子大小的影响.     

Synthesis,Structural Characterization,and Thermoresponsivity of Hybrid Supramolecular Dendrimers Bearing a Polyoxometalate Core

A series of cationic dendrons bearing triethylene glycol monomethyl ether terminal groups of different generations have been synthesized and used to encapsulate an inorganic polyanionic cluster [K_12.5Na_1.5(NaP₅W₃₀O₁₁₀)] through electrostatic interactions. The resulting dendritic cation–encapsulated polyoxometalate (POM) complexes, cluster–dendrimers, are soluble in water and exhibit lower critical solution temperatures (LCST). The thermoresponsivities of these complexes in aqueous solutions were studied by turbidimetry and variable‐temperature ¹H NMR spectroscopy. The observed cloud points show a remarkable dependence on the generation of the dendrons. Complexes composed of first‐generation dendrons exhibit no obvious thermoresponsive properties, but for complexes bearing second‐generation dendrons, the LCST decreases as the number of dendritic cations around the POM cluster increases. Complexes composed of third‐generation cations underwent reversible aggregation and disaggregation upon heating and cooling, respectively. This thermally induced self‐aggregation was characterized by DLS and TEM. In addition, the effects of salt and solvent on the LCST were investigated. This research demonstrates a new type of thermoresponsive dendritic organic–inorganic hybrid complex and provides a general route to the endowment of POMs with temperature‐sensitive properties through electrostatic interactions.     

Guest‐Induced Photophysical Property Switching of Artificial Light‐Harvesting Dendrimers

An artificial light‐harvesting multiporphyrin dendrimer ( 8P_ZnP_FB ) composed of a focal freebase porphyrin ( P_FB ) with eight zinc(II) porphyrin ( P_Zn ) wings exhibited unique photophysical property switching in response to specific guest molecule binding. UV/Vis titration studies indicated stable 1:2 host–guest complex formation between 8P_ZnP_FB and meso‐tetrakis(4‐pyridyl)‐porphyrin ( TPyP ) for which the first and second association constants were estimated to be >10⁸ M ^?1 and 3.0×10⁷ M ^?1, respectively. 8P_ZnP_FB originally shows 94 % energy transfer efficiency from P_Zn to the focal P_FB . By the formation of the host–guest complex ( 8P_ZnP_FB? 2 TPyP ) the emission intensity of 8P_ZnP_FB is significantly decreased, and an ultrafast charge separation state is generated. The energy transfer process from P_Zn wings to the P_FB core in 8P_ZnP_FB is almost entirely switched to an electron transfer process by the formation of 8P_ZnP_FB? 2 TPyP .     

Photophysical Methods for the Study of Sol-Gel Transition and Structure of Titania Gels

The sol to gel evolution of titania based systems in AOT (sodium 2-etil-hexil sulfosuccinate) reverse micelles is monitored by the fluorescence anisotropy of molecular probes located in the different phases of the system. In contrast with processes in homogeneous systems, hydrolysis and condensation reactions occur in different time windows. The obtained results allow to describe the location of the hydrolysis, the reorganisation of the surfactant and to predict the formation of precipitates.     

Aggregation‐Controlled Excimer Emission from Anthracene‐Containing Polyamidoamine Dendrimers

Lower generations of polyamidoamine (PAMAM) dendrimers were peripherally modified with anthracene moieties, and excimer emission from anthracene chromophores was investigated in an acetonitrile–water mixture at acidic and basic pH values. Results from fluorescence spectroscopic experiments suggest that 1) the propensity of anthracene‐modified PAMAM dendrimers to aggregate in acetonitrile is substantial in the presence of 15–20 vol % of water, and 2) aggregate formation in anthracene‐modified PAMAM dendrimers leads to unique morphologies in the ground state, where the anthracene units are pre‐arranged to form stable excimers upon photoexcitation. Three types of anthracene excimers are generated in the system, with face‐to‐face, angular, and T‐shaped geometry. The formation of different types of anthracene excimers was confirmed by steady‐state and time‐resolved fluorescence spectroscopic experiments. Experimental results further suggest that it is feasible to alter the type of excimer formed by anthracene units attached to the PAMAM dendrimers through altering the propensity for ground‐state aggregation. Most excitingly, increased π conjugation in the molecular framework of anthracene‐substituted PAMAM dendrimers leads to intense and exclusive excimer emission from anthracene at room temperature.