High‐Generation Second‐Order Nonlinear Optical (NLO) Dendrimers that Contain Isolation Chromophores: Convenient Synthesis by Using Click Chemistry and their Increased NLO Effects

Herein, high‐generation dendrimers G4‐NS and G5‐NS , which contained 30 and 62 azo‐benzene chromophore moieties, respectively, were conveniently prepared in high purity and satisfied yields by a combination of divergent and convergent approaches, coupled with the utilization of the powerful Sharpless click reaction. These dendrimers possessed a regular structure of alternating layers of nitro‐based and sulfonyl‐based azo chromophores in which the sulfonyl‐based azo‐chromophore moieties were utilized as co‐isolation groups for the nitro‐based moieties to achieve larger macroscopic second‐order nonlinear optical (NLO) effects. These high‐generation dendrimers ( G4‐NS and G5‐NS ) displayed very large NLO efficiencies (up to 253.0 pm V^?1), which is, to the best of our knowledge, the record highest efficiency for simple azo‐chromophore moieties.     

The Utilization of Isolation Chromophore in an “A3+B2” Type Second‐Order Nonlinear Optical Hyperbranched Polymer

In this paper, a new nonlinear optical (NLO) hyperbranched polymer P1 is designed and synthesized successfully through one‐pot “A₃+B₂” approach via a simple Sonogashira coupling reaction, in which isolation chromophore is introduced to improve its comprehensive performance such as NLO activity, optical transparency, and stability. For comparison, its analogs, P2 and P3 , just containing one type of chromophore, are also prepared. Although P1 cannot be well poled under our test conditions, its NLO coefficient is still much higher than its analogs P2 , P3, and the linear polyaryleneethynylene P4 , which also contains isolation chromophore, indicating the advantages of isolation chromophore and the three‐dimensional (3D) spatial isolation from the highly branched structure in the NLO field.

     

From Nitro‐ to Sulfonyl‐Based Chromophores: Improvement of the Comprehensive Performance of Nonlinear Optical Dendrimers

Through the combination of the divergent and convergent approaches, coupled with the utilization of the powerful Sharpless “click‐chemistry” reaction, two series of sulfonyl‐based high‐generation NLO dendrimers were conveniently prepared with high purity and in satisfactory yields. Thanks to the perfect three‐dimensional (3D) spatial isolation from the highly branched structure and the isolation effect of the exterior benzene moieties and the interior triazole rings, these dendrimers exhibited large second harmonic generation coefficient (d₃₃) values up to 181 pm V^?1, which, to the best of our knowledge, is the highest value so far for polymers containing sulfonyl‐based chromophore moieties. Meanwhile, compared with the nitro‐chromophore‐based analogues, their optical transparency and NLO stability were improved in a large degree, due to the lower dipole moment (μ) and the special main‐chain structure of sulfonyl‐based chromophore in these dendrimers.     

Second‐Order Nonlinear Optical Activity of Dipolar Chromophores Based on Pyrrole‐Hydrazono Donor Moieties

Donor1+donor2→acceptor : The second‐order NLO molecular properties of a class of dipolar chromophores that incorporate the following design elements are investigated: 1) a substituted hydrazono moiety as a strong donor; 2) a pyrrole ring as an auxiliary donor; 3) strong acceptor groups (see figure). Their first hyperpolarisabilities show good promise for use in electro‐optical devices.

     

Second‐Order Nonlinear Optical Properties of a Dithienylethene–Indolinooxazolidine Hybrid: A Joint Experimental and Theoretical Investigation

The nonlinear optical (NLO) properties of a double photochrome molecular switch are reported for the first time by considering the four trans forms of a dithienylethene–indolinooxazolidine hybrid. The four forms are characterized by means of hyper‐Rayleigh scattering (HRS) experiments and quantum chemical calculations. Experimental measurements provide evidence that the pH‐ and light‐triggered transformations between the different forms of the hybrid are accompanied by large variations of the first hyperpolarizability, which makes this compound an effective multistate NLO switch. Quantum chemical calculations conducted at the time‐dependent Hartree–Fock and time‐dependent DFT levels agree with the experimental data and allow a complete rationalization of the NLO responses of the different forms. The HRS signal of the forms with an open indolinooxazolidine moiety are more than one order of magnitude larger than that measured for the other forms, whereas the open/closed status of the dithienylethene subunit barely influences the dynamic NLO properties. However, extrapolation of the NLO responses to the static limit leads to univocally distinguishable intrinsic responses for three of the various forms. This hybrid system thus acts as a highly efficient multistate NLO switch for eventual exploitation in optical memory systems with multiple storage and nondestructive readout capacity.     

Tuning the Dipolar Second‐Order Nonlinear Optical Properties of Cyclometalated Platinum(II) Complexes with Tridentate N^C^N Binding Ligands

Appropriate functionalization of the cyclometalated ligand, L , and the choice of the ancillary ligand, X, allows the dipolar second‐order nonlinear optical response of luminescent [Pt L X] complexes—in which L is an N^C^N‐coordinated 1,3‐di(2‐pyridyl)benzene ligand and X is a monodentate halide or acetylide ligand—to be controlled. The complementary use of electric‐field‐induced second‐harmonic (EFISH) generation and harmonic light scattering (HLS) measurements demonstrates how the quadratic hyperpolarizability of this appealing family of multifunctional chromophores, characterized by a good transparency throughout much of the visible region, is dominated by an octupolar contribution.     

DNA‐Based Polymers as Chiral Templates for Second‐Order Nonlinear Optical Materials

The unique symmetry properties of chiral systems allow the emergence of coherent second harmonic generation in polymeric materials lacking polar order. Deoxyribonucleic acid (DNA) treated with the surfactant cetyltrimethylammonium (CTMA) was drop‐cast to spontaneously form films that are active for coherent second harmonic generation (SHG). SHG images acquired as a function of incident and exigent polarization are in good agreement with theoretical predictions assuming nonpolar D_∞ symmetry for the double‐stranded DNA chains. Doping the DNA films with crystal violet substantially increases the efficiency of SHG, but does not significantly alter the polarization‐dependence, suggesting that the SHG generated upon doping arises from the same chiral‐specific origin, presumably templated by the DNA. These results raise the possibility of new design strategies for organic nonlinear optical materials based on soft chiral polymers that do not require polar order.     

Dendronized Polymers with High FTC-chromophore Loading Density:Large Second-order Nonlinear Optical Effects,Good Temporal and Thermal Stability

In this study,two new dendronized nonlinear optical(NLO)polymers were synthesized with high FTC chromophore loading density by introduction of high generation chromophore dendrons on the side chains.Due to their suitable molecular weights,both of them possessed good solubility in common solvents.They also inherited the advantages of dendrimers(large NLO coefficient),especially for PG2 whose NLO coefficient d33 value was as high as 282 pm·V^–1.Also,PG2 had a good temporal stability with 80%of its maximum value being retained at the temperature as high as 129℃.     

The Role of Ion Pairs in the Second‐Order NLO Response of 4‐X‐1‐Methylpiridinium Salts

A series of 4‐X‐1‐methylpyridinium cationic nonlinear optical (NLO) chromophores (X=(E)‐CH?CHC₆H₅; (E)‐CH?CHC₆H₄‐4′‐C(CH₃)₃; (E)‐CH?CHC₆H₄‐4′‐N(CH₃)₂; (E)‐CH?CHC₆H₄‐4′‐N(C₄H₉)₂; (E,E)‐(CH?CH)₂C₆H₄‐4′‐N(CH₃)₂) with various organic (CF₃SO₃^?, p‐CH₃C₆H₄SO₃^?), inorganic (I^?, ClO₄^?, SCN^?, [Hg₂I₆]^2?) and organometallic (cis‐[Ir(CO)₂I₂]^?) counter anions are studied with the aim of investigating the role of ion pairing and of ionic dissociation or aggregation of ion pairs in controlling their second‐order NLO response in anhydrous chloroform solution. The combined use of electronic absorption spectra, conductimetric measurements and pulsed field gradient spin echo (PGSE) NMR experiments show that the second‐order NLO response, investigated by the electric‐field‐induced second harmonic generation (EFISH) technique, of the salts of the cationic NLO chromophores strongly depends upon the nature of the counter anion and concentration. The ion pairs are the major species at concentration around 10^?3 M , and their dipole moments were determined. Generally, below 5×10^?4 M , ion pairs start to dissociate into ions with parallel increase of the second‐order NLO response, due to the increased concentration of purely cationic NLO chromophores with improved NLO response. At concentration higher than 10^?3 M , some multipolar aggregates, probably of H type, are formed, with parallel slight decrease of the second‐order NLO response. Ion pairing is dependent upon the nature of the counter anion and on the electronic structure of the cationic NLO chromophore. It is very strong for the thiocyanate anion in particular and, albeit to a lesser extent, for the sulfonated anions. The latter show increased tendency to self‐aggregate.     

两个二阶非线性光学高分子的合成与性能：改善高分子光学非线性-透明性矛盾的尝试

通过后功能化反应将两个新的非线性光学发色团（1和2）分别作为侧链引入聚芳醚砜主链,得到两个新的非线性光学高分子（P1和P2）。这两个发色团（1和2）被设计为含有相同的电子给体（二烷基氨基）和相同的电子受体（TCF）,但含有不同长度的共轭桥,即2包含一个组合共轭桥（苯基二氮烯 + 苯乙烯）,而1的共轭桥要短得多（仅为苯乙烯）。研究了P1和P2的线性和非线性光学性质。与P1相比,P2在呈现出相近的非线性光学系数（d₃₃）的同时异乎寻常地达到了更好的光学透明性（最大吸收波长蓝移16 nm）。结果表明：组合共轭桥结构的引入对于在非线性光学高分子的非线性-透明性之间达到某种平衡起到了良好作用。     

Electron‐Transfer Photochromism To Switch Bulk Second‐Order Nonlinear Optical Properties with High Contrast

The first bulk electron‐transfer photochromic compound with intrinsic second‐order nonlinear optical (NLO) photoswitching properties has been synthesized. This system employs an electron‐transfer photoactive asymmetric viologen ligand coordinated to a zinc(II) center.     

Using Two Simple Methods of Ar?ArF Self‐Assembly and Isolation Chromophores to Further Improve the Comprehensive Performance of NLO Dendrimers

Herein, through a combination of divergent and convergent approaches, coupled with the utilization of the powerful Sharpless “click chemistry” reaction, two series of high‐generation nonlinear optical (NLO) dendrimers have been conveniently prepared in high purity and satisfactory yields. Perfluoroaromatic rings and isolation chromophores were introduced to further improve their comprehensive performance. Thanks to the effects of Ar? Ar^F self‐assembly and the isolation chromophores, coupled with perfect 3D spatial isolation from the highly branched structure of the dendrimer, G5‐PFPh‐NS displayed very large NLO efficiency (up to 257 pm V^?1), which is, to the best of our knowledge, the new record highest value reported so far for simple azo chromophore moieties. High‐quality wide optical transparency and good stability were also achieved.     

SnI4⋅(S8)2: A Novel Adduct‐Type Infrared Second‐Order Nonlinear Optical Crystal

A simple adduct from tin tetraiodide SnI₄ and octasulfur S₈, SnI₄?(S₈)₂ ( 1 ), is obtained employing a facile reaction. The combination of Sn⁴⁺ ions with d¹⁰ electron configuration, acentric SnI₄ tetrahedra, and lone‐pair effects of S₈, makes 1 a phase‐matchable infrared NLO crystal with a moderate second‐harmonic generation (SHG) response and a very high laser‐induced damage threshold (LIDT), which is well confirmed by the DFT calculations.     

Dendrimers based on [1,3,5]‐triazines

A comprehensive and chronological account of dendrimers based on [1,3,5]‐triazines is provided. Synthetic strategies to install the triazine through cycloaddition, cyclotrimerization, and nucleophilic aromatic substitution of cyanuric chloride are discussed. Motivations and applications of these architectures are surveyed, including the preparation of supramolecular assemblies in the solution and solid states and their use in medicines, advanced materials, and separations when anchored to solid supports. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3411–3433, 2006     

Synthesis,Photophysics and Nonlinear Optical Properties of Stilbenoid Pyrimidine‐Based Dyes Bearing Methylenepyran Donor Groups

The nonlinear properties and the photophysical behavior of two π‐conjugated chromophores that incorporate an electron‐deficient pyrimidine core (A) and γ‐methylenepyrans as terminal donor (D) groups have been thoroughly investigated. Both dipolar and quadrupolar branching strategies are explored and rationalized on the basis of the Frenkel exciton model. Even though a cooperative effect is clearly observed if the dimensionality is increased, the nonlinear optical (NLO) response of this series is moderate if one considers the nature of the D/A couple and the size of the chromophores (as measured by the number of π electrons). This effect was attributed to a disruption in the electronic conjugation within the dyes’ scaffold for which the geometry deviates from planarity owing to a noticeable twisting of the pyranylidene end‐groups. This latter structural parameter also has a strong influence on the excited‐state dynamics, which leads to a very efficient fluorescence quenching.     

Thermoresponsive Supramolecular Dendronized Polymers

Combining the concepts of supramolecular polymers and dendronized polymers provides the opportunity to create bulky polymers with easy structural modification and tunable properties. In the present work, a novel class of side‐chain supramolecular dendronized polymethacrylates is prepared through the host–guest interaction. The host is a linear polymethacrylate (as the backbone) attached in each repeat unit with a β‐cyclodextrin (β‐CD) moiety, and the guest is constituted with three‐fold branched oligoethylene glycol (OEG)‐based first‐ (G1) and second‐generation (G2) dendrons with an adamantyl group core. The host and guest interaction in aqueous solution leads to the formation of the supramolecular polymers, which is supported with ¹H NMR spectroscopy and dynamic light scattering measurements. The supramolecular formation was also examined at different host/guest ratios. The water solubility of hosts and guests increases upon supramolecular formation. The supramolecular polymers show good solubility in water at room temperature, but exhibit thermoresponsive behavior at elevated temperatures. Their thermoresponsiveness is thus investigated with UV/Vis and ¹H NMR spectroscopy, and compared with their counterparts formed from individual β‐CD and the OEG dendritic guest. The effect of polymer concentration and molar ratio of host/guest was examined. It is found that the polar interior of the supramolecules contribute significantly to the thermally‐induced phase transitions for the G1 polymer, but this effect is negligible for the G2 polymer. Based on the temperature‐varied proton NMR spectra, it is found that the host–guest complex starts to decompose during the aggregation process upon heating to its dehydration temperature, and this decomposition is enhanced with an increase of solution temperature.     

High‐Molar‐Mass,First and Second Generation L‐Lysine Dendronized Polymethacrylates

The first ( PG1 ) and second ( PG2 ) generation dendronized polymethacrylates with L ‐lysine based dendrons have been synthesized, and their conformation has been investigated. The chiral dendrons can be synthesized efficiently on a multi‐gram scale from L ‐lysine by a solution peptide coupling method, and the over‐all yields for the first ( MG1 ) and second ( MG2 ) generation macromonomers are 77 and 75%, respectively. High molar masses (1 to 2 million) of PG1 and PG2 are achieved by conventional radical polymerization of the corresponding macromonomers. Characterization with optical rotation, circular dichroism, and UV measurements showed that, in contrast to PG1 , PG2 adopts a single‐handed helical conformation in solution, which is stable in different polar solvents and also over a broad temperature range. Interestingly, the stable helical conformation remained in aqueous solution after deprotection of the terminal amines, by which the mass and steric hindrance of the dendrons reduced significantly.