Using Two Simple Methods of ArArFSelf-Assembly and Isolation Chromophores to Further Improve the Comprehensive Performance of NLO Dendrimers

Exploring Favorable Supramolecular Interactions of Multifluorinated Aromatics in Dendronized Push-Pull Chromophores for Electro-Optics

Multifluorinated aromatics serve as supramolecular synthons in the research of organic electro-optic (EO) materials by exploiting π-π stacking interaction between the aromatic hydrocarbon and multifluorinated aromatic groups for performance improvement. However, non-classical hydrogen bonding remains largely unexplored in fluorinated EO dendrimers. In this study, three Fréchet-type generation 1 benzyl ether co-dendrons were synthesized by replacing one benzyl group with 2,3,5,6-tetrafluorobenzyl (p-HF4Bz), pentafluorobenzyl (C6F5Bz), and 2,3,4,5-tetrafluorobenzyl (o-HF4Bz) groups, to afford the benzoic acid derivatives D1, D2, and D3, which were further bonded to the donor and π-bridge moieties to afford three co-dendronized push-pull phenyltetraene chromophores EOD1, EOD2, and EOD3, respectively. The weak C-H⋅⋅⋅X (X=O, F) interactions in the crystal structure of D1 cumulatively add to the benzoic acid dimers to form an extended hydrogen-bonded network, while D2 is crystallized into a centric one-dimensional chain with strong intermolecular interactions. The poled films of EOD1 with PMMA exhibited the largest and most stable EO activity with optical homogeneity among the series. The results identify the effectiveness of weak but favorable hydrogen bonds enabled by the enhanced carbon acidity of p-HF4Bz synthon in D1, over the interactions in D2 and D3, for the rational design of supramolecular EO dendrimers.

Tetracyanobutadienyl-based Nonlinear Optical Dendronized Hyperbranched Polymer Synthesized via Facile [2+2] Cycloaddition Polymer Postfunctionalization

Dendronized hyperbranched polymers (DHPs) can provide advantages of both hyperbranched polymers and dendrimers, making them promising structure platform for high performance second-order nonlinear optical (NLO) materials. Herein, we report a new A₃ +B₂ -type DHP (HP2) through facile and efficient [2+2] cycloaddition polymer postfunctionalization, in which tetracyanobutadienyl-based moieties are introduced as the main chromophores while isophorone-bridged moieties serve as the isolation chromophores. Benefiting from this unique hyperbranched structure design, the measured d₃₃ value of HP2 can reach up to 96.6 pm/V with high thermal stability, making it a good material candidate for second-order NLO applications. This article is protected by copyright. All rights reserved.

Efficient Construction of Near-Infrared Absorption Donor-Acceptor Copolymers with and without Pt(II)-Incorporation toward Broadband Nonlinear Optical Materials

Organic nonlinear optical (NLO) materials have attracted immense scientific interest in various fields. Broadband NLO response extending to near-infrared (NIR) region is extremely important and remains challenging. Herein, two diketopyrrolopyrrole (DPP)-based donor-acceptor (D-A)-type π-conjugated copolymers with and without Pt(II) incorporation are rationally designed and synthesized toward broadband NLO response materials. The broad intramolecular charge transfer (ICT) absorption reaching 1000 nm due to the strong D-A interaction is well demonstrated by photophysical characterizations. The NLO properties of copolymers are studied using Z-scan technology. Owing to their extended π-conjugated D-A systems and near-infrared ICT absorption properties, both copolymers exhibit laser-induced NLO response to nanosecond as well as picosecond laser pulses upon the wavelengths of 532 and 1064 nm. Interestingly, introducing Pt(II) into the copolymer backbone can evidently improve the NLO property or unexpectedly switch the NLO response from saturable absorption to reverse saturable absorption. Meanwhile, both copolymers are successfully employed as optical limiting materials and exhibit broadband optical limiting abilities. Therefore, we present an efficient strategy toward broadband NLO materials, which may significantly facilitate the understanding of organic molecular structure-property relationship and promote their practical application.

Janus second-order nonlinear optical dendrimers: their controllable molecular topology and corresponding largely enhanced performance

A new type of Janus dendrimers, consisting of two different side dendrons with the dipole orientation of the second-order nonlinear optical (NLO) chromophore moieties partially in a non-centrosymmetric direction, was intelligently designed and synthesized in order to enhance the macroscopic NLO performance and break through the limitation of NLO efficiency in the current molecular topological structure of azo chromophore-based polymers. This kind of Janus dendritic structure was constructed by the combination of convergent and divergent methods, with the utilization of a powerful "click chemistry reaction". The obtained three dendrimers, D-13N, D-17N and D-21N, show very high NLO performance, especially the dramatically enhanced NLO coefficient of 299 pm V-1 for D-13N, which is the highest value ever reported for polymers containing a simple azo chromophore. The new dendrimers provide a clear structure-properties relationship between high NLO efficiency and the controllable molecular topology with the non-centrosymmetrical alignment of dipole orientation, thus opening up a new avenue for the further development of NLO dendrimers with high performance and more importantly providing some clues for the rational design of functional dendrimers with controllable molecular topology.

Recent advances in click chemistry applied to dendrimer synthesis

Dendrimers are monodisperse polymers grown in a fractal manner from a central point. They are poised to become the cornerstone of nanoscale devices in several fields, ranging from biomedicine to light-harvesting. Technical difficulties in obtaining these molecules has slowed their transfer from academia to industry. In 2001, the arrival of the "click chemistry" concept gave the field a major boost. The flagship reaction, a modified Hüisgen cycloaddition, allowed researchers greater freedom in designing and building dendrimers. In the last five years, advances in click chemistry saw a wider use of other click reactions and a notable increase in the complexity of the reported structures. This review covers key developments in the click chemistry field applied to dendrimer synthesis from 2010 to 2015. Even though this is an expert review, basic notions and references have been included to help newcomers to the field.

The influence of pentafluorophenyl groups on the nonlinear optical (NLO) performance of high generation dendrons and dendrimers

With the aim to make the influence of pentafluorophenyl groups in the periphery of high generation dendrons and dendrimers on their NLO performance clearly, some NLO dendrons and dendrimers with different chromophore moieties or different end-capped groups were carefully designed and investigated in detail. The results demonstrated that some strong Ar-Ar^F interactions between the pentafluorophenyl groups in the periphery and the normal phenyl rings of the donors, could influence the topological structures of dendrons or dendrimers, and then affect their NLO performance. Furthermore, the optical transparency and the stability of the dendrons and dendrimers with pentafluorophenyl groups as end-capped moieties were all improved, in comparison with normal dendrons and dendrimers containing phenyl ones as the end-capped groups.

Novel electro-optic chromophores based on substituted benzo[1,2-b:4,5-b′]dithiophene π-conjugated bridges

The electro-optic coefficient of benzo[1,2-b:4,5-b′]dithiophene unit (BDT)-based chromophores was improved to 102 pm V⁻¹ with suitable isolation groups and electron donors.

Comparison of nonlinear optical chromophores containing different conjugated electron-bridges: the relationship between molecular structure-properties and macroscopic electro-optic activities of materials

In electro-optic (EO) materials, realization of large EO coefficients for organic EO materials requires the simultaneous optimization of chromophore first hyperpolarizability, acentric order, molecular shape etc.

Dendrimers with large nonlinear optical performance by introducing isolation chromophore, utilizing the Ar/ArF self-assembly effect, and modifying the topological structure

By the combination of divergent and convergent approach, a new series of NLO dendrimers (G1-PFPh-NS-GL to G3-PFPh-NS-GL) was conveniently prepared with satisfied yields through the powerful "click chemistry" reaction, in which perfluoroaromatic rings were introduced in the periphery, two types of chromophores were arranged with regular AB structure, and their topological structure was improved to a more spherical shape. All the dendrimers demonstrated good processability, and G1-PFPh-NS-GL exhibited the highest NLO effect of 221 pm/V among the three dendrimers.