New design strategies for second-order nonlinear optical polymers and dendrimers

Suitable Isolation Side Chains: A Simple Strategy for Simultaneously Improving the Phototherapy Efficacy and Biodegradation Capacities of Conjugated Polymer Nanoparticles

Utilizing one molecule to realize combinational photodynamic and photothermal therapy upon single-wavelength laser excitation, which relies on a multifunctional phototherapy agent, is one of the most cutting-edge research directions in tumor therapy owing to the high efficacy achieved over a short course of treatment. Herein, a simple strategy of "suitable isolation side chains" is proposed to collectively improve the fluorescence intensity, reactive oxygen species production, photothermal conversion efficiency, and biodegradation capacity. Both in vitro and in vivo results reveal the practical value and huge potential of the designed biodegradable conjugated polymer PTD-C16 with suitable isolation side chains in fluorescence image-guided combinational photodynamic and photothermal therapy. These improvements are achieved through manipulation of aggregated states by only side chain modification without changing any conjugated structure, providing new insight into the design of biodegradable high-performance phototherapy agents.

Dendronized Hyperbranched Polymer: A New Architecture for Second-Order Nonlinear Optics

Organic/polymeric second-order nonlinear optical (NLO) materials, which rely on the poling-induced non-centrosymmetric arrangement of NLO chromophores, have played a very important role in laser technology and optical fiber communication, due to their ultra-fast response speed, excellent machining performance and low dielectric constant. However, the NLO chromophores have the large dipole moments with strong intramolecular charge transfer, which lead to the intermolecular electrostatic interactions to tend to the centrosymmetric arrangement and decrease the poling efficiency. Since the special three-dimensional spatial separation can minimize these strong intermolecular electrostatic interactions during poling process, dendrimers and hyperbranched polymers have been considered as better topology for the next generation of highly efficient NLO materials. In 2013, by the attachment of low generation dendrimers to the hyperbranched backbone, a new dendritic architecture of dendronized hyperbranched polymer (DHP) was proposed for improving the comprehensive performance of NLO materials. Recent results showed many advantages of DHPs in NLO field, such as easy syntheses, large NLO coefficients and high orientation stability, etc. In this review, the latest advancement of DHPs, including the design principle, synthesis, as well as their application as NLO materials is summarized. The new opportunities arising from DHPs are also summarized in the future perspective.

Modulating the optical properties and functions of organic molecules through polymerization

Organic functional materials with advanced optical properties have attracted much attention due to their broad applications, such as in light-emitting diodes, solar cells, anti-counterfeiting, photocatalysis, and even disease diagnosis and treatment. Recent research has revealed that many optical properties of organic molecules can be improved through simple polymerization. In this review, we discuss the phenomenon, mechanism, and impact of polymerization on the properties of materials, including the polymerization-induced spectral shift, polymerization-enhanced photosensitization, polymerization-enhanced two-photon absorption, polymerization-enhanced photocatalytic efficiency, polymerization-induced room temperature phosphorescence, polymerization-induced thermally activated delayed fluorescence, and polymerization-induced emission using specific examples with different applications. The new opportunities arising from polymerization in designing high performance optical materials are summarized in the future perspective.

Electro-Optic Activity in Excess of 1000 pm V-1 Achieved via Theory-Guided Organic Chromophore Design

High performance organic electro-optic (OEO) materials enable ultrahigh bandwidth, small footprint, and extremely low drive voltage in silicon-organic hybrid and plasmonic-organic hybrid photonic devices. However, practical OEO materials under device-relevant conditions are generally limited to performance of ≈300 pm V^-1 (10× the EO response of lithium niobate). By means of theory-guided design, a new series of OEO chromophores is demonstrated, based on strong bis(4-dialkylaminophenyl)phenylamino electron donating groups, capable of EO coefficients (r₃₃ ) in excess of 1000 pm V^-1 . Density functional theory modeling and hyper-Rayleigh scattering measurements are performed and confirm the large improvement in hyperpolarizability due to the stronger donor. The EO performance of the exemplar chromophore in the series, BAY1, is evaluated neat and at various concentrations in polymer host and shows a nearly linear increase in r₃₃ and poling efficiency (r₃₃ /E_p , E_p is poling field) with increasing chromophore concentration. 25 wt% BAY1/polymer composite shows a higher poling efficiency (3.9 ± 0.1 nm² V^-2 ) than state-of-the-art neat chromophores. Using a high-ε charge blocking layer with BAY1, a record-high r₃₃ (1100 ± 100 pm V^-1 ) and poling efficiency (17.8 ± 0.8 nm² V^-2 ) at 1310 nm are achieved. This is the first reported OEO material with electro-optic response larger than thin-film barium titanate.

Quadratic Non-Linear Optical Properties of the poly(2,5-bis(but-2-ynyloxy) Benzoate Containing the 2-(ethyl(4-((4-nitrophenyl)buta-1,3-diynyl)phenyl)amino)ethanol) Chromophore

Excellent quadratic non-linear optical (ONL-2) properties of the poly(2,5-bis(but-2-ynyloxy) benzoate, containing a polar diacetylene as a chromophore, were found. According with the Maker fringes method, oriented polymer films showing an order parameter of ∼0.23 can display outstanding and stable Second Harmonic Generation (SHG) effects under off-resonant conditions (SHG-532 nm). Also, the macroscopic non-linear optical (NLO)-coefficients were evaluated under the rod-like molecular approximation, obtaining: χ_zzz⁽²⁾ and χ_zxx⁽²⁾ in the order of 280 ± 10 and 100 ± 10 pm V^-1, respectively. The mechanical and chemical properties, in addition to the large ONL-2 coefficients exhibited by this polymer, make it a promising organic material in the development of optoelectronic/photonic devices.

Molecular Engineering of Structurally Diverse Dendrimers with Large Electro-Optic Activities

To boost electro-optic (EO) performance, a series of multichromophore dendrimers have been developed based on higher hyperpolarizability (CLD-type) chromophore cores that have been used previously (FTC-type dendrimers). The multichromophore dendrimers were molecularly engineered to have either three arms, two arms, or one arm; long or short linkers; and a fluorinated dendron (FD) or tert-butyldiphenylsilyl (TBDPS) shell. The EO performance obtained by FDSD (poling efficiency = 1.60 nm² V^-2), based on succinic diester linkers, was higher than the analogue with longer adipic diester linkers and higher than the analogs with fewer chromophore moieties. Due to the shorter succinic diester linker and improved site isolation, the dendrimer chromophore with TBDPS groups exhibited enhanced glass-transition temperature ( T_g = 108 °C) and comparable poling efficiency (1.62 nm² V^-2) to the FD-containing version. These neat EO dendrimers have a higher index of refraction ( n = 1.75-1.84 at 1310 nm) than guest-host polymeric EO materials ( n ≈ 1.6, 1310 nm) and FTC-type EO dendrimers ( n = 1.73, 1310 nm), which is important, because a key metric for Mach-Zehnder modulators is proportional to n³. In addition, binary chromophore organic glasses (BCOGs) were prepared by doping a secondary EO chromophore at 25 wt % into neat dendrimers. Enhancements of EO performance were found in all BCOG materials compared with neat dendrimers due to the effect of blending. As a result of increased chromophore density, the n values of the BCOGs improved to 1.81-1.92. One BOCG, in particular, displayed the highest poling efficiency (2.35 nm² V^-2) and largest EO coefficient ( r₃₃) value of 275 pm V^-1 at 1310 nm, which represents a high n³ r₃₃ figure-of-merit of 1946 pm V^-1. The high poling efficiencies and n³ r₃₃ figure-of-merit combined with excellent film forming confirm these neat dendrimers and BCOGs based on them as promising candidates for incorporation into photonic devices.

Transition metal-free thiol–yne click polymerization toward Z-stereoregular poly(vinylene sulfide)s

An efficient K₃PO₄-mediated thiol–yne click polymerization was established, and regio- and stereoregular poly(vinylene sulfide)s with Z-isomers were produced.

Photo-crosslinkable second-order nonlinear optical polymer: facile synthesis and enhanced NLO thermostability

A new photo-crosslinkable second-order nonlinear optical system was designed and prepared by azido-yne and the thiol–ene click reactions.

Unusual response to environmental polarity in a nonlinear-optical benzylidene-type chromophore containing a 1,3-bis(dicyanomethylidene)indane acceptor fragment

One of the strongest known electron-accepting fragments used in the synthesis of organic dyes for applications in nonlinear optics (NLO) is 1,3-bis(dicyanomethylidene)indane (BDMI). By studying a benzylidene-type push-pull chromophore bearing a 5-carboxy-BDMI electron-acceptor and 4-(dimethylamino)aniline donor fragment, we demonstrate that this class of compounds can show unusual response to the polarity of the surrounding medium. The combined results of UV-Vis absorption spectrometry, NMR experiments and computational modeling indicate that the studied compound undergoes a geometrical transformation that involves an increase in the torsion angle ω between the aniline and indane ring systems with the rise of the polarity of the surrounding medium. This process is partly facilitated by an increased rotational freedom around ω in more polar solvents, as detected experimentally by NMR and predicted by calculations. Regarding the practical application aspects, computations predict that the solvent-polarity-induced increase of torsion ω would lead to a notable decrease in the first hyperpolarizability (β) value. This was detected experimentally, as hyper-Rayleigh scattering (HRS) data showed a drop in the compound's NLO activity from β_HRS(532)  = 513 × 10^-30 esu in toluene to β_HRS(532)  =  249 × 10^-30 esu in acetonitrile. This places limitations on the NLO applications of the studied compound and its structural analogues, as the surrounding medium (solvent of polymer matrix) with the lowest possible polarity needs to be used to maximize their NLO efficiency.

A novel selenoalkenyl-isoxazole based donor-acceptor nonlinear optical material

The structure property relationships of untwinned enantiomorphic Z-(methylseleno)alkenyl-substituted phenyl-isoxazole and its isostructural triazole congener both crystallizing in the P2₁2₁2₁ space group were investigated with respect to UV/vis absorption, thermal behaviour, and second harmonic generation ability. Differential scanning calorimetry revealed a significantly higher melting point of the novel isoxazole compound compared to the triazole derivative and therefore a broader thermal application window. The SHG efficiency of the isoxazole derivative is approximately two thirds the value of the triazole compound and approximately 27 times higher than potassium dihydrogen phosphate. Thus, the developed molecular scaffold represents an interesting novel type of nonlinear optical (NLO) chromophore.

Perspective and Potential of Smart Optical Materials

The increasing requirements of hyperspectral imaging optics, electro/photo-chromic materials, negative refractive index metamaterial optics, and miniaturized optical components from micro-scale to quantum-scale optics have all contributed to new features and advancements in optics technology. Development of multifunctional capable optics has pushed the boundaries of optics into new fields that require new disciplines and materials to maximize the potential benefits. The purpose of this study is to understand and show the fundamental materials and fabrication technology for field-controlled spectrally active optics (referred to as smart optics) that are essential for future industrial, scientific, military, and space applications, such as membrane optics, light detection and ranging (LIDAR) filters, windows for sensors and probes, telescopes, spectroscopes, cameras, light valves, light switches, and flat-panel displays. The proposed smart optics are based on the Stark and Zeeman effects in materials tailored with quantum dot arrays and thin films made from readily polarizable materials via ferroelectricity or ferromagnetism. Bound excitonic states of organic crystals are also capable of optical adaptability, tunability, and reconfigurability. To show the benefits of smart optics, this paper reviews spectral characteristics of smart optical materials and device technology. Experiments testing the quantum-confined Stark effect, arising from rare earth element doping effects in semiconductors, and applied electric field effects on spectral and refractive index are discussed. Other bulk and dopant materials were also discovered to have the same aspect of shifts in spectrum and refractive index. Other efforts focus on materials for creating field-controlled spectrally smart active optics (FCSAO) on a selected spectral range. Surface plasmon polariton transmission of light through apertures is also discussed, along with potential applications. New breakthroughs in micro scale multiple zone plate optics as a micro convex lens are reviewed, along with the newly discovered pseudo-focal point not predicted with conventional optics modeling. Micron-sized solid state beam scanner chips for laser waveguides are reviewed as well.

Preparation of Main-Chain Polymers Based on Novel Monomers with D-π-A Structure for Application in Organic Second-Order Nonlinear Optical Materials with Good Long-Term Stability

Main-chain nonlinear optical polymers based on novel chromophores with special structures presented good solubility in most of the organic solvents. Polymers PE-1 and PE-2 attained the thermal decomposition temperatures of 305 and 223 °C and glass transition temperatures of 113 and 108 °C, and exhibited only negligible decay in the SHG signal baked at 85 °C over hundreds of hours, respectively. The SHG coefficients of poled films from polymers PE-1 and PE-2 were 26.3 and 35.8 pm/V, respectively. These results indicated that this class of polymers can be used in the preparation of organic electro-optic devices.

Structural control of side-chain chromophores to achieve highly efficient electro-optic activity

Chromophore J2 in APC provided the best balance between steric hindrance and molecular free mobility with excellent electro-optic coefficients.

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.

A series of dendronized hyperbranched polymers with dendritic chromophore moieties in the periphery: convenient synthesis and large nonlinear optical effects

Excellent optical transparency and NLO coefficients were achieved by introducing dendritic chromophore moieties to the periphery of dendronized hyperbranched polymers.

Design and preparation of hybrid films containing three-branched chromophores for nonlinear optical applications

A new hybrid film with homogeneous morphology is fabricated and exhibits excellent second nonlinear optical properties.

Synthesis and characterization of two novel second-order nonlinear optical chromophores based on julolidine donors with excellent electro-optic activity

Second order NLO chromophores with julolidine donor.

The synthesis of new double-donor chromophores with excellent electro-optic activity by introducing modified bridges

New double-donor chromophores were synthesized and large hyperpolarizability can be effectively translated into large electro-optic coefficients.

Dendronized hyperbranched polymers containing isolation chromophores: design, synthesis and further enhancement of the comprehensive NLO performance

New dendronized hyperbranched polymers (DHPs) constructed by dendronized monomers, exhibit good comprehensive NLO performance, especially for thermostability.

Main chain dendronized hyperbranched polymers: convenient synthesis and good second-order nonlinear optical performance

By using low generation dendrimers as macromonomers, two main chain dendronized hyperbranched polymers, with good comprehensive nonlinear optical performance, were prepared conveniently with satisfying yields through a one-pot “A₃ + B₂” approach.

Functional hyperbranched polymers with advanced optical, electrical and magnetic properties

This review summarizes the recent progress in functional HBPs and their application in optics, electronics and magnetics, including light-emitting devices, aggregation-induced emission materials, nonlinear optical materials, chemosensors, solar cells, magnetic materials, etc., and provides outlooks for further exploration in the field.

Synthesis and characterization of a novel second-order nonlinear optical chromophore based on a new julolidine donor

A new chromophore was synthesized and the hyperpolarizability can be effectively translated into large electro-optic coefficients in poled polymers.

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.