Electro-optic Chromophore Research Articles

Enhanced Photorefractive Performance by Controlling Ion‐Assisted Charge Injection and Accumulation with Random Biphenyl Co‐Polymerized Poly(Carbazolyl‐Amine)

AbstractIn this study, the synthesis of poly(carbazolyl‐amine)s with a random co‐polymerized biphenyl group through the Buchwald–Hartwig amination to enhance ion‐assisted space‐charge‐limited current (SCLC) and achieve efficient performance in photorefractive (PR) polymers, is reported. By modulating the polymer crystallinity, the efficient accumulation of ions near an electrode is achieved and enhanced ion‐assisted SCLC is realized, which results in a magnified electric field inside the polymers. The internal electric field is increased by the stacked charges injected from the electrode, and it is further enhanced by the washing out of ions. The polymer, blended with the electro–optical chromophore and sensitizer, exhibits a high PR sensitivity of 16.7 cm3 kJ−1 and a device stability of up to E = 80 V µm−1 at a wavelength of 633 nm, which is comparable to that of the inorganic crystals Bi12SiO20 and Sn2P2S6.

Organic Electro-Optic Materials with High Electro-Optic Coefficients and Strong Stability.

The preparation of high-performance electro-optical materials is one of the key factors determining the application of optoelectronic communication technology such as 5G communication, radar detection, terahertz, and electro-optic modulators. Organic electro-optic materials have the advantage of a high electro-optic coefficient (~1000 pm/V) and could allow the utilization of photonic devices for the chip-scale integration of electronics and photonics, as compared to inorganic electro-optic materials. However, the application of organic nonlinear optical materials to commercial electro-optic modulators and other fields is also facing technical bottlenecks. Obtaining an organic electro-optic chromophore with a large electro-optic coefficient (r33 value), thermal stability, and long-term stability is still a difficulty in the industry. This brief review summarizes recent great progress and the strategies to obtain high-performance OEO materials with a high electro-optic coefficient and/or strong long-term stability. The configuration of D-π-A structure, the types of materials, and the effects of molecular engineering on the electro-optical coefficient and glass transition temperature of chromophores were summarized in detail. The difficulties and future development trends in the practical application of organic electro-optic materials was also discussed.

Evaluation of Optical Characteristics in Electro‐Optic Chromophores Designed for Applications at O‐Band

Herein, lots of electro‐optic (EO) chromophores designed for applications at O‐band are synthesized, and the first hyperpolarizability β of EO chromophores is evaluated by the hyper‐Rayleigh scattering (HRS) technique. EO chromophores are constituted of various tricyanofuran (TCF) derivatives as the electron acceptor unit, thienyl‐di‐vinylene or thienyl‐di‐vinylene with ethylenedioxy as the π‐conjugation unit, and aminobenzene with a benzyloxy group as the donor unit. Halogen phenyl group or trifluoromethyl‐phenyl group in TCF acceptor unit leads to a relatively large improvement in β values. Furthermore, EO polymers with some promising EO chromophores that are suitable for the applications at O‐band (1260–1360 nm) are synthesized, and EO coefficient r33 (or n3r33) and absorption loss α are evaluated. Considering the trade‐off relationship between r33 (or n3r33) and α, EO polymers with excellent EO chromophores in the C‐band (1530–1565 nm) are not necessarily suitable EO polymers in the O‐band (1260–1360 nm). EO polymers with the O‐band chromophores have small α and moderate r33 (or n3r33) at the O‐band, while EO polymers with the C‐band chromophores have large α and slightly modified r33 (or n3r33) at the O‐band. The development of suitable EO chromophores and polymers for O‐band and C‐band respectively is very important.

Electro-optic crosslinkable chromophores with ultrahigh electro-optic coefficients and long-term stability.

The development of organic electro-optic materials with ultrahigh electro-optic coefficients and high long-term alignment stability is the most challenging topic in this field. Next-generation crosslinkable nonlinear optical chromophore molecular glasses were developed to address this problem. A highly stable EO system including crosslinkable binary chromophores QLD1 and QLD2 or crosslinkable single chromophore QLD3 and multichromophore QLD4 with large hyperpolarizability was synthesized using tetrahydroquinoline as the donor. When the temperature continues to rise after poling, the chromophores modified with anthracene and acrylate can undergo Diels-Alder crosslinking reaction to fix the oriented chromophores through chemical bonds. After crosslinking, the QLD1/QLD2 and QLD2/QLD4 films achieved very high maximum r 33 values of 327 and 373 pm V-1, respectively, which are the highest values reported for crosslinkable chromophore systems. After Diels-Alder cycloaddition, the glass transition temperature of the EO film increased by ∼90 °C to 185 °C, which is higher than for any other pure chromophore films. After being annealed at 85 °C, 99.63% of the initial r 33 value could be maintained for over 500 h. The ultrahigh electro-optic activity and high long-term alignment stability of these materials showed new breakthroughs in organic EO materials for practical device explorations.

Hypothetically Inspired Electro-Optic Chromophores for Laser Space Communication Applications

This paper describes the theoretically engineered electro optic chromophore (bromine based) and various characteristics of the chromophore. The simulation of halogen based (chlorine and bromine) electro optic chromophore is done. This chromophore can be especially used in the prospective applications due to its exceptional properties and conclusion drawn from the theoretically engineered electro optic chromophore. The halogens because of their electronic configuration tend to attain the stability with the other compound due to inductive effect. The halogen based chromophore enables the stable charge transfer due to change in the internal energy level The factors responsible for the enhancement of hyperpolarizability of the simulated chromophores which can lead to further advancement in the laser space communications applications are discussed.

Design and synthesis of chromophores with enhanced electro-optic activities in both bulk and plasmonic-organic hybrid devices.

This study demonstrates enhancement of in-device electro-optic activity via a series of theory-inspired organic electro-optic (OEO) chromophores based on strong (diarylamino)phenyl electron donating moieties. These chromophores are tuned to minimize trade-offs between molecular hyperpolarizability and optical loss. Hyper-Rayleigh scattering (HRS) measurements demonstrate that these chromophores, herein described as BAH, show >2-fold improvement in β versus standard chromophores such as JRD1, and approach that of the recent BTP and BAY chromophore families. Electric field poled bulk devices of neat and binary BAH chromophores exhibited significantly enhanced EO coefficients (r33) and poling efficiencies (r33/Ep) compared with state-of-the-art chromophores such as JRD1. The neat BAH13 devices with charge blocking layers produced very large poling efficiencies of 11.6 ± 0.7 nm2 V-2 and maximum r33 value of 1100 ± 100 pm V-1 at 1310 nm on hafnium dioxide (HfO2). These results were comparable to that of our recently reported BAY1 but with much lower loss (extinction coefficient, k), and greatly exceeding that of other previously reported OEO compounds. 3 : 1 BAH-FD : BAH13 blends showed a poling efficiency of 6.7 ± 0.3 nm2 V-2 and an even greater reduction in k. 1 : 1 BAH-BB : BAH13 showed a higher poling efficiency of 8.4 ± 0.3 nm2 V-2, which is approximately a 2.5-fold enhancement in poling efficiency vs. JRD1. Neat BAH13 was evaluated in plasmonic-organic hybrid (POH) Mach-Zehnder modulators with a phase shifter length of 10 μm and slot widths of 80 and 105 nm. In-device BAH13 achieved a maximum r33 of 208 pm V-1 at 1550 nm, which is ∼1.7 times higher than JRD1 under equivalent conditions.

Electro-optical properties of doped polymers with high transparency in the visible wavelength range

The electro-optical (EO) properties of poly(methyl methacrylate) and the photopolymer poly(vinyl cinnamate) doped with varying concentrations of the EO chromophore 2-Methyl-4-nitroaniline were measured. The EO polymers were embedded in Fabry-Pérot etalons for the simultaneous determination of the Pockels and Kerr coefficients from measurements of the fringe shift induced by an external electric field. It was found that the host polymer has a significant impact on the EO performance and that the undoped host polymers exhibit a significant Pockels effect. Moreover, the Kerr effect provides a substantial contribution of 27% to the total change of the refractive index at relatively high electric field strengths of E = 91.2 MV m−1.

Electro-Optic Modulation Using Metal-Free Perovskites.

Electro-optic (EO) modulation is of interest to impart information onto an optical carrier. Inorganic crystals-most notably LiNbO3 and BaTiO3-exhibit EO modulation and good stability, but are difficult to integrate with silicon photonic technology. Solution-processed organic EO materials are readily integrated but suffer from thermal degradation at the temperatures required in operating conditions for accelerated reliability studies. Hybrid organic-inorganic metal halide perovskites have the potential to overcome these limitations; however, these have so far relied on heavy metals such as lead and cadmium. Here, we report linear EO modulation using metal-free perovskites, which maintain the crystalline features of the inorganic EO materials and incorporate the flexible functionality of organic EO chromophores. We find that, by introducing a deficiency of cations, we reduce the symmetry in the perovskite crystal and produce thereby an increased EO response. The best-engineered perovskites reported herein showcase an EO coefficient of 14 pm V-1 at a modulation frequency of 80 kHz, an order of magnitude higher than in the nondefective materials. We observe split peaks in the X-ray diffraction and neutron diffraction patterns of the defective sample, indicating that the crystalline structure has been distorted and the symmetry reduced. Density functional theory (DFT) studies link this decreased symmetry to NH4+ deficiencies. This demonstration of EO from metal-free perovskites highlights their potential in next-generation optical information transmission.

Substituent engineering of electrooptic chromophores to suppress their aggregation

Chromophores composed of 4-cyano-5-dicyanomethylene-2-oxo-3-pyrroline (CDCOP) and a donor have been synthsized for electrooptic applications. Three substituents of [5-(4-aminophenyl)-2-thienyl]-substituted CDCOP 1 and (4-aminophenyl)-substituted CDCOP 2 were modified to suppress the aggregation for effective poling. To 1, bulky and branched 2-ethylhexyl groups were introduced instead of linear alkyl groups. Less aggregation was confirmed in the polymer dispersion films, and the corona poling behaviors were examined. To 2, we introduced norbornyl epoxide groups as bulky and thermally crosslinkable moieties. The aggregation was suppressed as well, and the thermal crosslinking of the epoxide with acid anhydride in the presence of a base was investigated.

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 ( Tg = 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.

Adamantyl and carbazole containing trans-poly(norbornene-dicarboximide)s as electro-optic chromophore hosts

A selection of trans-poly(norbornene-dicarboximide) random copolymers incorporating adamantyl and carbazole groups have been prepared using the Grubbs 1st generation catalyst. The copolymer with the greatest carbazole content was employed as a host for a high activity chromophore guest. The adamantyl groups were able to elevate the glass transition and thermal decomposition temperatures of the host copolymers, while the carbazole groups were included to facilitate the dispersion of the added chromophores and enhance the poling process. The mass of the adamantyl pendant monomer was kept constant as the mass of the carbazole pendant monomer was increased gradually. The successful incorporation of the carbazole moiety into the copolymers was confirmed by 1H NMR integration. The polymers had a predominantly trans microstructure and the cis/trans ratio did not change significantly. The polymer molecular weights increased linearly from 25,758 g/mol to 56,827 g/mol as more carbazole-pendant monomer was incorporated. Polydispersities ranged from 1.29 to 1.70 and elemental analysis confirmed an ascending carbon% in the polymers from 72.29% to 76.26%. The glass transition temperatures decreased from 240 °C to 126 °C, with the thermal decomposition temperatures (10% loss) remaining relatively constant at between 423 °C to 394 °C, indicating the polymers had a good thermal stability. The chromophore guest concentration was increased gradually into the copolymer host from 15 wt% to 65 wt%. When poled at a field of 50 V/μm in thin film it was found that the optimum poling temperature decreased linearly from 150 °C to 90 °C as the chromophore concentration was increased, a maximum poling efficiency of 1.02 was achieved at a chromophore concentration of 55 wt%.

A photo-functional electro-optic polyimide with excellent high-temperature stability

We herein report the preparation of a soluble polyimide from a photoreactive diamine and a phenolic diamine, to which electro-optic (EO) properties were imparted by the introduction of an EO chromophore (Disperse Red 1) into the phenolic group of the polyimide. Following poling at 1 MV/cm and 210 °C, the polyimide was irradiated with UV light (280–310 nm) to form a photo-crosslinking network. The EO coefficient of the polyimide-containing EO device was 27.7 p.m./V at 1.3 μm, and this value was maintained at ≥90%, even after annealing at 150 °C for 500 h. Our results indicated that the thermal and chemical stabilities of the EO polyamide were remarkably increased due to the photo-crosslinking reaction.

A Method for Measuring the Electro-optical Response of Chromofore-embedded Polymer Films Using a Prism Coupler

When electro-optical chromophores are embedded into a polymer matrix and aligned in a preferential direction, it becomes possible to control the refraction of light in such a composite medium under the influence of an external electric field. This effect is used in the production of high-speed integrated-optical modulators, switches, etc. We manufactured nonlinear optical polymethyl methacrylate (PMMA) films into which the DR13 chromophore was embedded. An algorithm is created that allows one to determine the electro-optical parameters of films in a multilayer anisotropic structure with metal electrodes, when a control voltage is supplied to them. The electro-optical coefficients r33 and r13 of the PMMA/DR13 composite were found at several wavelengths near the DR13 chromophore absorption peak and far from it. The proposed method makes it possible to measure the electric-field-induced change in the refractive index in the thin-film light-guiding structure of an actual electro-optical modulator with an accuracy of ±0.0005.

Crosslinked poly(norbornene-dicarboximide)s as electro-optic chromophore hosts

A series of crosslinked poly(norbornene-dicarboximide)s have been prepared by ring opening metathesis polymerization. Increasing quantities of a bifunctional norbornene-dicarboximide crosslinker was doped into a high Tg cyclohexyl-substituted norbornene-dicarboximide monomer before polymerization. The wt% of the crosslinker was increased from 0.00 to 4.40wt%, after which the polymers became gelated. Polymer molecular weights increased drastically from 23,500 to 2,135,000 g/mol, the polydispersities increased from 1.18 to 73.47 and the viscosities increased from 5.27 to 538.7 mPa·s as the wt% of the crosslinker was increased. The trans:cis vinylene ratio remained constant at 1:0.18 as well as the Tg and Td with average values of 210 °C and 392 °C being measured. Five of the crosslinked polymers and the reference homopolymer were utilized as hosts for the high activity tert-butyldiphenylsilyl substituted FTC chromophore guest. The polymer host containing 1.96wt% crosslinker was found to have a maximum r33 of 78 pm/V when polled at 150 °C with an electric field strength of 100 V/μm. The r33 increased linearly from 63 to 78 pm/V as the wt% of the crosslinker was increased from 0.00 to 1.96wt%. The thermal and temporal stability was found to increase slightly with the 0.00wt% polymer exhibiting a stability of 77%, while the 1.96wt% polymer exhibited a stability of 79% when both were heated to 85 °C and aged for 500 h in air.

Novel poly(aryl ether ketone) with electro-optic chromophore side chains for light modulators

Organic nonlinear optical materials have been widely explored because of their advantages in the design of materials with large electro-optic coefficients used in the fabrication of novel optoelectronic and telecommunication devices. However, the huge dipole–dipole interactions between organic nonlinear optical chromophores have limited further improvements in the electro-optic coefficients and long-term material stability. Here, a novel polymer based on poly(aryl ether ketone) was designed and prepared to enhance the electro-optic coefficients and achieve higher long-term stability. This novel poly(aryl ether ketone) has a relatively high glass transition temperature and offers active functional groups for the attachment of organic nonlinear optical chromophores. After attachment of nonlinear optical chromophores the materials showed higher chromophore loading density, less inter-molecular interaction, and suitable solubility. This resulted in better film-forming ability, higher electro-optics coefficients and better long-term stability. Quantum chemical simulations of the second order hyperpolarizabilities and ground sate dipole moments were done to understand the origin of the effects.

Bandwidth improvement of microwave photonic components based on electro-optic polymers loaded with TiO2 nanoparticles

Electro-optic (EO) polymers offer a very attractive possibility of realizing low-cost microwave photonic components with a wide bandwidth and a low driving voltage, thanks to a low dispersion from microwave to optical frequency of polymeric materials on the one hand, and the progress in the synthesis of high hyperpolarizability chromophores on the other hand. This paper studies the influence of titanium dioxide (TiO2) nanoparticle loading on the microwave and optical properties of EO polymers. Thus, poly(methyl methacrylate) (PMMA) and disperse red 1 (DR1) are used as host polymer and guest EO chromophore, respectively. With 1–3% TiO2 nanoparticle homogeneously incorporated in the polymer, the dielectric constant varies from 2.73 to 3.40 over the 400 MHz–10 GHz range, and the refractive index increases from 1.483 to 1.488 at the wavelength of 1539.6 nm. It is shown that fine tuning of dielectric constant and refractive index could allow improvement of the microwave photonic component bandwidth. For example, with an EO interaction length L = 2 cm (typical length of EO modulators), the ultimate modulator bandwidth could be raised to 258 GHz by loading PMMA–DR1 EO polymer with 1% wt of TiO2 nanoparticles. It is also found that loading polymer with nanoparticles could improve the EO response of poled polymers, represented by the intensity of the second-harmonic-generation (SHG) signal. The latter presents more than a threefold increase by loading PMMA–DR1 EO polymer with 2% wt TiO2 nanoparticles.

Effect of Rigid Bridge-Protection Units, Quadrupolar Interactions, and Blending in Organic Electro-Optic Chromophores

A new organic electro-optic (EO) molecule was designed with two modifications aimed at increasing acentric order. The molecule is based on the well-known CLD donor-π bridge-acceptor template. The first structural modification introduces rigid aromatic fluorenyl and naphthyl site-isolation units (sterically bulky functional groups) to reduce aggregation. Site isolation units have been used in the past, but this is the first time that both the “front” and “back” of the CLD tetraene bridge have been modified with site-isolation units, and we had to introduce new synthetic methodology to do so. The second design element was the inclusion of cooperatively interacting aromatic dendron (HD) and fluoroaromatic dendron (FD) side groups to increase the acentric order. HD/FD units have previously been successfully used to increase EO performance, but we changed their location on the chromophore: they are attached to the donor and acceptor ends of the molecule to better match side chain ordering with the dipole momen...

Formation of channel optical waveguides in polymethylmethacrylate with embedded electro-optic chromophore DR13 by the photoinduced bleaching method

A composite polymeric material based on polymethylmethacrylate (PMMA) with embedded electro- optical (EO) chromophore DR13 is designed. Irradiation with electromagnetic radiation in the visible range leads to a bleaching of the composite and its refractive index n decreases due to the irreversible photodestruction of the chromophore. Changes in the absorption spectrum and refractive index of the composite with the irradiation time are measured. It is shown that the change in n depends on the concentration of DR13 in the polymer matrix and can reach a value of Δn = 0.034 in the telecommunication C-range near a wavelength of 1.55 μm. The rate of bleaching depends on the wavelength of the actinic light and reaches its maximum when the wavelength is near the maximum of chromophore absorption. With the use of the photobleaching method and the PMMA/DR13 composite, channel waveguides and the other elements of the integrated optical devices are fabricated, including waveguide splitters, directional couplers, and Mach–Zehnder interferometers. This simple one-step method does not involve the removal of polymer material by liquidphase or reactive ion etching.

Synthesis and Characterization of Novel Second-Order Nonlinear Optical Chromophore with Multi-Hydroxyl Groups Donor

ABSTRACTNew electro optical chromophore with 4-(bis(2-hydroxyethyl)amino)-2,6-dipropoxybenzaldehyde as electron donor was synthesized and characterized by 1H NMR spectra and mass spectra. Four hydroxyl groups were introduced to the electron donor, which could be easily reacting with carboxyl, isocyanate, anhydride, and so on, to afford us second-order nonlinear optical polymers. Chromophore T showed us good solubility in common solvents, thermal stability (above 200°C) and expected Uv-vis absorption. In this article, polymethyl methacrylate (PMMA) doped with chromophore T at different loading density was prepared to second- order nonlinear optical films by spin coating. These films showed us large second-order nonlinear optical coefficients, 13.5, 19.7, 24.3, and 26.4 pm/V for the second-order nonlinear optical films with chromophore loading density of 10 wt%, 20 wt%, 30 wt%, and 40 wt%, respectively.

Important role of the ethylenedioxy group bound to the thienyl-di-vinylene π-conjugation unit of tricyanofuran-based donor-acceptor electro-optic chromophores

We report the design, synthesis and characterization of a series of electro-optic chromophores comprised of amino-benzene with a benzyloxy group as the donor units, thienyl-di-vinylene with ethylenedioxy as the π-conjugation bridge, and tricyanofuran derivatives as the acceptor units. The improvement of linear and nonlinear optical properties was found in electro-optic chromophores with ethylenedioxy compared with the chromophores without ethylenedioxy. The data obtained from hyper-Rayleigh scattering, absorption spectrum, and 1H-NMR measurements indicate the improved structural stability of π-conjugation unit, which may be induced by the steric effect and partial intra-molecular hydrogen bonding related to ethylenedioxy.