Fluorinated Organic Electro‐Optic Quinolinium Crystals for THz Wave Generation

Kim, Se‐In; Kang, Bong Joo; Jeong, Chan-Uk; Shin, Myeong‐Hoon; Kim, Dong-Won; Jazbinšek, Mojca; Yoon, Woojin; Yun, Hoseop; Kim, Dong-Wook; Rotermund, Fabıan; Kwon, O‐Pil

doi:10.1002/adom.201801495

Cited by 13 publications

(16 citation statements)

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“…[12][13][14] Various quinolinium electron acceptors instead of pyridinium electron acceptors were introduced into nonlinear optical chromophores to increase their nonlinearity. [8,[22][23][24][25][26][27][28][29][30] The electron withdrawing strength of quinolinium electron acceptors is higher than that of the pyridinium group; e.g., compared to the widely used 1,4-dimethylpyridinium electron acceptor, introducing 1,2-dimethylquinolinium electron acceptor results in enhancing the molecular optical nonlinearity of chromophores by about 50% at 1550 nm in solution. [30] Among quinolinium-based crystals, to our knowledge only phenolic crystals exhibit state-of-the-art macroscopic optical nonlinearity; e.g., eff β iii > 150 × 10 −30 esu.…”

Section: Introductionmentioning

confidence: 99%

“…[30] Among quinolinium-based crystals, to our knowledge only phenolic crystals exhibit state-of-the-art macroscopic optical nonlinearity; e.g., eff β iii > 150 × 10 −30 esu. [24][25][26][27][28] Therefore, the macroscopic optical nonlinearities of phenolic quinolinium-based crystals are still near the level of pyridinium-based DAST crystals ( 111 eff β = 161 × 10 −30 esu).…”

Section: Introductionmentioning

confidence: 99%

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Organic THz Generators: A Design Strategy for Organic Crystals with Ultralarge Macroscopic Hyperpolarizability

Seok

Kim

et al. 2021

Advanced Optical Materials

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include the submillimeter wavelengths of terahertz (THz) frequencies. Examples of such applications are THz wave generation and detection, cross-phase modulation, and THz nonlinear optics. [1][2][3][4][5][6][7] Compared to inorganic crystals, the organic alternatives exhibit superior macroscopic second-order optical nonlinearity, which often shows one order of magnitude larger nonlinear optical and electro-optic coefficients. [8] There is still a strong demand for improving the macroscopic optical nonlinearity of organic crystals, which is presently below the level achieved in the organic poled polymers. For example, the electro-optic coefficient of benchmark organic crystals is at the level of ≈50 pm V −1 at 1.3 µm. [9][10][11] On the other hand, the poled polymer systems may exhibit much larger electro-optic coefficients, up to ≈500 pm V −1 at 1.3 µm. [12][13][14] However, progress on designing a strategy to exceed the limits of the state-of-the-art optical nonlinearity of current benchmark organic crystals seems to be slow. Moreover, besides the large macroscopic optical nonlinearity desired, many other crystal characteristics that make possible to grow high-quality bulk crystals with plate-like crystal morphology and high thermal stability are required for real-world photonic applications.Developing new organic crystals with large macroscopic second-order optical nonlinearity is a challenging issue Newly designed halogenated organic quinolinium crystals proposed in this work provide fully optimized molecular ordering for maximizing the optical nonlinearity and high-performance broadband terahertz (THz) wave generation. The ultralarge diagonal optical nonlinearity (almost 300 × 10 −30 esu) of the new halogenated crystals is approximately two times larger than that of state-of-the-art pyridinium-based crystals. In contrast, nonhalogenated analogous crystals exhibit very low (or vanishing) diagonal optical nonlinearity. This is attributed to halogen-induced unique interionic interactions and finetuning of the space-filling characteristics. In addition, the halogenated crystals show a good ability for bulk crystal growth of few millimeters lateral size with plate-like morphology and high thermal stability that are finally required for real-world applications. The new halogenated quinolinium crystals exhibit excellent THz wave generation characteristics, significantly surpassing the limit of conversion efficiency and spectral bandwidth of inorganic benchmark crystals. A 0.16 mm thick chlorinated crystal generates a 29-times larger THz field than 1.0 mm thick inorganic ZnTe crystals at 1500 nm pump wavelength with a flat and broadband spectrum extending up to ≈8 THz. Therefore, introducing halogen substituents is a potential design strategy for designing new organic crystals showing ultralarge macroscopic hyperpolarizability and high-performance THz wave generation.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Organic THz Generators: A Design Strategy for Organic Crystals with Ultralarge Macroscopic Hyperpolarizability

Seok

Kim

et al. 2021

Advanced Optical Materials

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“…in organic NLO crystals. [164,[191][192][193] In crystals, the introduction of halogen substituents (F, Cl, and Br) has multiple merits. The simultaneous electron-withdrawing and electrondonating effects of halogen substituents (Cl and Br) induce unique and strong multiple interionic interactions with both the existing partially positive σ-holes and the partially negative belts (e.g., Cl substituents in cationic chromophores and anions in Figure 18c [193] ).…”

Section: Phonon Mode Engineeringmentioning

confidence: 99%

“…The introduction of halogen substituents in cationic chromophores and/or anions results in the modulation and enhancement of THz wave generation characteristics. [164,[191][192][193] Adv. Optical Mater.…”

Section: Phonon Mode Engineeringmentioning

confidence: 99%

Highly Nonlinear Optical Organic Crystals for Efficient Terahertz Wave Generation, Detection, and Applications

Kim

Kang

Puc

et al. 2021

Advanced Optical Materials

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ordering in the crystalline state should be simultaneously considered when designing organic π-conjugated crystals to achieve the desired physical properties. However, the prediction of the molecular ordering of organic π-conjugated chromophores in the crystalline state is still significantly difficult. This is because most organic π-conjugated chromophores exhibit several complex intermolecular and intramolecular interactions (and interionic interactions) with multiple possible molecular conformations during the self-assembling process in the crystalline state. [17,18] For each specific target application, a different targeted control of the molecular ordering of chromophores in the crystalline state is required, which is still an important issue in the molecular (and crystal) engineering of various organic π-conjugated crystalline materials.This issue is more critical for organic nonlinear optical (NLO) crystals and will be the focus of this review. Organic NLO crystals can be used in diverse nonlinear photonic applications, such as frequency down-and up-conversion, terahertz (THz) wave generation and detection, phase and amplitude electro-optic modulation, and high-speed telecommunication integrated optics. [19][20][21][22][23] Organic crystals must possess a noncentrosymmetric molecular ordering of chromophores to achieve second-order optical nonlinearity. However, in addition to the aforementioned complicated molecular interactions, the introduction of strong polar substituents (electron-donating groups (EDGs) and electron-withdrawing groups (EWGs)) on widely used push-pull π-conjugated chromophores to increase their molecular nonlinearity also increases their dipole moment. In many cases, a high dipole moment leads to a centrosymmetric ordering of chromophores with antiparallel dipole-dipole aggregation in the crystalline state (i.e., there is no macroscopic second-order optical nonlinearity). This tendency further complicates the development of new organic NLO crystals with large second-order optical nonlinearity. This is one of the reasons for only a few classes of organic crystals with state-of-theart optical nonlinearity being reported in the last few decades. Moreover, in addition to large macroscopic second-order optical nonlinearity, different NLO applications require different targeted physical properties (e.g., refractive index, dispersion of the refractive index, dielectric constant, and absorption coefficient) and crystal characteristics (e.g., direction of the polar axis, morphology, aperture size, thickness, and facets). Therefore, it Organic π-conjugated crystals with second-order optical nonlinearity are considerably attractive materials for diverse terahertz (THz) wave photonics. An overview of the research of organic nonlinear optical (NLO) crystals for THz wave generation, detection, and applications is provided here. First, the status of organic NLO crystals compared to other alternative THz materials is described. Second, the basic theory and requirements for organic THz generators and d...

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“…Since most organic compounds are centric without nonlinear optical properties, it is essential to obey two simple rules in order to obtain organic NLO crystals, namely, (i) introducing a strong electron donor (D) and acceptor (A) system to obtain enhanced microscopic optical susceptibility and (ii) making the molecules crystallize in the noncentrosymmetric space group to ensure large macroscopic optical nonlinearity for efficient THz output. For a long time, the design strategy was focused on the selection and optimization of ionic type D−π–A systems, which lead to the development of several classical combinations of electron donor and acceptor, such as pyridinium-based cations (OHP, (C 14 H 14 NO) + ), quinolinium-based cations (HMQ, (C 19 H 18 NO 2 ) + ; − OHQ, (C 18 H 16 NO) + ), − benzothiazolium-based cations (HMB, (C 17 H 16 NO 2 S) + ); HDB, (C 18 H 18 NOS) + ), and indolium-based cations (OHI, (C 19 H 20 NO) + ) . These ionic type organic NLO crystals exhibit large second order harmonic generation (SHG) intensity, at least ∼ 0.7 times of commercial OH1 crystal ( d 33 = 120 pm/V at 1.9 μm), and have achieved effective THz generation in a wide frequency range of 0.1 ∼ 20 THz.…”

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confidence: 99%

Steric Group Design for Enhancement of Optical Nonlinearity in Isoxazolone-Based Crystals and Terahertz-Wave Generation

Gao

Zhang

et al. 2021

Crystal Growth & Design

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Isoxazolone-based crystals are one of the important molecular type nonlinear optical crystals, which can exhibit good output properties in the terahertz region. In this work, by rational steric group design, three novel isoxazolone-based nonlinear optical crystals of C16H11NO3 (OH-PYO, Fdd2), C13H13NO3 (OH-IPO, Fdd2), and C15H17NO3 (HD-IPO, Pca21) and were successfully synthesized and grown by evaporation method. The optimization of steric group from phenyl (−C6H6) to isopropyl [−CH(CH3)3] effectively modified the molecular arrangement style and enhanced the powder second harmonic generation intensities of OH-IPO and HD-IPO to 0.7 and 0.8 times that of benchmark OH1 (d 33 = 120 pm/V at 1.9 μm) and 2 times higher than unoptimized OH-PYO. Remarkably, OH-IPO exhibited large band gap of 2.38 eV and wide transparency range (522–2150 nm), and its terahertz-wave generation was demonstrated for the first time by difference frequency generation method, indicating OH-IPO is a potential terahertz nonlinear optical material.

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Fluorinated Organic Electro‐Optic Quinolinium Crystals for THz Wave Generation

Cited by 13 publications

References 50 publications

Organic THz Generators: A Design Strategy for Organic Crystals with Ultralarge Macroscopic Hyperpolarizability

Organic THz Generators: A Design Strategy for Organic Crystals with Ultralarge Macroscopic Hyperpolarizability

Highly Nonlinear Optical Organic Crystals for Efficient Terahertz Wave Generation, Detection, and Applications

Steric Group Design for Enhancement of Optical Nonlinearity in Isoxazolone-Based Crystals and Terahertz-Wave Generation

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