Choi Kyu-Ri, Kim Dae Hyeon, Lee Yeon Ui, Placide Virginie, Huynh Steven, Yao Dandan, Canard Gabriel, Zaborova Elena, Mathevet Fabrice, Mager Loïc, Heinrich Benoît, Ribierre Jean-Charles, Wu Jeong Weon, Fages Frédéric, D'Aléo Anthony
Department of Physics, Ewha Womans University Seoul 03760 Republic of Korea
Department of Physics, Chungbuk National University Chungbuk 28644 Republic of Korea.
RSC Adv. 2021 Nov 29;11(60):38247-38257. doi: 10.1039/d1ra08025c. eCollection 2021 Nov 23.
Epsilon-near-zero (ENZ) properties have been reported in organic molecular films. In particular, cyanine and squaraine films have been shown to exhibit ENZ properties in the visible spectral region with a strong 3 order nonlinear optical response near the ENZ spectral region. Noting both cyanine and squaraine belong to the polymethine family, a series of six curcuminoid borondifluoride (Curc) derivatives were developed to examine whether such a polymethine character is positively correlated with the ENZ property of the organic films. Those Curc derivatives possess a Donor-Acceptor-Donor (D-A-D) architecture with acceptor, AcacBF, located at the molecular center. The backbone of Curc is designed such that the donor strength can be tuned to transit between charge transfer (CT) and polymethine character. This balance between CT and polymethine character of the Curc series is examined based on the Lippert-Mataga plot. As donor strength in the D-A-D structure increases, CT character is less marked resulting in a more dominant polymethine character. The structural and optical properties of the Curc films with a thickness in the order of 30 nm were examined to correlate the polymethine character with the ENZ response. The results obtained in isotropic Curc thin films demonstrate that an increase of polymethine character associated with a stronger donor strength leads to an appearance/enhancement of the ENZ property in the visible spectrum range from 500 to 670 nm. Overall, this study provides useful guidelines to engineer new organic materials showing ENZ properties in a desired spectral range.
在有机分子薄膜中已报道了近零介电常数（ENZ）特性。特别是，菁和方酸菁薄膜已被证明在可见光谱区域表现出ENZ特性，并且在ENZ光谱区域附近具有强烈的三阶非线性光学响应。鉴于菁和方酸菁都属于聚甲炔家族，因此开发了一系列六种姜黄素硼二氟化物（Curc）衍生物，以研究这种聚甲炔特性是否与有机薄膜的ENZ特性呈正相关。这些Curc衍生物具有供体-受体-供体（D-A-D）结构，受体AcacBF位于分子中心。Curc的主链设计成可以调节供体强度，以便在电荷转移（CT）和聚甲炔特性之间转换。基于Lippert-Mataga图研究了Curc系列在CT和聚甲炔特性之间的这种平衡。随着D-A-D结构中供体强度的增加，CT特性变得不那么明显，从而导致聚甲炔特性更加占主导地位。研究了厚度约为30nm的Curc薄膜的结构和光学性质，以关联聚甲炔特性与ENZ响应。在各向同性的Curc薄膜中获得的结果表明，与更强的供体强度相关的聚甲炔特性的增加会导致在500至670nm可见光谱范围内ENZ特性的出现/增强。总体而言，本研究为设计在所需光谱范围内显示ENZ特性的新型有机材料提供了有用的指导。
