Enhanced Coplanarity and Giant Birefringence in Hydroxypyridinium Nitrate via Hydrogen Bonding between Planar Donors and Planar Acceptors

• Published in: Angewandte Chemie International Edition Vol. 64; no. 5; pp. e202417579 - n/a
• Main Authors: Yin, Jian‐Ping, Guo, Jingyu, Huo, Hao, Liu, Xin, Cheng, Xue‐Jie, Lin, Zheshuai, Wu, Li‐Ming, Chen, Ling
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 27.01.2025
• Edition: International ed. in English
• Subjects: Anisotropy; Birefringence; Calcium carbonate; Coplanar arrangement; Coplanarity; Crystals; Hydrogen; Hydrogen bond; Hydrogen bonding; Hydrogen bonds; Nitrates; Optical components; Second harmonic generation; Signal generation; Signal processing; Second harmonic generation; Birefringence; Coplanar arrangement; Hydrogen bond
• ISSN: 1433-7851; 1521-3773; 1521-3773
• DOI: 10.1002/anie.202417579

Birefringent crystals, which possess optical anisotropy, are important optical components. However, designing and synthesizing birefringent crystals faces the challenge of achieving anisotropic structures, especially coplanar geometries. Herein, we achieve a significant birefringence in an ionic compound (C5H6ON)+(NO3)−, (4‐hydroxypyridinium nitrate, 4HPN) by hydrogen bonding between planar donors and planar acceptors. We demonstrate that the interactions between the planar hydrogen bond donor ((C5H6ON)+) and planar hydrogen bond acceptor ((NO3)−) ensure the coplanarity during the crystal packing, generating the desired giant optical anisotropy. On two manually cut crystal chips, we observe a Δnobv. ${\Delta {n}^{obv.}}$ =0.494 ( Δnmaxcal. ${\Delta {n}_{max}^{cal.}}$ =0.593), which is the largest among nitrates, or hydroxypyridinium derivatives. This Δnobv. ${\Delta {n}^{obv.}}$ value already surpasses those of the benchmark crystals, e.g., YVO4 and CaCO3, commonly used in the UV to visible and near IR spectral range. 4HPN also exhibits a strong second harmonic generation response (9.55×KDP). This strategy offers a promising avenue for the design and development of birefringent crystals with potential applications in optical communication, sensing and signal processing devices. A strategy that utilizes hydrogen bonding between planar donors and planar acceptors is proposed. Guided by this stratedy, the giant birefringence achieved by ionic crystal, (C5H6ON)+(NO3)−, 4HPN, is achieved. This concept has convincingly demonstrated its applicability and relevance across a diverse array of systems, providing a guiding principle in design synthesis.