Gupta Mayank, Zhu Ziyu, Kottilil Dileep, Rath Bibhuti Bhusan, Tian Wang, Tan Zhi-Kuang, Liu Xiaogang, Xu Qing-Hua, Ji Wei, Vittal Jagadese J
Department of Chemistry, National University of Singapore, Singapore 117543, Singapore.
Department of Physics, National University of Singapore, Singapore 117542, Singapore.
ACS Appl Mater Interfaces. 2021 Dec 22;13(50):60163-60172. doi: 10.1021/acsami.1c17327. Epub 2021 Dec 7.
A change in the degree of interpenetration (DOI) in metal-organic frameworks (MOFs) prompted by heat, pressure, or exchange of solvents is a fascinating phenomenon that can potentially impact the functional properties of MOFs. Structural transformation involving two noncentrosymmetric MOFs with different DOIs provides a rare opportunity to manipulate their optical properties. Herein, we report an unusual single-crystal-to-single-crystal (SCSC) transformation of a noncentrosymmetric 7-fold interpenetrated diamondoid () Cd(II) MOF into another noncentrosymmetric but 8-fold interpenetrated MOF upon the removal of guest solvents. A hydrogen-bond network formed between the lattice solvents and linker -2-(4-pyridyl)-4-vinylbenzoate (pvb) in a 7-fold interpenetrated noncentrosymmetric MOF results in a significant increase in the two-photon absorption cross-section (11 times) as compared to that in the desolvated 8-fold interpenetrated MOF. Also, an increase in the DOI in the noncentrosymmetric crystals strengthened the π···π interaction between the individual diamondoid networks and enhanced the second-order nonlinear optical (NLO) coefficient (deff) by 4.5 times. These results provide a way to manipulate the optical properties of MOFs using a combined strategy of the formation of hydrogen bonds and interpenetration for access to tunable single-crystal NLO devices in an SCSC manner. By changing the experimental conditions, another Cd(II) MOF with 4-fold interpenetration can be isolated. In this centrosymmetric MOF, the olefin groups in the backbone of the ligand (pvb) undergo a [2 + 2] cycloaddition reaction quantitatively under UV light but in a non-SCSC fashion.
由热、压力或溶剂交换引发的金属有机框架（MOF）中互穿程度（DOI）的变化是一种引人入胜的现象，可能会对MOF的功能特性产生潜在影响。涉及两种具有不同DOI的非中心对称MOF的结构转变为操纵其光学性质提供了难得的机会。在此，我们报道了一种非中心对称的7重互穿类金刚石（）Cd（II）MOF在去除客体溶剂后发生不寻常的单晶到单晶（SCSC）转变，形成另一种非中心对称但8重互穿的MOF。在7重互穿的非中心对称MOF中，晶格溶剂与连接体-2-（4-吡啶基）-4-乙烯基苯甲酸酯（pvb）之间形成的氢键网络导致双光子吸收截面相比去溶剂化的8重互穿MOF显著增加（11倍）。此外，非中心对称晶体中DOI的增加增强了各个类金刚石网络之间的π···π相互作用，并使二阶非线性光学（NLO）系数（deff）提高了4.5倍。这些结果提供了一种通过形成氢键和互穿的组合策略来操纵MOF光学性质的方法，以便以SCSC方式获得可调谐的单晶NLO器件。通过改变实验条件，可以分离出另一种具有4重互穿的Cd（II）MOF。在这种中心对称的MOF中，配体（pvb）主链中的烯烃基团在紫外光下定量地发生[2 + 2]环加成反应，但不是以SCSC方式。
