posted on 2021-12-07, 18:34authored byMayank Gupta, Ziyu Zhu, Dileep Kottilil, Bibhuti Bhusan Rath, Wang Tian, Zhi-Kuang Tan, Xiaogang Liu, Qing-Hua Xu, Wei Ji, Jagadese J. Vittal
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 (dia) Cd(II) MOF into another noncentrosymmetric
but 8-fold interpenetrated dia MOF upon the removal of
guest solvents. A hydrogen-bond network formed between the lattice
solvents and linker trans-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 dia 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.