Understanding the Linear and Second-Order Nonlinear Optical Properties of UiO-66-Derived Metal–Organic Frameworks: A Comprehensive DFT Study

Abstract

Periodic density functional theory calculations have been performed to investigate the structures, the linear and second order nonlinear optical (NLO) properties of Zr-based UiO-66 metal−organic frameworks, in which the 1,4-benzene-dicarboxylate (BDC) linkers are functionalized by a series of isovalent substituents including −NH 2 , −OH, −SH, and halogen atoms. Our results show that the mixed phase will be formed for the case of the incorporation of a single hydroxyl or halogen atom, while it is more likely to synthesize the pure phase for the homodifunctionalized compounds. The ligand functionalization results in the appearance of the band gap states as well as the narrowing of the band gap. For the linear optical response, besides the redshift of the absorption edge, the ligand modification tends to increase the dielectric constant and enhance the optical anisotropy of UiO-66, especially when two −SH groups are incorporated into the BDC ligand. With regard to the NLO activity, the second harmonic generation (SHG) intensity of the pristine UiO-66 is comparable to that of KDP. The SHG response of UiO-66 can be effectively improved by the single-site substitution, and the obvious enhancement of the SHG activity is observed after introducing the sulfydryl group or the iodine atom. However, it is noted that the difunctionalizations by two −OH and −SH have a relatively weak impact on the SHG intensity because of the nearly centrosymmetric organization of the homodifunctionalized organic linkers. Among all derivatives, UiO-66-(SH) 2 is the most promising candidate for use as a near-infrared NLO material with a strong SHG effect (>20 pm/V) and good phase matchability. Furthermore, the primary origin of the SHG response for UiO-66 and its derivatives is determined by analyzing the band structure. This study reveals the possibility of designing NLO materials with outstanding performances based on the UiO-66-derived MOFs through rational functionalization of the organic linking unit.

Salicylideneaniline-Based Covalent Organic Frameworks: A New Family of Multistate Second-Order Nonlinear Optical Switches

“…In this way, contrary to other methods that have been employed to calculate the optical responses of molecular crystals and MOFs, this method does not suffer from various limitations: (i) in the cluster approach, the optical responses depend on the cluster size and shape as well as on the way the dangling bonds are saturated, 45 (ii) it does not involve a two-step procedure where molecular responses need to be computed first before evaluating the macroscopic ones, 46,47 and (iii) with respect to other PBCbased perturbative approaches, it does not require the use of a scissor operator to correct the underestimated band gaps. 48,49 The number of nonequivalent nonzero χ (1) and components depends on the space group (in particular, in centrosymmetric crystals, all χ (2) tensor components vanish). These components are listed in Table S1.…”

“…This approach presents some advantages to calculate the χ (1) and χ (2) responses because it provides these responses in a single step. In this way, contrary to other methods that have been employed to calculate the optical responses of molecular crystals and MOFs, this method does not suffer from various limitations: (i) in the cluster approach, the optical responses depend on the cluster size and shape as well as on the way the dangling bonds are saturated, (ii) it does not involve a two-step procedure where molecular responses need to be computed first before evaluating the macroscopic ones, , and (iii) with respect to other PBC-based perturbative approaches, it does not require the use of a scissor operator to correct the underestimated band gaps. , …”

A Theoretical Perspective on Strategies for Modeling High Performance Nonlinear Optical Materials

“…According to a recent research on ZIF-8 (zeolitic imidazolate) framework (Van Cleuvenbergen et al, 2016), it is observed that ZIF-8 has a strong SHG signal that is similar to the inorganic crystals of KH 2 PO 4 . A theoretical investigation on the structures and exploration of NLO response of experimentally synthesized Zr-based UiO-66 MOFs with BDC (1,4-benzene-dicarboxylate) linkers and its substituents (−NH 2 , −OH, −SH, and halogen atoms) has been carried out to reveal the effect of ligand functionalization on NLO properties (Ni et al, 2020). Recently, the NLO response of titanium-based MIL-125 MOFs (crystals) has been investigated using DFT calculations.…”

Significant second-harmonic generation and bulk photovoltaic effect in trigonal selenium and tellurium chains

“…Second-harmonic generation(SHG), the bestknown nonlinear optical (NLO) responses, have promising applications in probes of surfaces and interfaces, frequency doublers, and so on. Notably, it has been investigated extensively in bulk semiconductors [2][3][4][5][6][7][8][9] for nearly five decades beginning in the early 1960s. More recently, the family of NLO materials has also been extended to one-dimensional (see, e.g., refs 10-11 and references therein) and two-dimensional (see, e.g., refs 12-17 and references therein) systems, crucial for the development modern optical and electro-optical devices such as frequency conversions, electro-optic modulators, and switches.…”