Guest‐Triggered Aggregation‐Induced Emission in Silver Chalcogenolate Cluster Metal–Organic Frameworks

Abstract Utilizing aggregation‐induced emission luminogens (AIEgens) as ligands has proven to be an effective strategy for constructing metal–organic frameworks (MOFs) with intense luminescent properties. However, highly luminescent AIEgen‐based MOFs with adjustable emission properties are rarely achieved because of the rigid conformation of AIEgens in the crystalline state. Here, a dual‐node 3D silver chalcogenolate cluster MOF (1) is designed and synthesized, where the AIE ligand shows relatively flexible and rotatable conformations. The conformations of AIE ligands in 1 are switchable by the absorption/desorption of guest molecules. As a result, 1 exhibited not only intense but also guest molecule switched luminescent properties. More importantly, the switching rate is tunable by using different guest molecules. 1 provides a unique visualized prototype to understand the mechanism of guest‐triggered aggregation‐induced emission in MOFs.


Reagents
Unless otherwise noted, all materials used in this work were commercially available and used as received. 1,1,2,2-tetrakis(4-bromophenyl)ethene was purchased from AIEgen Biotech Co., Limited.

Apparatus
PXRD data were carried out at room temperature in air using PANalytical-X P PRO (Mo-K ). Thermogravimetry analysis (TGA) of the compounds was conducted on a SHIMADZU TGA-Q50 thermogravimetric analyzer from room temperature to 400 o C at a heating rate of 10 o C/min under N 2 atmosphere. Nuclear magnetic resonance (NMR) data were collected on a Bruker 400 Avance NMR spectrometer operated at 400 MHz at room temperature. The elemental analysis was performed by Thermo Flash EA 1112 Analyzer. Fluorescence spectra, lifetimes and quantum yields were obtained on Edinburgh FLS-980 fluorescence spectrometer. For fluorescence lifetime measurements, a 370 nm-laser was used, which was operated in time-correlated single photon counting mode (TCSPC) with a resolution time of 100 ns. For fluorescence quantum yields measurements, an integrating sphere was used. Infrared spectra were obtained on PerkinElmer Spectrum Two FT-IR Spectrometer. Ultraviolet-visible diffuse reflectance spectra (UV-DRS) were performed in JASCO-750 UV-vis spectrophotometer, BaSO 4 was used as reference. The photos and videos were taken by OLYMPUS BX53 microscope and NIKON D5500 camera.

TGA analysis
As shown in Figure S6A, the original molecular weight of 1 (1 with no DMAC) was 4207, while 71% quality remained at 400 o C, which suggested the final molecular weight of 1 was 4207×71%=2987.

Single crystal X-ray diffraction measurements
Single crystal X-ray diffraction measurement of 1 DMAC sealed in a capillary tube with mother liquor was carried out on a Rigaku XtaLAB Pro diffractometer with Mo-K radiation (= 0.71073 Å) at 100 K. Data collection and reduction were performed with CrysAlisPro. [2] Multi-scan absorption corrections were applied to the data using CrysAlisPro. [2] The structure were solved with intrinsic phasing methods (SHELXT-2015), and refined by full-matrix least squares on F 2 using OLEX2 using the SHELXL-2015 module. [3,4] All non-hydrogen atoms, including the disordered fragments were located in difference-Fourier maps, O atoms, C atoms and N atoms of DMAC molecule were refined isotropically and all other non-hydrogen atoms in the framework were refined anisotropically. All hydrogen atoms were assigned isotropic displacement coefficients U(H) = 1.2 U or 1.5 U and their coordinates were allowed to ride on their respective atoms. Silver atom Ag 3 and Ag 5 are disordered in the set ratio of 0.80:0.20, the set ratios of Ag 4 , Ag 2 , Ag 8 are 0.87:0.13, 0.85:0.15 and 0.7:0.3, respectively. The t-butyl moiety and trifluoroacetate anions were also found to be disordered. Therefore, the PART instruction was used to divides them into two groups. The leastsquares refinement of the structural model was performed under hard geometry restraints and displacement parameter restrains, such as SADI, SIMU, ISOR, DELU, DANG, DFIX and FLAT for the CF 3 CO 2 -, S t Bu and DMAc molecule. The main solvent peaks were located and refined with the partial occupancies which due to the seriously disorder arising from the thermal motion or dynamic locating of the DMAC in the large solvent accessible space. The remaining unassigned electron densities were removed using SQUEEZE program implemented in PLATON. One Alert B, the missing of FCF reflections below theta (Min), was found in the checkcif file because the low-angle reflections were attenuated by the beam stop. The other three alerts B were ascribed to disordered molecules in the structure, and the short contact between disordered fragments is to be expected. The imposed restraints and constraints in least-squares refinement of the structure were commented in the CIF file. The crystal structure was visualized by Diamond 3.2. [5] Crystal data are summarized in Table S2.
The CIF file can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif (CCDC 1857863 for 1 DMAC).

Calculation of void space
The void space was calculated from its X-ray structural data by PLATON. [6] The calculation method is as follows: The unit cell contains the atoms from the structural model. Every specific atom is assigned its van der Waals radius, respectively. A list of grid points with a minimum distance of 1.2 Å (from the nearest van der Waals surface) was generated from grid search. Then this list of grid points is applied to produce a new list of grid points, making up the solvent accessible areas. Then the center of T are used to calculate the overall solvent accessible volume.

Density functional theory (DFT) calculation procedure
The DFT calculation were performed with Gaussian 09 [7] under M062X functional. [8] The calculations were conducted using 6-31g** basis set for C and N atoms. [9] The single crystal structure of 1 DMAC was chosen as initial guess for ground state optimization. Figure S1. The structure and coordination mode of Ag 8 cluster.