Fluorescent copolymer aggregate sensor for lithium chloride

We report a copolymeric fluorescent sensor that is selective for lithium chloride. The two constituent polymers comprise pendent triphenylethylene (TPE) moieties for aggregate induced emission (AIE) along with either strapped-calix[4]pyrrole or secondary ammonium groups that drive aggregation via self-assembly upon polymer mixing. Addition of LiCl in acetonitrile disrupts the strapped-calix[4]pyrrole/secondary ammonium chloride salt host–guest crosslinks leading to disaggregation of the polymer chains and a decrease in TPE emission. The lack of AIE perturbation upon addition of NaCl, KCl, MgCl2 or CaCl2 provides for high selectivity for LiCl relative to potential interferants. This supramolecular dual polymer approach could serve as a complement to more traditional sensor systems.


Materials and methods
All reagents and starting materials were obtained from commercial suppliers and used without further purification unless otherwise noted. Compounds 1 S1 and monomer 7 S2 were prepared according to published procedures. One-dimensional nuclear magnetic resonance (NMR) spectra were recorded on Agilent MR 400 and Varian Inova 500 instruments. ESI mass spectra were obtained on an Agilent Technologies 6530 Accurate-Mass Q-TOF LC/MS or a Thermo Scientific TSQ Quantum GC/MS. An attenuated total reflection cell equipped with a Ge crystal was employed.
Fluorescence measurements were performed on a Perkin-Elmer Luminescence Spectrophotometer LS 50B or a Gilden Photonics Ltd. fluorimeter. Transmission electron microscopy (TEM) studies were carried out on a HITACHI HT-7700 instrument. Gel permeation chromatography (GPC) was performed on a Tosoh EcoSEC HLC-8320 GPC System equipped with a series of TSKgel SuperHM-H, -M, and -N columns. The instrument is equipped with a refractive index (RI) and ultraviolet (UV) absorbance detector (UV-8320). The instrument was run with HPLC-grade tetrahydrofuran as the eluent with toluene as an internal standard, at a flowrate of 0.35 mL/min, temperature of 40 °C, and injection volume of 50-100 μL. Prior to injection, all samples were dissolved fully in the mobile phase at a concentration of ~1-5 mg/mL and passed through a 0.45 μm syringe filter. Molecular weight and molecular weight distributions for the samples were estimated using a calibration curve generated from a set of poly(methyl methacrylate) standards (PstQuick® Kit-H) purchased from Tosoh Bioscience. S3

Synthesis of guest monomer 5
Fig. S1. Synthetic route to guest monomer 5.

Determination of the association constant for H⊃G
To determine the stoichiometry and association constant corresponding to the presumed interaction between H (Host) and G (Guest), 1 H NMR spectroscopic titrations were carried out using solutions that had a constant concentration of Host (5.00 mM) and varying concentrations of Guest. Using a non-linear curve-fitting method, the association constant corresponding to the interaction between guest Guest and Host was calculated. While not a proof, a 1:1 stoichiometry was inferred on the basis of a mole ratio (Job) plot.
The non-linear curve-fitting was based on the following equation: [S4]
Azobisisobutyronitrile (AIBN; 1.60 mg, 0.010 mmol) was added in one portion. The mixture was stirred for 10 min, sealed with a rubber septum and heated to 70 o C for 24 h. Polymerization was quenched by rapid freezing in liquid nitrogen. The solution was dropped into 500 mL of methanol, and the precipitated solid was collected by vacuum filtration. The precipitate was dissolved in THF and then dropped into methanol to obtain the precipitate again, which was repeated three times.
The collected polymer was dried in vacuum; yield 705 mg (61%).  Table S1. GPC analysis of polymer P1 using conventional calculations, with polystyrene as the standard and DMF as the solvent.
According to Mn and the ratio of x1/y1/z1, the values of x1, y1, and z1 were calculated to be 153, 12.3 and 9.4, respectively.

S25
Polymer P2 was prepared from compounds 5, 8, and methyl acrylate by free radical polymerization. The solution was dropped into 500 mL of methanol, and the precipitated solid was collected by vacuum filtration. The precipitate was dissolved in THF and then dropped into methanol to obtain the precipitate again, which was repeated three times. The collected polymer was dried in vacuum; yield 600 mg (52%).     Crystals grew as clusters of colorless prisms by slow evaporation from acetonitrile. The data crystal was separated from a cluster of crystals and had approximate dimensions; 0.24 x 0.13 x 0.032 mm.

The instrument parameter conditions of the fluorescence test
The data were collected on an Agilent Technologies SuperNova Dual Source diffractometer using a -focus Cu K radiation source ( = 1.5418 Å) with collimating mirror monochromators. A total of 1042 frames of data were collected using -scans with a scan range of 1 and a counting time of 13.5 seconds per frame for frames collected with a detector offset of +/-41.6 and 40.5 seconds per frame with frames collected with a detector offset of 107.1. The data were collected at 100 K using an Oxford Cryostream low temperature device. Details of crystal data, data collection and structure refinement are listed in Table S3. Data collection, unit cell refinement and data reduction were performed using Rigaku Oxford Diffraction's CrysAlisPro V 1.171.41.93a. S3 The structure was solved by direct methods using SHELXT S4 and refined by full-matrix least-squares on F 2 with anisotropic displacement parameters for the non-H atoms using SHELXL-2018/3. S5 Structure analysis was aided by use of the programs PLATON S6 and OLEX2. S7 The hydrogen atoms on the carbon atoms were calculated in ideal positions with isotropic displacement parameters set to 1.2xUeq of the attached atom (1.5xUeq for methyl hydrogen atoms).
The crystal was twinned. The twin law was determined using the CrysAlisPro software. The methyl ester group attached to the phenyl ring of the calixpyrrole cryptand was disordered about two positions. Refining the site occupancy factors resulted in a 77/23 mix of the two groups. Two fully occupied molecules of acetonitrile were also disordered. The function, w(|F o | 2 -|F c | 2 ) 2 , was minimized, where w = 1/[((F o )) 2 + (0.1123*P) 2 ] and P = (|F o | 2 + 2|F c | 2 )/3. R w (F 2 ) refined to 0.192, with R(F) equal to 0.0589 and a goodness of fit, S, = 1.06. Definitions used for calculating R(F), R w (F 2 ) and the goodness of fit, S, are given below. S8 The data were checked for secondary extinction effects but no correction was necessary. Neutral atom scattering factors and values used to calculate the linear absorption coefficient are from the International Tables for X-ray S33 Crystallography (1992). S9 All Figures were generated using SHELXTL/PC. S10 Tables of positional   and

Computational methods
The structures were optimized with quantum mechanics / density functional theory (DFT) in the Orca program S11 (version 4.1.0) at the B3LYP/Def2-SVP level with Grimme's third generation dispersion correction with Becke Johnson damping S12 (D3BJ