Photoswitching of halide-binding affinity and selectivity in dithienylethene-strapped calix[4]pyrrole

Dithienylethene-strapped calix[4]pyrrole is isomerized by 300/630 nm light between ring-open and -closed isomers, which affects the size of the anion binding site. Where for chloride this results in only a small change in affinity, that of the larger bromide and iodide ions is majorly affected, resulting in altered selectivity.


Experimental section General methods and materials:
THF, MeCN, and Et2O were dried using a Pure Solve 400 solvent purification system from Innovative Technology. Dry DMF was acquired from Acros Organics and DMSO-d6, MeCN-d3, acetone-d6 and methanol-d4 were purchased from Eurisotop. DMSO-d6 was stored under N2 over molecular sieves (4Å). Degassing of solvents was carried out by purging with N2 for 30 min, unless noted otherwise. Compounds (o)-2 1 and 5 2 were prepared using procedures reported in the literature. All other chemicals were commercial products and were used without further purification. Column chromatography was performed using silica gel (SiO2) purchased from Screening Devices BV (Pore diameter 55-70 Å, surface area 500 m 2 g -1 ).
Thin-layer chromatography (TLC) was carried out on aluminum sheets coated with silica 60 F254 and neutral aluminum oxide obtained from Merck. Compounds were visualized with UV light (254 nm). Melting points were determined using a Büchi M560 apparatus. 1 H, 13 C and 19 F NMR spectra were recorded on Bruker AV 400 and Bruker 500 Ultra Shield instruments at 298 K unless indicated otherwise. Chemical shifts () are denoted in parts per million (ppm) relative to residual protiated solvent (DMSO-d6: for 1 H detection,  = 2.50 ppm; for 13 C detection,  = 39.52 ppm; MeCN-d3: for 1 H detection,  = 1.94 ppm; for 13 C detection,  = 1.32 and 118.26 ppm; acetone-d6 for 1 H detection,  = 2.05 ppm; for 13 C detection,  = 29.84 and 206.26 ppm; methanol-d3 for 1 H detection,  = 3.31 ppm; for 13 C detection,  = 49.0 ppm. The splitting pattern of peaks is designated as follows: s (singlet), d (doublet), dd (double doublet), t (triplet), m (multiplet), and br (broad). IR spectra were recorded on a Perkin Elmer Spectrum Two FT-IR spectrometer. The wavenumber () is in units of reciprocal centimeters (cm −1 ) and the intensity is designated as follows: s (strong), m (medium), w (weak), very w (very weak), br (broad), and sh (shoulder). High-resolution mass spectrometry (ESI-MS) was performed on a Thermo Scientific Q Exactive HF spectrometer with ESI ionization. UV-Vis spectra were recorded on an Agilent Cary 8454 spectrometer using 1 cm or 1 mm quartz cuvettes. ITC measurements were performed using a MicroCal VP-ITC MicroCalorimeter. Irradiation of UV-Vis and NMR samples was carried out using Thorlab model M300F2 (4.8 mW) and 630E (7.2 mW) LEDs positioned at a distance of 1 cm.

Single crystals of (o)-1 obtained by slow evaporation of a solution in CH2Cl2/EtOH:
All reflection intensities were measured at 110(2) K using a SuperNova diffractometer

Single crystals of (c)-1 obtained by cooling of a solution in MeCN (to -7 °C):
All reflection intensities were measured at 110(2) K using a SuperNova diffractometer  Disorder and lattice solvent molecules are omitted for clarity. Table S3. Crystallographic data for the structure of (c)-1.

H NMR titration experiments
First, a solution of (o)-1 (~2 mM in MeCN-d3) was prepared, which was then used to prepare a more concentrated solution of the tetrabutylammonium anion. The solution containing the anion was added stepwise to the solution of (o)-1 and after each addition a 1 H NMR spectrum was recorded. For the titrations to (c)-1, the solution of (o)-1 was irradiated at 300 nm until the PSS ratio was (nearly) reached, before using it to prepare the anion solution. The titration experiment was performed in the dark to avoid back-isomerization from (c)-1 to (o)-1.
Titration of NBu4Cl to (o)-1: Figure S15. 1    The binding constant ratio was determined by integration of the pyrrole-NH (Ha, Ha') signals using the first three 1 H NMR spectra. The ratio was calculated using the following equation:

ITC titration experiments
The titrations were carried out by adding 6 L aliquots of a solution of (o)-1 in degassed MeCN to an approximately 17 times more concentrated solution of tetrabutylammonium chloride or tetrabutylammonium bromide in the same solvent at 298 K. To calculate the association constants and thermodynamic parameters, the data (measured in duplo) was fitted to a "one set of sites" binding model using the Origin software in the ITC module. S33