Switching-On Fluorescence by Copper (II) and Basic Anions: A Case Study with a Pyrene-Functionalized Squaramide †

The new symmetric acyclic N,N’-bis(1-pyrenyl) squaramide (H2L) functionalized with the pyrene moiety as a fluorogenic fragment has been designed and its ability to selectively detect specific anions and metals investigated. H2L selectively binds Cl− both in solution (DMSO 0.5% H2O and MeCN) and in the solid state, and allows to selectively detect Cu2+ in MeCN with the formation of a 2:1 metal-receptor complex, with a green intense emission appreciable by naked eye under the UV lamp. The H2L copper complex preserves its emission properties in the presence of Cl−. The addition of basic anions (OH−, CN−, and F−) up to 10 equivalents caused the deprotonation of the squaramide NHs and a dramatic change of the emission properties of the H2L copper complex.


D H A d(D-H)/Å d(H-A)/Å d(D-A)/Å D-H-A/deg
168.0 ----1 -x,1-y,-z; 2 1-x,-y,-z. The structure solved and the space group P21/n (# 14) determined by the ShelXD (Sheldrick, 2008) structure solution program using Dual Space and refined by Least Squares using version 2018/3 of ShelXL . All non-hydrogen atoms were refined anisotropically. The positions of the N-H atoms H1, H2, H3, and H4 were located from the electron difference map and refined with their thermal parameters linked to their parent atoms. The positions of the remaining C-H atoms were calculated geometrically and refined using the riding model.

_refine_special_details:
The crystal is a merohedral twin; an appropriate twin law has been applied to the refinement. The disordered DMSO solvent molecules have been modelled over two or three positions, using thermal and geometric parameter restraints ( Figure S14). The value of Z is 4 and Z' is 2. There are two independent molecules and four solvent DMSOs in the asymmetric unit ( Figure S15). Figure S14. The disordered DMSO solvent molecules within A, thermal ellipsoids drawn at the 50% probability level, minor component(s) were drawn with ghosted colours. 13.3% Figure S15: The asymmetric unit of A, thermal ellipsoids drawn at the 50% probability level, disorder shown. X-ray data collected upon a yellow (cut) lath-shaped crystal (0.198×0.047×0.030 mm 3 ), mounted on a MITIGEN holder with perfluoroether oil; using a Rigaku FRE+ diffractometer, equipped with Varimax confocal mirrors, an AFC12 goniometer, a HyPix 6000 detector and an Oxford Cryosystems low-temperature device, operating at T = 100(2) K.

2) Structure (B): H2L • Cl
Data measured using profile data from -scans of 0.5 ° per frame for 19.0 s using Mo K radiation (Rotating Anode, 45.0 kV, 55.0 mA). The total number of runs and images based on the strategy calculation from the program CrysAlisPro (Rigaku, V1.171.41.89a, 2020 The structure was solved in the space group P-1 (# 2) by using dual methods using ShelXT 2018/2  and refined by full matrix least squares minimisation on F 2 using ShelXL 2018/3 . All non-hydrogen atoms were refined anisotropically. The positions of N-H atoms H1 and H2 were located from the electron difference map and refined with their thermal parameters linked to their parent atoms; with the positions of the solvent water O-H and all the remaining C-H atoms, calculated geometrically and refined using the riding model.
_refine_special_details: This sample contained both block-like and plate-like yellow crystals; this data is from a representative block-like crystal. The disordered atoms of the TBA ions (C39a/C39b, C40a/C40b, C43a/C43b, C44a/C44b, C54a/C54b > C56a/C56b, and C58a/C58b > C60a/C60b) are modelled over two positions using thermal and geometric parameter restraints and the disordered waters/chloride ion sites, are modelled using thermal parameter restraints. The occupancy ratio between these water/chloride ion sites is freely refined very close to 1:1; therefore, for all subsequent refinements this ratio was fixed at 0.5:0.5. In addition, all of the water molecules were modelled and refined as rigid bodies with idealised geometries. Applying the above to the refinement, conserved realistic chemical geometries and lowered R1 from 7.67% to 5.82%.
Z is 2 and Z' is 1. There is a single ligand molecule, four chloride ions, four TBA ions and seven solvent water molecules in the asymmetric unit, represented by the reported sum formula.