Selective detection of DABCO using a supramolecular interconversion as fluorescence reporter

The quantitative double self-sorting between the three-component rectangle [Cu4(1)2(2)2]4+ and the four-component sandwich complex [Cu2(1)(2)(4)]2+ is triggered by inclusion and release of DABCO (4). The fully reversible and clean switching between two multicomponent supramolecular architectures can be monitored by fluorescence changes at the zinc porphyrin sites. The structural changes are accompanied by a huge spatial contraction/expansion of the zinc porphyrin–zinc porphyrin distances that change from 31.2/38.8 Å to 6.6 Å and back. The supramolecular interconversion was used for the highly selective detection of DABCO in a mixture of other similar compounds.


General remarks on instrumentation and chemicals
All solvents were dried by distillation prior to use while commercial reactants (4, 9, 10) were utilized without any further purification. A Bruker Avance (400 MHz) spectrometer was employed to measure 1 H and 13 C NMR spectra using a deuterated solvent as the lock and residual protiated solvent as internal reference (CDCl3: δH 7.26 ppm, δC 77.0 ppm; CD2Cl2: δH 5.32 ppm, δC 53.8 ppm, THF-d8: δH 1.72 ppm, 3.58 ppm, δC 25.3 ppm, 67.2 ppm). The following abbreviations were used to define NMR peak patterns: s = singlet, d = doublet, t = triplet, br = broad, m = multiplet. The coupling constants are given in hertz (Hz) and, wherever possible, assignment of protons is made. The carbons in the molecular skeletons are mostly not numbered following the IUPAC nomenclature rules; it was exclusively done for assigning NMR signals. All electrospray ionization (ESIMS) spectra were recorded on a Thermo-Quest LCQ deca and the theoretical isotopic distributions of the mass signals were calculated using the IsoPro 3.0 software. Melting points of compounds were measured on a Büchi 510 instrument and are not corrected. Infrared spectra were recorded on a Varian 1000 FTIR instrument. Elemental analysis was performed using the EA-3000 CHNS analyzer. UV-vis spectra were recorded on a Cary Win 50 (298 K) spectrometer. Binding constants were determined through S3 UV-vis titrations assuming a 1:1 binding scheme or with the SPECFIT/32 TM global analysis system by Spectrum Software Associates (Marlborough, MA). Column chromatography was performed either on silica gel (60-400 mesh) or neutral alumina (Fluka, 0.05-0.15 mm, Brockmann Activity 1).

General remarks on synthetic schemes
Chart S1: Ligands used in the present study.
Scheme S1. Synthetic scheme used in the preparation of ligands 1 and 2.

Synthesis of porphyrin 3 4
Under a nitrogen atmosphere, Rh2(CO)4Cl2 (47.0 mg, 121 µmol) and 5,10,15,20-tetraphenylporphyrin (50.0 mg, 81.3 µmol) were dissolved in anhydrous CH2Cl2 (10 mL). After the addition of anhydrous NaOAc (198 mg, 2.42 mmol) stirring was continued for 45 min. Avoiding any exposure to air, the reaction mixture was concentrated under vacuum (5 min, to remove residual acetic acid), a new portion of CH2Cl2 (10 mL) was added, and the procedure was repeated. The reaction mixture was dissolved in dry benzene (10 mL) and I2 (21.0 mg, 121 µmol) was added. The progress of oxidation was monitored by UV-vis analysis and TLC. As soon as the reaction was completed (45 min), the mixture was transferred to a silica column and the product was eluted with CH2Cl2.

Synthesis and characterization of model complexes
General procedure: All solid compounds were placed in an NMR tube and then dissolved in CD2Cl2.

Measurement of binding constants
The UV-vis titration technique was used to determine the binding constants of complexes. The full data of a selected wavelength region was analyzed using the SPECFIT/32 global analysis system (Spectrum Software Associates, Marlborough, MA).