Intramolecular π-stacking interaction in a rigid molecular hinge substituted with 1-(pyrenylethynyl) units

Synthesis of a tetrakis(1-pyrenylethynyl)-substituted rigid hinge-like molecule (1) is described. The intramolecular π-stacking interaction of the pyrene units is studied by 1H NMR and fluorescence spectroscopy. Due to intramolecular π-stacking interactions, chemical shifts of the pyrene protons in 1 are highly shielded in the NMR spectrum. Fluorescence from the static excimer state is observed due to π-stacking interactions among the pyrene units in the ground state of 1. Based on the spectroscopic evidence, conformations and dynamics of 1, arising from the hindered rotation of the major axis, are proposed

Ligand dynamics in tetracoordinate copper(I) complexes of bis(pyrazolyl)pyridine ligands †

Several mononuclear and a binuclear copper(I)–phosphine complex with a tridentate ligand, L [2,6-bis(3,5-dimethylpyrazol-1-ylmethyl)pyridine] or L′ [2,6-bis(pyrazol-1-ylmethyl)pyridine], have been prepared and characterized. The crystal structure of [LCu(PPh2CH2CH2PPh2)CuL][ClO4]2 has been solved. All complexes exhibit interesting molecular dynamics which could be monitored by 1H NMR spectral characteristics arising from the methylene group of the ligand and also from the protons of the pyrazole part of the ligand in some cases. The complexes with unsymmetric phosphine ligands such as PPhnBu3–n with n = 1 or 2 revealed the presence of two conformations with differing populations as evidenced by temperature dependent 1H NMR spectral data. The thermodynamics of these transformations due to the fluxional character of the ligand, L, has been studied by computer simulations of the experimental spectra. The NMR spectral characteristics revealed that the methylene protons are diastereotropic

Spin-transfer complexes of endohedral metallofullerenes: ENDOR and NMR evidences

The aim of this research was to answer the question whether the area of localization of unpaired electron in a paramagnetic endohedral metallofullerene is restricted by the fullerene shell or a “spin-leakage” beyond the fullerene cage is possible. Herein, we report an ENDOR investigation of La@C₈₂ embedded into the polycarbonate films. The intensive ¹H-ENDOR signal has been revealed. Since the La-EMF does not contain hydrogen atoms, this result testifies to the contact hyperfine interaction of the unpaired electron of La-EMF with the matrix hydrogen atoms, i.e. electron spin density on the polymer protons. We also report a NMR investigation of a liquid solution of the same La-EMF in hexamethylphosphoramide (HMPA), molecules of which contain the NMR active nucleus, phosphorus-31. The paramagnetic shift of the ³¹P NMR signal of bulk HMPA molecules in the presence of La-EMF has been revealed. Thus, much as the charge-transfer complexes, the paramagnetic EMF molecules can form the spin-transfer complexes in which the electron spin density partially localizes beyond the fullerene cage on atoms of the matrix in which the EMF molecules are embedded