Cu(I/II) Redox Control of Molecular Conformation and Shape in Chiral Tripodal Ligands:  Binary Exciton-Coupled Circular Dichroic States

Abstract

This manuscript describes the design, synthesis, and characterization of a coordination complex that demonstrates reversible interconversion between two redox states that show very different chiroptical properties. Reported here are three chiral N(4)-tetradentate ligands, prepared in enantiopure form by asymmetric synthesis, and their circular dichroic and other properties, as well as those of numerous Cu(I) and Cu(II) complexes. While the chiroptical spectra of the free ligands are unremarkable, the CD spectra of the complexes are very intense, and spectral features indicate that they derive from exciton coupling. Comparison of complexes with one, two, or three chromophores provides strong supportive evidence for this assignment, and semiquantitative correlation with intensity as rationalized by additivity. A Cu(I)(L)/Cu(II)(L) redox couple was identified that showed dramatically different circular dichroic properties that was further shown to be easily oxidized and reduced chemically between two states with remarkable retention of signal. A structural hypothesis for the interconversion is given and supported by a variety of spectroscopic evidence.

Transition metal-based chiroptical switches for nanoscale electronics and sensors

“…The overall effect is a very large difference in ECCD amplitude between Cu(I) and Cu(II) states. Dependence of the ECCD amplitude on the counter ion supported the structural assignment [68]. The complex is highly reversible chemically upon oxidation of the Cu(I) complex with ammonium persulfate and reduction of the Cu(II) complex with sodium ascorbate.…”

Asymmetry and steric hindrance in tripodal ligands: Reaching the limit for octahedral geometry with the newly synthesized [(6-bromo 2-pyridylmethyl) (6-fluoro 2-pyridylmethyl) (2-pyridylmethyl)] amine tripod in FeCl2 complexes

“…1 H NMR data were collected in CD 3 CN solutions (or CDCl 3 for the free ligands) on a Bruker AC 300 spectrometer at 300.1300 MHz using the residual signal of CD 2 HCN (CHCl 3 for ligand) as a reference for calibration. 13 C data were collected on the same spectrometer at 75.4867 MHz, using the same calibration procedure. 19 F data were also collected on the same spectrometer at 282.4037 MHz, and calibrated with CFCl 3 .…”

“…Tetradentate tripods derived from the tris(2-pyridylmethyl)amine (TPA) are among the most thoroughly studied with a broad range of potential applications [3][4][5][6][7]. The introduction of asymmetric centres by substitution at the methylene carbon has been reported for several years, allowing extension of the chemistry of these simple ligands to various areas (asymmetric recognition of amino acids, study of chiropticalor luminescence properties to cite only a few of them) [7][8][9][10][11][12][13]. In an other perspective, asymmetrical substitution of all the a position of the pyridyl units would represent a more straightforward modification of the reactivity site, i.e.…”

A stereodynamic tripodal ligand with three different coordinating arms: Synthesis and zinc(II), copper(I) complexation study

“…The chiral carbon center biases the propeller-like conformation, fixing the orientation of the confined arms and resulting in the coupling of the chromophores and leading to strong exciton-coupled circular dichroism (ECCD) signals (Figure 1). 14…”