Concentration-Independent Stereodynamic g-Probe for Chiroptical Enantiomeric Excess Determination

Enantiomeric excess (ee) determination is crucial in many aspects of science, from synthesis to materials. Within this subject, coupling molecular sensors with chiroptical techniques is a straightforward approach to the stereochemical analysis of chiral molecules, especially in terms of process immediacy and labor. Stereodynamic probes typically consist of racemic mixtures of rapidly interconverting enantiomeric conformers able to recognize a chiral analyte and greatly amplify its chiroptical readout. A great number of sensors have been developed, but their activity is generally restricted to one or a few classes of chemicals, and the analysis outcome relies on precise knowledge of the probe and analyte concentrations. This aspect in particular limits the potential practical applications. Here we report an oxo-vanadium(V) aminotriphenolate complex that was found to act as a concentration-independent stereodynamic sensor for a wide range of compounds. The bare complex is CD-silent, but coordination of an enantioenriched substrate immediately gives rise to intense Cotton effects in the visible region. Furthermore, a geometry change during the substrate-complex interaction leads to a marked optical response, as witnessed by a strong red-shift of the probe absorption bands, thus allowing the generation of dichroic signals in an "interference-free" area of the spectrum. This peculiarity allows for a linear correlation at high wavelengths between the ee of the analyte and anisotropy g-factor. This parameter derives from the differential circularly polarized light absorption of the sample but is independent of concentration. The newly developed sensor based on a simple coordination process has an unprecedented general character in terms of substrate scope and employment.