Conformational Study Of An Axially Chiral Salen Ligand In Solution Using Two-Photon Circular Dichroism And The Fragment-Recombination Approach

Herein we report on the conformational study of a chiral Salen ligand, AFX-155, in THF solution using two-photon absorption (TPA) and, even more importantly, two-photon circular dichroism (TPCD). The fragment-recombination approach (FRA), employed to perform computations on half-AXF-155 (AXF-169′) and the center (C-AXF-155), allowed us to overcome the current computational limitations found in calculations of the TPCD spectra of large molecules. The comparative experimental-theoretical analysis of AXF-155 showed that its TPA is mainly determined by AXF-169′ and validated, through TPCD, the presence of the two dominant Trans-R-Intra(NHB)//Trans-R-Extra(HB) and Trans-R-Intra(NHB)//Trans-R-Extra(NHB) structure in THF with a ΔΔ propeller chirality on the diphenylamine moieties at the end of each AXF-169′. The application of FRA for the analysis of the TPCD spectra of large chiral molecules has been proven to be effective. © 2013 American Chemical Society