Vibrational Circular Dichroism Detects Symmetry Breaking due to Conformational Mobility in C2-Symmetry Chiral Molecules and Provides Further Insight into Inter-Chromophoric Interactions

Abstract

Bicyclo[3.3.1]nonane-2,6-dione (1) and bicyclo[3.3.1]nona-3,7-diene-2,6-dione (2) have been examined by vibrational circular dichroism (VCD), which, as for most C2-symmetric systems, exhibits strong VCD signals. In the case of 2, VCD signals are stronger and sharper with several bisignate doublets; for 1, signals are less intense and broader. The VCD and IR spectra are excellently predicted by DFT calculations: only one conformer is present for 2, while for 1, three main conformers, related through concerted skeleton torsional motions are present (two of them being interchanged by C2-rotation). The VCD spectrum shows specific features for the different conformers, such that correct population factors are crucial for reproducing experimental data. Also, the TD-DFT prediction of ECD (electronic circular dichroism) spectra is good. By comparing the spectroscopic signature of the two molecules (both VCD and ECD) and by careful analysis of the theoretical results, the role of the C=C double bond in compound (2) is evidenced. The double bond contributes toward enhancing the CD response both electronically and vibrationally.

White‐Light Emission and Circularly Polarized Luminescence from a Chiral Copper(I) Coordination Polymer through Symmetry‐Breaking Crystallization

“…Chemie ure S2). [25] These means, after self-assembly, 1-M is more thermodynamically stable than 1-P and is probably preferred in the primary nucleation process. Experiments were further conducted to confirm this inference.…”

“…The results show that the C 2 ‐symmetric flask‐shaped loop in 1‐M is more stable than that in 1‐P , whose energetic value is 113.99 kcal mol −1 smaller than that of 1‐P (Table S3). Meanwhile, the relative stabilities of Hptdp in the two enantiomers were also evaluated, showing little difference (Table S4 and Figure S2) [25] . These means, after self‐assembly, 1‐M is more thermodynamically stable than 1‐P and is probably preferred in the primary nucleation process.…”

White‐Light Emission and Circularly Polarized Luminescence from a Chiral Copper(I) Coordination Polymer through Symmetry‐Breaking Crystallization

“…). [25] These means, after self-assembly, 1-M is more thermodynamically stable than 1-P and is probably preferred in the primary nucleation process. Experiments were further conducted to confirm this inference.…”