Combined Experimental and Theoretical Studies on Planar Chirality of Partially Overlapped <i>C</i>₂-Symmetric [3.3](3,9)Dicarbazolophanes

Abstract

Partially overlapped dicarbazolophanes exhibit a planar chirality. In this study, <i>C</i>₂-symmetrical [3.3](3,9)dicarbazolophane derivatives (<b>CZ1</b>-<b>CZ3</b>) have been optically resolved by preparative chiral high-performance liquid chromatography for the first time. In their circular dichroism (CD) spectra, moderate Cotton effects (CEs) were observed for their ¹L_b and ¹L_a transitions (|Δε| = 10-12 and 51-57 M^-1 cm^-1, respectively), while intense CEs were notified in their ¹B transitions (|Δε| = 156-216 M^-1 cm^-1), absorption dissymmetry (<i>g</i>_abs) factors being in orders of 10^-2. Circularly polarized luminescence spectrum was also obtained for cyanamide derivative <b>CZ1</b>, with a comparative luminescence dissymmetry (<i>g</i>_lum) factor of 0.013. A computational investigation was applied to address the factors for such remarkable chiroptical responses in these dicarbazolophanes of planar chirality. Absolute configurations were unambiguously determined by the comparison of experimental and theoretical CD spectra, which was affirmed by the X-ray crystal structural analysis of enantiomerically pure sulfonamide derivative <b>CZ2</b>.