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Helitwistacenes-Combining Lateral and Longitudinal Helicity Results in Solvent-Induced Inversion of Circularly
Israa Shioukhi1, Harikrishna Batchu1, Gal Schwartz2
1Institute of Chemistry and the Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Edmond J. Safra Campus, 9190401, Jerusalem, Israel.
Angewandte Chemie (International Ed. in English)
|January 15, 2024
Summary
Helicity in fused acenes differs between helicenes and twistacenes. Combining them into helitwistacenes shows that twistacene helicity influences electronic spectra, causing solvent-induced sign inversion.
Area of Science:
- Organic Chemistry
- Supramolecular Chemistry
- Spectroscopy
Background:
- Helicity in fused acenes manifests distinctly in helicenes and twistacenes.
- Helicenes exhibit constant helicity, while twistacenes offer tunable helicity and handedness, often influenced by helicenes.
Purpose of the Study:
- To synthesize and characterize novel helitwistacene molecules by combining helicenes and rigid twistacenes.
- To investigate the impact of combining these units on molecular helicity and chiroptical properties.
Main Methods:
- X-ray crystallography to determine structural integrity.
- Electronic Circular Dichroism (ECD) and Circularly Polarized Luminescence (CPL) spectroscopy to analyze chiroptical properties.
- ROESY NMR and Time-Dependent Density Functional Theory (TD-DFT) calculations for structural and electronic insights.
Main Results:
- X-ray structures confirm that the linkage preserves the helicity of individual helicene and twistacene units.
- ECD and CPL spectra are significantly modulated by the twistacene unit's helicity.
- Solvent-induced sign inversion observed in chiroptical spectra.
- Observed phenomena attributed to altered relative orientations between helicene and twistacene moieties.
Conclusions:
- Helitwistacenes represent a new class of molecules where combined helicity influences chiroptical behavior.
- The twistacene moiety plays a crucial role in dictating the electronic response and spectral characteristics.
- Understanding these structure-property relationships is key for designing advanced chiral materials.
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