Chemical reduction of a benzo‐fused double [7]helicene (
- Award ID(s):
- 1855470
- NSF-PAR ID:
- 10346707
- Date Published:
- Journal Name:
- Chemical Communications
- Volume:
- 57
- Issue:
- 82
- ISSN:
- 1359-7345
- Page Range / eLocation ID:
- 10743 to 10746
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract 1 ) with two alkali metals, K and Rb, provided access to three different reduced states of1 . The doubly‐reduced helicene1 2−has been characterized by single‐crystal X‐ray diffraction as a solvent‐separated ion triplet with two potassium counterions. The triply‐ and tetra‐reduced helicenes,1 3−and1 4−, have been crystallized together in an equimolar ratio and both form the contact‐ion complexes with two Rb+ions each, leaving three remaining Rb+ions wrapped by crown ether and THF molecules. As structural consequence of the stepwise reduction of1 , the central axis of helicene becomes more compressed upon electron addition (1.42 Å in1 4−vs. 2.09 Å in1 ). This is accompanied by an extra core twist, as the peripheral dihedral angle increases from 16.5° in1 to 20.7° in1 4−. Theoretical calculations provided the pattern of negative charge build‐up and distribution over the contorted helicene framework upon each electron addition, and the results are consistent with the X‐ray crystallographic and NMR spectroscopic data. -
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Abstract Chemical reduction of a benzo‐fused double [7]helicene (
1 ) with two alkali metals, K and Rb, provided access to three different reduced states of1 . The doubly‐reduced helicene1 2−has been characterized by single‐crystal X‐ray diffraction as a solvent‐separated ion triplet with two potassium counterions. The triply‐ and tetra‐reduced helicenes,1 3−and1 4−, have been crystallized together in an equimolar ratio and both form the contact‐ion complexes with two Rb+ions each, leaving three remaining Rb+ions wrapped by crown ether and THF molecules. As structural consequence of the stepwise reduction of1 , the central axis of helicene becomes more compressed upon electron addition (1.42 Å in1 4−vs. 2.09 Å in1 ). This is accompanied by an extra core twist, as the peripheral dihedral angle increases from 16.5° in1 to 20.7° in1 4−. Theoretical calculations provided the pattern of negative charge build‐up and distribution over the contorted helicene framework upon each electron addition, and the results are consistent with the X‐ray crystallographic and NMR spectroscopic data. -
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Abstract The chemical reduction of π‐conjugated bilayer nanographene
1 (C138H120) with K and Rb in the presence of 18‐crown‐6 affords [K+(18‐crown‐6)(THF)2][{K+(18‐crown‐6)}2(THF)0.5][C138H1223−] (2 ) and [Rb+(18‐crown‐6)2][{Rb+(18‐crown‐6)}2(C138H1223−)] (3 ). Whereas K+cations are fully solvent‐separated from the trianionic core thus affording a “naked”1.3 −anion, Rb+cations are coordinated to the negatively charged layers of1.3 −. According to DFT calculations, the localization of the first two electrons in the helicene moiety leads to an unprecedented site‐specific hydrogenation process at the carbon atoms located on the edge of the helicene backbone. This uncommon reduction‐induced site‐specific hydrogenation provokes dramatic changes in the (electronic) structure of1 as the helicene backbone becomes more compressed and twisted upon chemical reduction, which results in a clear slippage of the bilayers. -
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Abstract The chemical reduction of π‐conjugated bilayer nanographene
1 (C138H120) with K and Rb in the presence of 18‐crown‐6 affords [K+(18‐crown‐6)(THF)2][{K+(18‐crown‐6)}2(THF)0.5][C138H1223−] (2 ) and [Rb+(18‐crown‐6)2][{Rb+(18‐crown‐6)}2(C138H1223−)] (3 ). Whereas K+cations are fully solvent‐separated from the trianionic core thus affording a “naked”1.3 −anion, Rb+cations are coordinated to the negatively charged layers of1.3 −. According to DFT calculations, the localization of the first two electrons in the helicene moiety leads to an unprecedented site‐specific hydrogenation process at the carbon atoms located on the edge of the helicene backbone. This uncommon reduction‐induced site‐specific hydrogenation provokes dramatic changes in the (electronic) structure of1 as the helicene backbone becomes more compressed and twisted upon chemical reduction, which results in a clear slippage of the bilayers. -
null (Ed.)While the development of chiral molecules displaying circularly polarized luminescence (CPL) has received considerable attention, the corresponding CPL intensity, g lum, hardly exceeds 10 −2 at the molecular level owing to the difficulty in optimizing the key parameters governing such a luminescence process. To address this challenge, we report here the synthesis and chiroptical properties of a new family of π-helical push–pull systems based on carbo[6]helicene, where the latter acts as either a chiral electron acceptor or a donor unit. This comprehensive experimental and theoretical investigation shows that the magnitude and relative orientation of the electric ( μe ) and magnetic (μ m ) dipole transition moments can be tuned efficiently with regard to the molecular chiroptical properties, which results in high g lum values, i.e. up to 3–4 × 10 −2 . Our investigations revealed that the optimized mutual orientation of the electric and magnetic dipoles in the excited state is a crucial parameter to achieve intense helicene-mediated exciton coupling, which is a major contributor to the obtained strong CPL. Finally, top-emission CP-OLEDs were fabricated through vapor deposition, which afforded a promising g El of around 8 × 10 −3 . These results bring about further molecular design guidelines to reach high CPL intensity and offer new insights into the development of innovative CP-OLED architectures.more » « less
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D1CC03314J
