title: 1,2-Di(phenylethynyl)ethenes with axially chiral, 2,2'-bridged 1,1'-binaphthyl substituents: potent cholesteric liquid-crystal inducers.
abstract: Axially chiral, 3,5-dihydro-4H-dinaphtho[2,1-c:1',2'-e]azepine (dinaphthazepine) and 1,1'-binaphthyl-2,2'-disulfonimide (dinaphthosulfonimide) moieties were rigidly connected via N-p-phenylene linkers to photochemically (E)/(Z)-isomerisable 1,2-diethynylethene scaffolds. The chemical stability of the resulting systems was found to be critically related to the other substituents on the central π-conjugated scaffold. High helical twisting power (HTP), up to 315 μm(-1), for the induction of a cholesteric liquid-crystalline phase through doping of a nematic phase was measured, resulting from the introduction of the chiral, mesogenic 1,1'-binaphthyl motifs. Single crystal X-ray analysis revealed that the phenylene spacer is in π-conjugation with the N-atom of the dinaphthazepine but not with the N-atom of the dinaphthosulfonimide moiety. This difference in orientation results in visible-transparency in the electronic absorption spectrum and higher (E)/(Z)-photoisomerisation quantum yields of the dinaphthosulfonimide-derived chiral dopants, as compared to the dinaphthazepine systems, which feature intramolecular charge-transfer absorption in the visible region.
authors.affiliation: Laboratorium für Organische Chemie, ETH Zürich, Hönggerberg, HCI, CH-8093 Zürich, Switzerland.
authors.forename: Yi-Lin
authors.initials: YL
authors.lastname: Wu
authors.forename: Fiammetta
authors.initials: F
authors.lastname: Ferroni
authors.forename: Silvia
authors.initials: S
authors.lastname: Pieraccini
authors.forename: W Bernd
authors.initials: WB
authors.lastname: Schweizer
authors.forename: Brian B
authors.initials: BB
authors.lastname: Frank
authors.forename: Gian Piero
authors.initials: GP
authors.lastname: Spada
authors.forename: François
authors.initials: F
authors.lastname: Diederich
mesh_terms: D000475:Alkenes / Q000737:chemistry*; D000480:Alkynes / Q000737:chemistry*; D002784:Cholesterol / Q000138:chemical synthesis / Q000737:chemistry*; D018360:Crystallography, X-Ray; D050866:Liquid Crystals / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D009281:Naphthalenes / Q000737:chemistry*
chemical_list: D000475:Alkenes; D000480:Alkynes; D009281:Naphthalenes; D002784:Cholesterol; C412330:1,1'-binaphthyl