N‐Arylated 3,5‐Dihydro‐4H‐dinaphtho[2,1‐c:1′,2′‐e]azepines: Axially Chiral Donors with High Helical Twisting Powers for Nonplanar Push–Pull Chromophores |
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Authors: | Brian B. Frank Berta Camafort Blanco Samuel Jakob Fiammetta Ferroni Silvia Pieraccini Dr. Alberta Ferrarini Prof. Dr. Corinne Boudon Prof. Dr. Jean‐Paul Gisselbrecht Dr. Paul Seiler Gian Piero Spada Prof. Dr. François Diederich Prof. Dr. |
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Affiliation: | 1. Laboratorium für Organische Chemie, ETH‐H?nggerberg, HCI, 8093 Zürich (Switzerland), Fax: (+41)?44 632 1109;2. Alma Mater Studiorum–Università di Bologna, Dipartimento di Chimica Organica “A. Mangini“, Via San Giacomo 11, 40126 Bologna (Italy), Fax: (+39)?051 209 5688;3. Dipartimento di Scienze Chimiche, Università di Padova, Via Marzolo, 1, 35131 Padova (Italy);4. Laboratoire d'Electrochimie et de Chimie Physique du Corps Solide, UMR 7177 C.N.R.S, Université de Strasbourg, 4, rue Blaise Pascal, 67000 Strasbourg (France) |
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Abstract: | Axially chiral, N‐arylated 3,5‐dihydro‐4H‐dinaphtho[2,1‐c:1′,2′‐e]azepines have been prepared by short synthetic protocols from enantiopure 1,1′‐bi(2,2′‐naphthol) (BINOL) and anilines. Alkynes substituted with two N‐phenyldinaphthazepine donors readily undergo a formal [2+2] cycloaddition, followed by retro‐electrocyclization, with tetracyanoethene (TCNE) to yield donor‐substituted 1,1,4,4‐tetracyanobuta‐1,3‐dienes (TCBDs) featuring intense intramolecular charge‐transfer (CT) interactions. A dicyanovinyl derivative substituted with one N‐phenyldinaphthazepine donor was obtained by a “one‐pot” oxidation/Knoevenagel condensation from the corresponding propargylic alcohol. Comparative electrochemical, X‐ray crystallographic, and UV/Vis studies show that the electron‐donor qualities of N‐phenyldinaphthazepine are similar to those of N,N‐dimethylanilino residues. The circular dichroism (CD) spectrum of a push–pull chromophore incorporating the chiral donor moiety features Cotton effects of exceptional intensity. With their elongated shape and the rigidity of the chiral N‐aryldinaphthazepine donors, these chromophores are effective inducers of twist distortion in nematic liquid crystals (LCs). Thus, a series of the dinaphthazepine derivatives was used as dopants in the nematic LC E7 (Merck) and high helical twisting powers (β) of the order of hundreds of μm?1 were measured. Theoretical calculations were employed to elucidate the relation between the structure of the dopants and their helical twisting power. For the derivatives with two dinaphthazepine moieties, a strong dependence of the β‐values on the structure and conformation of the linker between them was found. |
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Keywords: | biaryls chirality donor– acceptor systems helical structures liquid crystals |
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