title: Triggering Emission with the Helical Turn in Thiadiazole-Helicenes.
abstract: Introduction of heterocycles into the helical skeleton of helicenes allows modulation of their redox, chiroptical, and photophysical properties. This paper describes the straightforward preparation and structural characterization by single-crystal X-ray diffraction of thiadiazole-[7]helicene, which was resolved into M and P enantiomers by chiral HPLC, together with its S-shaped double [4]helicene isomer, as well as the smaller congeners thiadiazole-[5]helicene and benzothiadiazole-anthracene. A copper(II) complex with two thiadiazole-[5]helicene ligands was structurally characterized, and it shows the presence of both M and P isomers coordinated to the metal center. The emission properties of the heterohelicenes are highly dependent on the helical turn, as the [7]- and [5]helicene are poorly emissive, whereas their isomers, that is, the S-shaped double [4]helicene and thiadiazole-benzanthracene, are luminescent, with quantum efficiencies of 5.4 and 6.5 %, respectively. DFT calculations suggest quenching of the luminescence of enantiopure [7]helicenes through an intersystem-crossing mechanism arising from the relaxed excited S1 state.
authors.affiliation: Université d'Angers, CNRS UMR 6200, Laboratoire MOLTECH-Anjou, 2 bd Lavoisier, 49045, Angers, France.
authors.forename: Thomas
authors.initials: T
authors.lastname: Biet
authors.affiliation: Université d'Angers, CNRS UMR 6200, Laboratoire MOLTECH-Anjou, 2 bd Lavoisier, 49045, Angers, France.
authors.forename: Kévin
authors.initials: K
authors.lastname: Martin
authors.affiliation: Department of Physical Chemistry, University of Geneva, 30 Quai Ernest Ansermet, 1211, Geneva, Switzerland.
authors.forename: Jihane
authors.initials: J
authors.lastname: Hankache
authors.affiliation: Institut des Sciences Chimiques de Rennes, UMR 6226, CNRS - Université de Rennes 1, Campus de Beaulieu, 35042, Rennes Cedex, France.
authors.forename: Nora
authors.initials: N
authors.lastname: Hellou
authors.affiliation: Department of Physical Chemistry, University of Geneva, 30 Quai Ernest Ansermet, 1211, Geneva, Switzerland.
authors.forename: Andreas
authors.initials: A
authors.lastname: Hauser
authors.affiliation: Department of Physical Chemistry, University of Geneva, 30 Quai Ernest Ansermet, 1211, Geneva, Switzerland.
authors.forename: Thomas
authors.initials: T
authors.lastname: Bürgi
authors.affiliation: Aix Marseille Univ, CNRS, Centrale Marseille, iSm2, Marseille , France.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Vanthuyne
authors.affiliation: Department of Chemistry, University of Kansas, 1251 Wescoe Hall Drive, Lawrence, Kansas, 66045, USA.
authors.forename: Tal
authors.initials: T
authors.lastname: Aharon
authors.affiliation: Department of Chemistry, University of Kansas, 1251 Wescoe Hall Drive, Lawrence, Kansas, 66045, USA.
authors.forename: Marco
authors.initials: M
authors.lastname: Caricato
authors.affiliation: Institut des Sciences Chimiques de Rennes, UMR 6226, CNRS - Université de Rennes 1, Campus de Beaulieu, 35042, Rennes Cedex, France.
authors.forename: Jeanne
authors.initials: J
authors.lastname: Crassous
authors.affiliation: Université d'Angers, CNRS UMR 6200, Laboratoire MOLTECH-Anjou, 2 bd Lavoisier, 49045, Angers, France.
authors.forename: Narcis
authors.identifier: 0000-0001-9970-4494
authors.initials: N
authors.lastname: Avarvari
keywords: chirality; circular dichroism; density functional calculations; helicenes; heterocycles