• Triggering the emission by the helical turn in thiadiazole-helicenes
    Thomas Biet, KÚvin Martin, Jihane Hankache, Nora Hellou, Andreas Hauser, Thomas BŘrgi, Nicolas Vanthuyne, Tal Aharon, Marco Caricato, Jeanne Crassous and Narcis Avarvari
    Chemistry - A European Journal, 23 (2) , 2017, p437-446
    Keywords: chirality;circular dichroism;density functional calculations;helicenes;heterocycles
    DOI:10.1002/chem.201604471 | unige:91450 | Abstract | Article HTML | Article PDF | Supporting Info
Introduction of heterocycles in the helical skeleton of helicenes allows modulation of their redox, chiroptical and photophysical properties. Herein, we describe the straightforward preparation and structural characterization by single crystal X-ray diffraction of thiadiazole-[7]helicene, which has been 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 has been structurally characterized and it shows the presence of both (M) and (P) isomers coordinated to the metal centre. The emission properties of the unprecedented 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 a quenching of the luminescence of enantiopure [7]helicenes through an intersystem crossing mechanism arising from the relaxed excited S1 state.

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Aharon, Tal Avarvari, Narcis Biet, Thomas BŘrgi, Thomas Caricato, Marco 
Crassous, Jeanne Hankache, Jihane Hauser, Andreas Hellou, Nora Martin, KÚvin 
Vanthuyne, Nicolas 
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