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Triggering Emission with the Helical Turn in Thiadiazole‐Helicenes
Author(s) -
Biet Thomas,
Martin Kévin,
Hankache Jihane,
Hellou Nora,
Hauser Andreas,
Bürgi Thomas,
Vanthuyne Nicolas,
Aharon Tal,
Caricato Marco,
Crassous Jeanne,
Avarvari Narcis
Publication year - 2017
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201604471
Subject(s) - helicene , enantiopure drug , chemistry , quenching (fluorescence) , enantiomer , luminescence , anthracene , intersystem crossing , crystallography , photochemistry , excited state , stereochemistry , materials science , molecule , fluorescence , organic chemistry , enantioselective synthesis , optoelectronics , optics , physics , nuclear physics , singlet state , catalysis
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.