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Physicochemical and Electronic Properties of Cationic [6]Helicenes: from Chemical and Electrochemical Stabilities to Far‐Red (Polarized) Luminescence
Author(s) -
Bosson Johann,
Labrador Geraldine M.,
Pascal Simon,
Miannay FrançoisAlexandre,
Yushchenko Oleksandr,
Li Haidong,
Bouffier Laurent,
Sojic Neso,
Tovar Roberto C.,
Muller Gilles,
Jacquemin Denis,
Laurent Adèle D.,
Le Guennic Boris,
Vauthey Eric,
Lacour Jérôme
Publication year - 2016
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.201603591
Subject(s) - cationic polymerization , luminescence , electrochemistry , far red , chemistry , materials science , photochemistry , optoelectronics , red light , organic chemistry , electrode , biology , botany
The physicochemical properties of cationic dioxa ( 1 ), azaoxa ( 2 ), and diaza ( 3 ) [6]helicenes demonstrate a much higher chemical stability of the diaza adduct 3 (p K R + =20.4, E red1 / 2=−0.72 V) compared to its azaoxa 2 (p K R + =15.2, E red1 / 2=−0.45 V) and dioxa 1 (p K R + =8.8, E red1 / 2=−0.12 V) analogues. The fluorescence of these cationic chromophores is established, and ranges from the orange to the far‐red regions. From 1 to 3 , a bathochromic shift of the lowest energy transitions (up to 614 nm in acetonitrile) and an enhancement of the fluorescence quantum yields and lifetimes (up to 31 % and 9.8 ns, respectively, at 658 nm) are observed. The triplet quantum yields and circularly polarized luminescence are also reported. Finally, fine tuning of the optical properties of the diaza [6]helicene core is achieved through selective and orthogonal post‐functionalization reactions (12 examples, compounds 4 – 15 ). The electronic absorption is modulated from the orange to the far‐red spectral range (560–731 nm), and fluorescence is observed from 591 to 755 nm with enhanced quantum efficiency up to 70 % (619 nm). The influence of the peripheral auxochrome substituents is rationalized by first‐principles calculations.