Physicochemical and Electronic Properties of Cationic [6]Helicenes: from Chemical and Electrochemical Stabilities to Far-Red (Polarized) Luminescence.

ABSTRACT: 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 (pKR+ =20.4, Ered1/2 =-0.72?V) compared to its azaoxa 2 (pKR+ =15.2, Ered1/2 =-0.45?V) and dioxa 1 (pKR+ =8.8, Ered1/2 =-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.

SUBMITTER: Bosson J 

PROVIDER: S-EPMC5396952 | biostudies-literature | 2016 Dec

REPOSITORIES: biostudies-literature