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

摘要

Physicochemical properties of cationic dioxa >1, azaoxa >2 and diaza >3 [6]helicenes demonstrate a much higher chemical stability of diaza adduct >3 (pKR+ 20.4, E1/2red −0.72 V) compared to azaoxa >2 (pKR+ 15.2, E1/2red −0.45 V) and dioxa >1 (pKR+ 8.8, E1/2red −0.12 V) analogues. The fluorescence of these cationic chromophores was 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 at 658 nm) are observed. The triplet quantum yields and the circularly polarized luminescence are also reported. Finally, fine tuning of the optical properties of the diaza [6]helicene core was achieved through selective and orthogonal post-functionalization reactions (12 examples, compounds >4->15). The electronic absorption is modulated from the orange to far-red spectral range (560-731 nm) while 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.