Synthesis and fluorescence properties of DMCX+—a stable oxygen-bridged [4]helicenium dye

Synthesis, Resolution, Configurational Stability, and Properties of Cationic Functionalized [5]Helicenes

A straightforward approach to the synthesis of two different series of cationic [5]helicenes has been achieved including, in dioxa series, the possibility to introduce aromatic functional groups at the periphery of the helical structure. While photophysical study highlights that the introduction of aryl substituents at position 23 of the helical moieties has a negligible impact on the optical properties, styryl substituents allow a welcoming extension of the conjugation pathways. Finally, a red shift of the optical properties was evidenced upon introduction of nitrogen atoms in the helicene scaffold, leading to particularly good fluorescence efficiencies in the red domain for a helicenic dye. Detailed information on racemization kinetics was collected for the most stable species upon direct high-performance liquid chromatography (HPLC) resolution or, when configurational lability was too high, through VT-HPLC analysis on the chiral stationary phase (ΔG^‡ values ranging from 85.0 to 137.1 kJ·mol^-1 and above).

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

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.

Cationic triangulenes and helicenes: synthesis, chemical stability, optical properties and extended applications of these unusual dyes

Cationic triangulenes and helicenes are highly stable carbocations with planar and helical conformations respectively. These moieties are effective dyes with original absorption and emission properties. Over the last decade, they have received greater attention and are considered as valuable tools for the development of innovative applications. In this review, the synthesis of these unique compounds is presented together with their core chemical and physical properties. Representative applications spanning from surface sciences to biology and chemistry are presented.