- Synthesis, Resolution, Configurational Stability, and Properties of Cationic Functionalized Helicenes
Maya Marinova, Simon Pascal, Laure Guénée, Céline Besnard, Boris Shivachev, Kalina Kostova, Claudio Villani, Roberta Franzini, Vladimir Dimitrov, Jérôme Lacour
J. Org. Chem. 2020, 85, 11908-11923
A straightforward approach to the synthesis of two different series of cationic 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 redshift 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 HPLC resolution or, when configurational lability was too high, through VT-HPLC analysis on chiral stationary phase (ΔG‡ values ranging from 85.0 to 137.1 kJ.mol-1 and above).
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