11. Triple para-Functionalized Cations and Neutral Radicals of Enantiopure Diaza [4]Helicenes
    Fabri, B.; Funaioli, T.; Frédéric, L.; Elsner, C.; Bordignon, E.; Zinna, F.; Di Bari, L.; Pescitelli, G.; Lacour, J.
    J. Am. Chem. Soc. 2024, 146, 8308-8319

Modulation of absorbance and emission is key for the design of chiral chromophores. Accessing a series of compounds absorbing and emitting (circularly polarized) light over a wide spectral window, and often toward near infrared, is of practical value in (chir)optical applications. Herein, by late-stage functionalization on derivatives bridging triaryl methyl and helicene domains, we have achieved the regioselective triple introduction of para electron-donating or electron-withdrawing substituents. Extended tuning of electronic (e.g., E_1/2^red –1.50 V → –0.68 V) and optical (e.g., emission covering from 550 to 850 nm) properties is achieved for the cations and neutral radicals; the latter compounds being easily prepared by mono electron reductions under electrochemical or chemical conditions. While luminescence quantum yields can be increased up to 70% in the cationic series, strong Cotton effects are obtained for certain radicals at low energies (λ_abs ~ 700-900 nm) with g_abs values above 10^-3. The open-shell electronic nature of the radicals was further characterized by EPR revealing an important spin density delocalization that contributes to their persistence

DOI : 10.1021/jacs.3c13487 

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