Triple <i>para</i>-Functionalized Cations and Neutral Radicals of Enantiopure Diaza[4]helicenes

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., E1/2red −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 (λabs ∼ 700–900 nm) with gabs values above 10–3. The open-shell electronic nature of the radicals was further characterized by electron paramagnetic resonance revealing an important spin density delocalization that contributes to their persistence.吸光度与发射的调控是手性生色团（chiral chromophores）设计的核心要点。构建一系列可在宽光谱窗口内吸收并发射圆偏振光（circularly polarized light）、且通常可覆盖近红外区域的化合物，在（手性）光学应用中具备极高的实用价值。在此工作中，我们通过对桥连三芳基甲基与螺烯结构域的衍生物进行后期官能化修饰，成功实现了对位给电子取代基或吸电子取代基的区域选择性三取代。我们对阳离子及中性自由基的电子性质（如还原半波电位从-1.50 V 调整至-0.68 V）与光学性质（如发射波长覆盖550至850 nm）进行了大范围调控；这类中性自由基可通过电化学或化学条件下的单电子还原轻松制备。在阳离子系列中，发光量子产率最高可提升至70%；而部分自由基在低能吸收区（λabs ≈700–900 nm）可产生较强的科顿效应（Cotton effects），其吸收各向异性因子gabs值高于10⁻³。我们进一步通过电子顺磁共振（electron paramagnetic resonance）对自由基的开壳层电子结构进行了表征，结果显示其存在显著的自旋密度离域现象，这也是这类自由基能够稳定存在的重要原因。