Melanins are ubiquitous biopolymers produced from phenols and catechols by oxidation. They provide photoprotection, pigmentation and redox activity to most life forms, and inspire synthetic materials with desirable optical, electronic and mechanical properties. The chemical structures of melanins remain elusive, however, creating uncertainty about their roles, and preventing the design of synthetic mimics with tailored properties. Indole-5,6-quinone (IQ) has been implicated as a biosynthetic intermediate and structural subunit of mammalian eumelanin pigments, but its instability has prevented its isolation and unambiguous characterization. Here we use steric shielding to stabilize IQ and show that ‘blocked’ derivatives exhibit eumelanin’s characteristic ultrafast nonradiative decay and its ability to absorb light from the ultraviolet to the near-infrared. These new compounds are also redox-active and a source of paramagnetism, emulating eumelanin’s unique electronic properties, which include persistent radicals. Blocked IQs are atomistically precise and tailorable molecules that can offer a bottom–up understanding of emergent properties in eumelanin and have the potential to advance the rational design of melanin-inspired materials.

黑色素是无处不在的生物聚合物，由酚类和儿茶酚通过氧化产生。它们为大多数生命形式提供光保护、色素沉着和氧化还原活性，并激发具有理想光学、电子和机械性能的合成材料。然而，黑色素的化学结构仍然难以捉摸，这给它们的作用带来了不确定性，并阻碍了具有定制特性的合成模拟物的设计。Indole-5,6-quinone (IQ) 被认为是哺乳动物真黑色素色素的生物合成中间体和结构亚基，但其不稳定性阻碍了其分离和明确表征。在这里，我们使用空间屏蔽来稳定 IQ，并表明“受阻”衍生物表现出真黑素特有的超快非辐射衰变及其吸收从紫外线到近红外光的能力。这些新化合物还具有氧化还原活性，是顺磁性的来源，模仿了真黑素独特的电子特性，其中包括持久性自由基。Blocked IQs 是原子学上精确且可定制的分子，可以提供对真黑色素涌现特性的自下而上的理解，并有可能推进黑色素启发材料的合理设计。