Intramolecular Singlet Fission in Individual Graphene Nanoribbons─Competition with a Charge Transfer,Journal of the American Chemical Society

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Intramolecular Singlet Fission in Individual Graphene Nanoribbons─Competition with a Charge Transfer
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2025-03-19 , DOI: 10.1021/jacs.4c18051
Phillip M Greißel ₁ , Giovanni M Beneventi ₁ , René Weiß ₁ , Anna-Sophie Wollny ₁ , Rajeev K Dubey ₂ , Manuel Melle-Franco ₃ , Timothy Clark ₄ , Aurelio Mateo-Alonso _{2,

5} , Dirk M Guldi ₁

Affiliation

Graphene nanoribbons (NRs) constitute a versatile platform for developing novel materials, where their structure governs their optical, electronic, and magnetic properties while also shaping their excited-state dynamics. Here, we investigate a set of three twisted N-doped molecular NRs of increasing length, obtained by linearly fusing perylene diimide to pyrene and pyrazino- or thiadiazolo-quinoxaline residues. By employing various temperature-dependent time-resolved spectroscopy techniques, we reveal how the flexible twisted NR geometry promotes the formation of a mixed electronic state with varying contributions from locally excited and charge-transfer (CT) states. The fate of this mixed state is highly sensitive to the molecular geometry, length, and solvent polarity. For the shortest NR, intersystem crossing dominates the deactivation pathway, efficiently generating triplets in low-polarity solvents. In contrast, for the extended NRs, intramolecular singlet fission (SF) takes place within a single nanoribbon. This is enabled by enhanced superexchange coupling due to a pronounced push–pull nature and the existence of multiple localized π-electron states caused by heteroatom doping, thereby circumventing the need for dimeric interactions typically associated with conventional SF systems. In higher-polarity environments, evidence of a (diabatic) CT state emerges. These findings underscore the intricate relationship between geometry, energy levels, and excited-state dynamics in twisted N-doped NRs.

中文翻译：

单个石墨烯纳米带中的分子内单线态裂变 - 电荷转移的竞争

石墨烯纳米带（NR）构成了开发新型材料的多功能平台，其结构控制着它们的光学、电子和磁性，同时也塑造了它们的激发态动力学。在这里，我们研究了一组三个长度递增的扭曲 N 掺杂分子 NRs，它们是通过将苝二酰亚胺线性熔合到芘和吡嗪基或噻二唑并喹喔啉残基中获得的。通过采用各种与温度相关的时间分辨光谱技术，我们揭示了柔性扭曲 NR 几何形状如何促进混合电子态的形成，以及局部激发和电荷转移（CT）态的不同贡献。这种混合态的命运对分子几何形状、长度和溶剂极性高度敏感。对于最短的 NR，系统间交叉在失活途径中占主导地位，在低极性溶剂中有效地产生三联体。相比之下，对于扩展的 NR，分子内单线态裂变（SF）发生在单个纳米带内。这是通过增强的超交换耦合实现的，这是由于明显的推拉性质和杂原子掺杂引起的多个局域π电子态的存在，从而规避了通常与传统 SF 系统相关的二聚体相互作用的需求。在高极性环境中，会出现（非绝热）CT 状态的证据。这些发现强调了扭曲 N 掺杂 NR 中的几何形状、能级和激发态动力学之间的复杂关系。

更新日期：2025-03-19

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