Nanographenes (NGs) and graphene nanoribbons (GNRs) are molecular-level bridges to bulk-carbon materials. When synthesized with atomic precision via, for example, bottom-up strategies, a direct connection between the structure and properties is demonstrable. This is of key interest, especially considering practical applications. In the current work, we report the synthesis and comprehensive photophysical characterization of a full-benzenoid nanographene (NG-Br) and its covalent conjugate featuring a porphyrin (NG-(Zn)Por). Our synthetic approach relies on a cascade of Suzuki coupling, reduction, and Sandmeyer bromination reactions, starting from halogenated nitrobenzene derivatives. Knowing at which concentration aggregation occurs is important to study either monomers of NG-Br or its aggregates. In organic solvents, the association constant of NG-Br exceeds 1 × 106 M–1. Photophysical and theoretical analyses on the monomer revealed a subtle energy proximity between (S1)/(Lb) and (S2)/(La) that is the basis for strong vibronic coupling via the Herzberg–Teller mechanism, as well as (S1,1) and (S2,0) vibronic mixing. In NG-(Zn)Por, an ultrafast (S1–S1) energy transfer from NG to the porphyrin was observed. Our findings are essential for establishing an unambiguous structure–property relationship for NGs and 9-armchair GNRs, providing a blueprint for their use in optoelectronic devices ranging from single-electron transistors to OLEDs and organic solar cells.

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.

Momentan verbrennen wir noch große Mengen fossiler Energieträger wie Erdöl oder Kohle, um unseren Energiehunger zu stillen. Dabei entsteht das Treibhausgas Kohlendioxid, das in der Atmosphäre wie eine...