Electronic Structure of Isolated Graphene Nanoribbons in Solution Revealed by Two-Dimensional Electronic Spectroscopy

• Published in: Nano Letters Vol. 24; no. 3; pp. 797 - 804
• Main Authors: Nagahara, Tetsuhiko, Camargo, Franco V. A., Xu, Fugui, Ganzer, Lucia, Russo, Mattia, Zhang, Pengfei, Perri, Antonio, de la Cruz Valbuena, Gabriel, Heisler, Ismael A., D’Andrea, Cosimo, Polli, Dario, Müllen, Klaus, Feng, Xinliang, Mai, Yiyong, Cerullo, Giulio
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 24.01.2024; American Chemical Society (ACS)
• Subjects: graphene nanoribbons; inhomogeneous broadening; two-dimensional electronic spectroscopy; ultrafast spectroscopy; vibronic coupling; inhomogeneous broadening; graphene nanoribbons; vibronic coupling; two-dimensional electronic spectroscopy; ultrafast spectroscopy
• ISSN: 1530-6984; 1530-6992; 1530-6992
• DOI: 10.1021/acs.nanolett.3c02665

Structurally well-defined graphene nanoribbons (GNRs) are nanostructures with unique optoelectronic properties. In the liquid phase, strong aggregation typically hampers the assessment of their intrinsic properties. Recently we reported a novel type of GNRs, decorated with aliphatic side chains, yielding dispersions consisting mostly of isolated GNRs. Here we employ two-dimensional electronic spectroscopy to unravel the optical properties of isolated GNRs and disentangle the transitions underlying their broad and rather featureless absorption band. We observe that vibronic coupling, typically neglected in modeling, plays a dominant role in the optical properties of GNRs. Moreover, a strong environmental effect is revealed by a large inhomogeneous broadening of the electronic transitions. Finally, we also show that the photoexcited bright state decays, on the 150 fs time scale, to a dark state which is in thermal equilibrium with the bright state, that remains responsible for the emission on nanosecond time scales.