Two-dimensional electronic spectroscopy of graphene nanoribbons in organic solution Tetsuhiko Nagahara, Lucia Ganzer, V. A. Camargo Franco, Yinjuan Huang, Fugui Xu, Yiyong Mai, Giulio Cerullo and Xinliang Feng EPJ Web Conf., 205 (2019) 05005 Published online: 16 April 2019 DOI: 10.1051/epjconf/201920505005