wing to their width-dependent sizable band gaps, graphene nanoribbons (GNRs) have attracted increasing attention in the last decade as a viable route for graphene-based nano- and opto-electronic applications. More recently, the successful production of ultranarrow and structurally well-defined GNRs by means of bottom-up techniques has further boosted this research line.
Here, I will present our recent work on the optical properties of GNRs, as resulting from state-of-the-art ab initio calculations, and compare them with experimental data from different optical spectroscopies. We show that the extreme quantum confinement leads to linear and non-linear optical spectra dominated by strong multi-particle excitations (i.e. excitons and biexcitons) [1,2], whose energy position is significantly influenced by both edge morphology and functionalization. Substrate effects are unravelled by means of many-body perturbation theory simulations and model approaches [1,3]. Finite size effects and below-bandgap light emission are rationalized and compared with STS measurements of suspended GNRs .
 Exciton-dominated optical response of ultra-narrow graphene nanoribbons, R. Denk et al., Nat. Commun. 5, 4253 (2014)
 Exciton-exciton annihilation and biexciton stimulated emission in graphene nanoribbons, G. Soavi et al., Nat. Commun. 7, 11010 (2016)
 Electronic structure of atomically precise graphene nanoribbons, P. Ruffieux et. al., ACS Nano 6, 6930 (2012)
 Bright electroluminescence from single graphene nanoribbon junctions, M. Chong et al., preprint (2017).