Two-Dimensional Dye Self-Assemblies on Graphene: Optical Signature
The field of molecular self-assembly has gone through tremendous advances past years. Starting from simple two-dimensional geometries, the third dimension seems now achievable using molecules like the Janus Tecton(Du P, Bleger D, Charra F, Bouchiat V, Kreher D, Mathevet F, et al. Beilstein J Nanotechnol 6:632–639, 2015; Du P, Jaouen M, Bocheux A, Bourgogne C, Han Z, Bouchiat V, et al. Angew Chem Int Ed 53(38):10060–10066, 2014). Furthermore, recent graphene fabrication process improvements brought a new convenient substrate for self-assemblies (MacLeod M, Rosei F Small 10(6):1038–1049, 2014). Thanks to substrate transfer processes (Li XS, Cai WW, An JH, Kim S, Nah J, Yang DX, et al. Science 324(5932):1312–1314, 2009; Li X, Zhu Y, Cai W, Borysiak M, Han B, Chen D, et al. Nano Lett 9(12):4359–4363, 2009), it is now possible to integrate two-dimensional self-assemblies in various systems, such as nanophotonics devices taking advantage of the graphene transparency. We study the absorption and fluorescence optical properties of six different self-assembled systems on graphene and show that multiple effects have to be considered to explain the optical behavior of these systems. An important red shift and a broadening of the absorption spectrum peaks is observed. We obtain the first fluorescence graphene functionalization taking advantage of the dye quenching dependence with the distance between the dye and the graphene. An estimation of the gain that could be obtained in a plasmonic waveguide shows that two-dimensional self-assemblies may open a new route towards plasmon amplification.