Fig. 5
Crystalline structure and optical properties. a Schematic illustration of 2D crystals on different substrates (SiO2 or h-BN). Unlike their bulk counterparts, molecular packing in the first few molecular layers is governed by the competition between the intra-layer interaction (Iintra-layer) and molecule–substrate interaction (Isubstrate). On h-BN, strong Isubstrate leads to a tilted configuration; while on SiO2, weak Isubstrate leads to an approximately freestanding configuration. b The optimized model of p-MSB molecular layers on amorphous SiO2. c PL spectra of p-MSB in solution, p-MSB crystals on h-BN, and SiO2/Si. The right insets are schematic diagrams for the fluorescence mechanism. Excimer-like emission is obtained when the p-MSB molecules are tightly packed in a 2D crystal on SiO2
