A direct observation on the surface assembling and ordering of coumarin derivatives on the graphite surface

The 2D monolayer structures of two coumarin derivatives, 4-heptadecyl-7-hydroxycoumarin (HHC) 1 and 3-(2-benzo thiazolyl)-7-octadecyloxy-coumarin (BOC) 2, have been studied by STM and different sensitivity to thermal annealing for these two systems has been observed. The results show that the arrangements of these two molecules are obviously different in the self-assembled monolayer at 20 °C on the graphite surface. Furthermore, only BOC is sensitive to thermal annealing. The assembly of BOC becomes more stable and ordered after annealing at 65 °C for 1 h.