Photodimerization of cinnamate derivatives studied by STM

The photochemical dimerization of two cinnamate derivatives, C18CinnC18 and C18CinnC10, has been investigated at the liquid/graphite interface by scanning tunneling microscopy (STM). The unit cell parameters of the two derivatives as deduced from the STM images indicate that the photodimerization reaction should not occur according to the topochemical postulates. Nevertheless, C18CinnC18 does photodimerize upon irradiation of its monolayer, while C18CinnC10 does not.