Absorption and fluorescence were investigated for liquid-crystalline discotics, which are characterized by the spontaneous formation of one-dimensional columnar structures in the fluid phase. Such materials have been considered for applications in organic light-emitting diodes and as photoconductors. We investigated materials based on asymmetrically substituted triphenylenes displaying a novel highly ordered plastic columnar state. These materials show an unexpected time dependence of the fluorescence spectrum during irradiation apparently because of their specific spatial structure. Transfer of energy from a high-energy excited state to a newly developing lower-energy state takes place. We attribute the evolution of this state to the particular spatial arrangement of the molecules within the columns in the plastic columnar state. This causes the photoinduced formation of dimers, a process that is absent in solutions and in polymer-dispersed systems of discotic materials and that has, so far, not been documented in the literature.