Time-resolved fluorescence in 3-dimensional ordered columnar discotic materials

Absorption and fluorescence were investigated for liquid-crystalline discot ics, which are characterized by the spontaneous formation of one-dimensiona l columnar structures in the fluid phase. Such materials have been consider ed for applications in organic light-emitting diodes and as photoconductors . We investigated materials based on asymmetrically substituted triphenylen es displaying a novel highly ordered plastic columnar state. These material s show an unexpected time dependence of the fluorescence spectrum during ir radiation apparently because of their specific spatial structure. Transfer of energy from a high-energy excited state to a newly developing lower-ener gy state takes place. We attribute the evolution of this state to the parti cular spatial arrangement of the molecules within the columns in the plasti c columnar state. This causes the photoinduced formation of dimers, a proce ss that is absent in solutions and in polymer-dispersed systems of discotic materials and that has, so far, not been documented in the literature.