Abstract:

TPA properties of carbozole-core and triphenylamine-core multi-branched 1,3,4-oxadiazole derivatives were measured with nonlinear transmission method. Single-photon excited fluorescence and two-photon excited fluorescence of chromophores were experimentally studied. When pumped with 800 nm laser irradiation, 9-ethyl-3,6-bis(2-{4-[5-(4-tert-butyl-phenyl)-[1,3,4]oxadiazol-2-yl]-phenyl}-vinyl)-carbazole(3) and tris[4-(2-{4-[5-(4-tert-butyl-phenyl)-[1,3,4]oxadiazol-2-yl]-phenyl}-vinyl)-phenyl]-amine(4) show strong two-photon excited blue and yellow green fluorescence at 485 nm and 547 nm respectively. These multibranched chromophores showed a large TPA cross-section(values of >10⁴ GM can be achieved) and strong optical power limiting properties. The cooperative enhancement of TPA in these multi-branched structures was observed. This enhancement is partly attributed to the electronic coupling between the branches. The electronic push-pull structures in the repeated unit and their cooperative effect increase the TPA properties of multi-branched molecules.

Key words: Oxadiazole derivative, Two-photon absorption cross-section, Two-photon excited fluorescence, Optical power limiting