Synthesis and two-photon absorption properties of ladder-type chromophores with functionalized pyrazine units fused as the end-groups

Three new multipolar chromophores based on ladder-type units (fluorene, indenofluorene, and bisindenofluorene) as the central π-bridges and with functionalized pyrazine moieties fused at the molecular terminal positions have been designed and synthesized in order to serve as a set of model compounds for the study of possible effects on the molecular two-photon absorption (2PA) properties that might be introducible by the structural arrangement. Preliminary experimental results showed that these model dye molecules display broad and intense 2PA in the near-IR region. Tentative analysis of the relationship between structure and 2PA revealed that the π-conjugation length of the central oligo-p-phenylene component is closely related to the magnitude of overall molecular 2PA and that such a structural motif provides access to highly efficient nonlinear absorbers.