Synthesis and two-photon properties of multi-branched fluorophores composed of ladder-type conjugated cores and functionalized diquinoxalinylamino peripheries

Two multipolar fluorophores using ladder-type oligo-(p-phenylene) units as the central π-bridges and functionalized diquinoxalinylamino moieties as the peripheral groups have been synthesized and experimentally shown to manifest strong two-photon absorption (2PA) and medium-high up-converted emission properties in the near-IR (NIR) spectral region under the irradiation of femtosecond laser pulses. Tentative analysis of the structure-2PA property revealed that in the presented structural combination, diquinoxalinylamino units are useful 2PA-enhancing subunits when properly incorporated. The π-conjugation length of the central oligo-(p-phenylene) components was also found to be one of the key parameters that relates to the magnitude of the overall molecular 2PA properties in the studied molecular system, and this structural motif provides access to highly efficient two-photon absorbers with large two-photon action cross-section values.