A set of novel multi-polar compounds composed of four fluorene-based derivatives with systematic alteration of the molecular structure was synthesized and their nonlinear optical properties in the femtosecond and nanosecond time domain were examined. Preliminary experimental results show that the two-photon activities of the model compounds are connected to structural parameters, such as the number of peripheral electron-donating groups and/or the size of the pi-domain in a dye molecule. It is also found that these model chromophores possess large nonlinear attenuation under the irradiation of laser pulses working at nanosecond regimes, indicating that these compounds may have strong two-photon-assisted excited-state absorption within the studied spectral region. Effective optical-power-limiting behaviors of the dendritic fluorophores were also demonstrated to show that such dye molecules can be potential materials for use as broadband and rapid-responsive optical limiters, especially against laser lights with longer pulses.
