Synthesis and two-photon absorption properties of star-shaped chromophores derived from functionalized fluorene units

A set of small star-shaped chromophores composed of three fluorene-based congeners have been synthesized and shown experimentally to possess strong and widely dispersed two-photon absorptivities in the visible to near-IR region under the irradiation of femtosecond and nanosecond laser pulses. In addition, the number of electron-donating fluorenyl units incorporated in the final structure was closely connected to the molecular two-photon activities of these model compounds. Effective optical power attenuation and stabilization behaviors of these dye molecules in the nanosecond time domain were also investigated. The results indicate that such a structural motif could be useful in the molecular design of strong two-photon absorbing material systems for quick-responding and broadband optical suppressing-related applications, particularly for laser pulses with long durations in the near-IR region. A set of star-shaped chromophores containing functionalized fluorene units were synthesized and shown to possess ascending two-photon absorptivities with the growth of their π systems. The observed effective optical power-limiting and stabilization behaviors in the nanosecond time domain indicate that these dye molecules have potential as broadband and quick-responding optical limiters.