Synthesis and Ultrafast Broadband Optical Limiting Properties of a Two-Branched Twistacene.

A novel two-branched twistacene () has been designed and synthesized for application on ultrafast optical limiting. This twistacene exhibits excellent two photon absorption and two photon absorption-induced excited singlet state absorption, which was systematically investigated with a femtosecond Z-scan experiment, transient absorption spectrum, and two-photon excited fluorescence experiments. The admirable two photon absorption is attributed to the high degree of π electron delocalization in twistacene which is caused by introduction of two strong donors. The excited singlet state absorption cooperates with two-photon absorption to provide an excellent ultrafast optical limiting behavior with high linear transmittance, where the thresholds are 2.3-5.3 mJ/cm in the spectral region of 532-800 nm of femtosecond laser and 133 mJ/cm for picosecond pulse at 532 nm. These thresholds are lower than that of most of the optical limiters reported previously, which indicates is a promising candidate for ultrafast optical limiting.