Large ultrafast nonlinear optical response and excellent optical limiting behaviour in pyrene-conjugated zinc(II) phthalocyanines at a near-infrared wavelength

The design and synthesis with full structural utilization of a new type of nonlinear photonic material, Zinc(II) phthalocyanine macrocycle (Pc-pyrene), bearing binary oriented (up/down) pyrene units is reported. The novel pyrene-based macrocycle has been successfully obtained in high yield upon coupling multiple azido pyrene derivatives on a previously fabri-cated alkynyl-substituted macrocyclic platform (Pc1) via multiple tandem Cu(I)-catalysed azide-alkyne cycloaddition (CuAAC) reactions. The ultrafast nonlinear optical characteristics of both Pc1 and Pc-pyrene have been investigated in solution using a near-infrared femtosecond pulsed laser. The femtosecond Z-scan results reveal a low optical limiting threshold and a good set of figures of merit that make these macrocycles feasible for optical limiting as well as switching applications. In a major breakthrough, ultrafast laser-induced deformations in Pc-pyrene-embedded PMMA films results in a very large enhancement of the three-photon absorption coefficient at 800 nm by up to ~10⁵ times that of Pc solutions. Furthermore, the deformed Pc-pyrene PMMA films having the advantage of flexibility and possess an excellent optical limiting threshold (0.0018 J/cm²), much lower than various previously reported values, which enables them to be one of the best optical limiters.