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Efficient Construction of Near-Infrared Absorption Donor-Acceptor Copolymers With and Without Pt(II)-Incorporation Toward Broadband Nonlinear Optical Materials.

Organic nonlinear optical (NLO) materials have attracted immense scientific interest in various fields. Broadband NLO response extending to near-infrared (NIR) region is extremely important and remain challenging. Herein, two diketopyrrolopyrrole (DPP)-based donor-acceptor (D-A) type π-conjugated copolymers with and without Pt(II)-incorporation are rationally designed and synthesized toward broadband NLO response materials. The broad intramolecular charge transfer (ICT) absorption reached to 1000 nm due to the strong D-A interaction is well demonstrated by photophysical characterizations. The NLO properties of copolymers are studied by using Z-scan technology. Attributing to their extended π-conjugated D-A systems and near-infrared ICT absorption properties, both copolymers exhibit laser-induced NLO response to nanosecond as well as picosecond laser pulses upon the wavelengths of 532 nm and 1064 nm. Interestingly, introducing Pt(II) into copolymer backbone can evidently improve NLO property or unexpectedly switch the NLO response from saturable absorption to reverse saturable absorption. Meanwhile, both copolymers are successfully employed as optical limiting materials and exhibit broadband optical limiting abilities. Therefore, we present an efficient strategy toward broadband NLO materials, which may significantly facilitate the understanding of organic molecular structure-property relationship and promote their practical application.