Porphyrin covalently functionalized MoS2 nanosheets: "Click" synthesis and tunable nonlinear absorption.

Functionalized MoS 2 nanosheets are of significant academic and commercial interest due to their use in electronic and photonic applications as transistors, electrocatalysts, electrodes, and nonlinear optical materials. However, MoS 2 nanosheets exhibit low reactivity and poor dispersibility in common solvents, which significantly hinders their functionalization with optoelectronic groups and their downstream applications. Herein, a porphyrin covalently functionalized MoS 2 nanohybrid (MoS 2 -Por) is synthesized by a mild thiol−ene "click" reaction. Optical studies demonstrate that a dispersion of the MoS 2 -Por nanohybrid in N , N -dimethylformamide (DMF) exhibits reverse saturable absorption (RSA) behavior to femtosecond pulsed laser irradiation at 800 nm, in contrast to the saturable absorption (SA) displayed by MoS 2 nanosheets. This significant switch likely stems from enhanced two-photon absorption (TPA) in the MoS 2 nanosheets, which may be ascribed to efficient charge transfer in the excited-state of the MoS 2 -Por nanohybrid. Polymethyl methacrylate (PMMA) films MoS 2 -Por/PMMA exhibit a low optical limiting threshold of 1.2 mJ cm-2 (18.3 GW cm-2), indicating great potential as an optical limiter. The MoS 2 -Por nanohybrid also exhibits stronger self-focusing than MoS 2 nanosheets towards femtosecond pulses at 800 nm due to the increased free-carries concentration arising from the improved TPA. These observations demonstrate that the MoS 2 -Por nanohybrid is an excellent candidate for optical limiting in the infrared region towards femtosecond pulses, and shed new light on the construction of covalently functionalized MoS 2 nanohybrids for tuning nonlinear optical properties and broadening application scope. • A rational strategy to synthesize the MoS 2 -Por nanohybrid. • The MoS 2 -Por nanohybrid exhibits effective intra-hybrid charge/energy transfer. • Nonlinear absorption at 800 nm is switched by MoS 2 -Por nanohybrid formation. • The MoS 2 -Por/PMMA shows a low optical limiting threshold of 1.2 mJ cm-2. [ABSTRACT FROM AUTHOR]