Porphyrin covalently functionalized MoS2 nanosheets: “Click” synthesis and tunable nonlinear absorption

Abstract

Functionalized MoS2 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, MoS2 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 MoS2 nanohybrid (MoS2-Por) is synthesized by a mild thiol−ene “click” reaction. Optical studies demonstrate that a dispersion of the MoS2-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 MoS2 nanosheets. This significant switch likely stems from enhanced two-photon absorption (TPA) in the MoS2 nanosheets, which may be ascribed to efficient charge transfer in the excited-state of the MoS2-Por nanohybrid. Polymethyl methacrylate (PMMA) films MoS2-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 MoS2-Por nanohybrid also exhibits stronger self-focusing than MoS2 nanosheets towards femtosecond pulses at 800 nm due to the increased free-carries concentration arising from the improved TPA. These observations demonstrate that the MoS2-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 MoS2 nanohybrids for tuning nonlinear optical properties and broadening application scope.