Covalent functionalization of tin disulfide with porphyrin for ultrafast optical limiting

Competitive optical limiters that can protect sensitive instruments and eyes from intense ultrafast laser irradiation across a wide spectral range are key to the expanding use of ultrafast pulsed lasers. Herein, for the first time, we report a facile and covalent diazonium approach to the functionalization of tin disulfide (SnS₂) nanosheets with organic porphyrins, in the pursuit of excellent optical limiting performance. The SnS₂-porphyrin nanohybrid (SnS₂-Por) was assembled by reacting SnS₂ nanosheets with a porphyrin diazonium salt that had been chemically activated with the reducing agent potassium iodide. In the femtosecond (fs) regime, the SnS₂-Por nanohybrid shows significantly enhanced reverse saturable absorption and effective nonlinear optical absorption coefficients, which are 2.8- to 5.8-fold higher than those of pristine SnS₂ nanosheets under identical laser irradiation; the optical limiting thresholds of the SnS₂-Por nanohybrid are 2736 μJ cm⁻² at 800 nm and 1650 μJ cm⁻² at 515 nm, which outstrip most reported fs-active NLO materials (e.g., WS₂, InSe, carbon nanodots, and graphene oxide), suggesting promising applications in ultrafast optical limiting. A dynamic energy model was proposed to demonstrate the relationship between charge transfer in the excited states of the SnS₂-Por nanohybrid and the nonlinear optical performance. This work not only offers a paradigm for facile covalent functionalization of SnS₂, but it also sheds new light on the construction of nanohybrids with excellent optical limiting performance.