Covalent functionalization of few-layer TiS2 with tetraphenylporphyrin: toward a donor–acceptor nanohybrid featuring enhanced nonlinear saturation absorption

Abstract

Covalent functionalization of two-dimensional transition-metal dichalcogenides (TMDs) enables the manipulation of optical and electronic properties in hybrid structures and enhances their versatility for various potential applications. Herein, exfoliated few-layer TiS₂ is covalently functionalized by tetraphenylporphyrin (TPP) diazonium salts for the first time. The newly synthesized TPP–TiS₂ nanohybrid is fully characterized by crystallographic, spectroscopic, microscopic, and thermal methods. Its excited-state behavior is investigated by steady-state and time-resolved photoluminescence measurements, indicating the formation of a donor–acceptor (D–A) system, in which an efficient energy transfer from the photoexcited TPP to TiS₂ layer is expected to occur. Z-scan studies show a significantly enhanced saturation absorption (SA) of the TPP–TiS₂ nanohybrid in comparison with that of pure TiS₂ at 532 nm under nanosecond (ns) pulses, though TPP exhibits typical reverse saturation absorption (RSA). The reinforced band-filling effect due to intrahybrid energy transfer may play an important role in determining the nonlinear absorption performance of TPP–TiS₂. Our results shed new light on the preparation of a TiS₂-derived nanohybrid by constructing a suitable D–A binary system, which is important in developing photonic devices such as mode-locked or Q-switched lasers.