Enhanced nonlinear optical properties of MXene (Ti3C2Tx) via surface-covalent functionalization with porphyrin

The surface terminations (=O, -OH, and -F) play a key role in determining the physical and chemical properties of MXenes, which have been demonstrated with significant potential in field-effect transistors, humidity sensors, energy storage, and photocatalysis, etc. It is therefore crucial to modify these active functional groups on the surface of MXenes in order to optimize the applicability of these materials. In this study, we introduce a covalent modification strategy to successfully construct a porphyrin-functionalized Ti₃C₂T_x organic-inorganic nanohybrid (TPP-Ti₃C₂T_x) by covalently attaching porphyrin molecules to the surface groups on Ti₃C₂T_x nanosheets for the first time. As revealed by steady-state fluorescence spectra, transient fluorescence spectra, and DFT calculations, the robust covalent bonds between TPP and Ti₃C₂T_x can effectively promote the photon-induced electron and/or energy transfer within the TPP-Ti₃C₂T_x nanohybrid. The investigation on the nonlinear optical (NLO) properties of TPP-Ti₃C₂T_x nanohybrid as well as its precursors, reveals that the TPP-Ti₃C₂T_x nanohybrid exhibits the highest nonlinear absorption coefficient and the lowest optical limiting threshold among the tested samples at both 532 and 1064 nm, indicating its great potential as a broadband optical limiter for visible and near-infrared wavelengths. This work not only demonstrates the significant promise of covalently-linked TPP-Ti₃C₂T_x nanohybrid in optical limiting applications but also provides a paradigm for engineering high-performance NLO MXenes-based materials through the covalent modification strategy.