Tunable Nonlinear Optical Properties in Porphyrin–Cd^IIBr₂Complexes Functionalized MXenes Featuring Different Configurations

Functional materials displaying profound third-order optical nonlinearities across a wide spectral region and a broad temporal domain are required for feasible signal processing and sophisticated laser conditions. Particularly desirable are the materials with convertible nonlinear optical (NLO) activity toward both nanosecond and femtosecond pulses. Herein, for the first time, tunable NLO performance in MXene–porphyrin composite systems is realized through fine control of the configuration. Two D–A-type porphyrin–terpyridine–Cd^IIBr₂complexes with asymmetric, configuration-different structures were designed, synthesized, and subsequently incorporated with MXene (Ti₃C₂T_x) nanosheets. In these two samples, porphyrin and the Cd^IIBr₂L unit are mutually perpendicular or parallel to each other due to the benzene ring and the resulting steric hindrance. Both samples exhibit remarkably enhanced optical nonlinearity compared with their untreated samples. Notably, Ti₃C₂T_x–CdCPor (C: coplanar) possesses optimized strong NLO performance with a corresponding nonlinear absorption coefficient (β_eff) of 1.06 × 10³cm GW^–1toward the ultrafast femtosecond lasers at 800 nm, while Ti₃C₂T_x–CdOPor (O: orthogonal) exhibits strong reverse saturable absorption when it responds to nanosecond laser irradiation at 532 nm and shows no response to femtosecond lasers. These results demonstrate that the two newly developed MXene composites are very promising optical limiting (OL)candidates for practical applications across wide spectral and temporal domains and that covalently functionalizing MXene-based materials with configuration-different chromophores may be a useful and effective approach to engineering adaptable photonic devices with broad-ranging and feasible NLO activity.