Akademik Veri Yönetim Sistemi
FlatChem, cilt.56, 2026 (SCI-Expanded, Scopus)
Polyethyleneimine (PEI)-functionalized nitrogen (N)-doped graphene quantum dots (PEI N-GQDs), their Schiff base-modified imine derivatives (Schiff-PEI N-GQDs), and related metal nanoparticle (Ag, Mn, Co) nanocomposites were synthesized to investigate their broadband nonlinear optical (NLO) and optical limiting (OL) properties. Imine functionalization and metal integration significantly modulate the excited-state dynamics and charge transfer properties of GQDs. While CoNPs/PEI N-GQDs and MnNPs/PEI N-GQDs systems exhibit photoluminescence profiles similar to those of pure PEI N-GQDs, AgNPs bound to 4,6-dimethoxysalicylaldehyde-modified PEI N-GQDs exhibit pronounced fluorescence quenching due to strong intramolecular charge transfer (ICT). This mechanism has been confirmed by ultrafast transient absorption spectroscopy. The analysis of femto- and pico-second Z -scan measurements has revealed a range of distinct nonlinear absorption (NA) mechanisms, with the variation in these mechanisms occurring in accordance with the wavelength, extending from the ultraviolet to the near-infrared region (400–1200 nm). AgNPs/4,6-DIMETSAL-PEI N-GQDs exhibit superior NA behavior attributed to plasmonic field enhancement and the lowest OL thresholds at 400 nm; MnNPs/PEI N-GQDs exhibit dominant NA in the near-infrared region due to defect-state-supported multi-photon absorption processes. Density functional theory (DFT) calculations reveal increased polarizability, high dipole moment, and electronic stability in the AgNP-based Schiff base system, supporting the experimentally observed strong NA behavior. These results provide a clear structure-property-mechanism relationship for the design of GQD-based nanocomposites with wavelength-selective OL performance.