Plasmonic Enhanced Nonlinear Absorption of Tris(2-aminoethyl)amine (TREN) Functional Ag, Pt, and Pd Nanoparticle-GQDs Complexes and Their Evaluation as Potential Bioimaging Applications

Tris (2-aminoethyl)amine (TREN) functionalized N-doped graphene quantum dots (N-GQDs) and their Ag, Pd, and Pt nanocomposites were synthesized via a green one-step method and comprehensively characterized using FT-IR, UV-vis, TEM, and EDX. Spectroscopic analysis revealed π-π* transitions of C═C bonds (245-250 nm) and <i>n</i>-π* transitions of C═O and C═N bonds (334-350 nm), elucidating the materials' optical properties. Photoluminescence studies revealed excitation wavelength-dependent emissions, indicating the presence of edge defect levels. Femtosecond transient absorption spectroscopy revealed a shortened excited-state lifetime upon incorporation of a metal atom into TREN-GQDs. Nonlinear absorption was explored by using the open-aperture Z-scan method, revealing enhanced performance upon incorporation of plasmonic nanoparticles. Ag-incorporated samples exhibited the highest NLA response due to plasmon-enhanced two-photon absorption. Notably, Pt-incorporated N-GQDs showed improved NLA and good biocompatibility with the intracellular fluorescence response, positioning them as promising candidates for bioimaging applications. Density functional theory (DFT) calculations, including gas-phase optimizations and aqueous simulations, confirmed alignment with experimental results, highlighting the enhanced stability and reactivity of nanocomposites. These findings highlight the potential of these materials in various applications, such as optical limiting, imaging, photovoltaics, and sensing applications.