Exploring Charge Transfer Mechanisms in Schiff Base-Modified N-Doped GQDs: Insights from DFT and Pump-Probe Spectroscopy for Bioimaging Applications

In recent developments, graphene quantum dots (GQDs) have emerged as valuable tools for imaging and biosensing. Various modifications on the GQDs with any desired functionality and attachment of organic molecules and/or nanostructures allow tuning their photophysical properties as well as charge transfer dynamics for bioimaging applications. This study focuses on synthesizing and characterizing of polyethyleneimine-functionalized nitrogen-doped GQDs (NC1), Schiff base- functionalized nitrogen-doped GQDs (NC2), and silver nanocomposites of these Schiff base-functionalized nitrogen-doped GQDs (NC3). We explore their absorption and emission properties to understand their interactions in the ground state. Furthermore, ultrafast transient absorption spectroscopy measurements reveal that the presence of NC3 shortens the excited state lifetime of NC1 due to charge transfer, resulting in reduced fluorescence intensity. Both experimental and DFT results suggest the potential of NC3 for bioimaging and sensing applications, making them promising candidates for phototheranostic purposes.