Effect of Amino-Functionalized Graphene Quantum Dots on Unoccupied Electronic States of Donor–Acceptor Thiophene-Based Copolymer: A Core Level Spectroscopy Investigation

In this work, the effects of electronic interactions between amino-functionalized graphene quantum dots (AF-GQDs) and the unoccupied electronic states of the donor–acceptor thiophene-based copolymer poly[2,7-(9,9-dioctylfluorene)-alt-4,7-bis(thiophen-2-yl)benzo-2,1,3-thiadiazole] (PFO–DBT) were investigated using X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure spectroscopy (NEXAFS), and resonant Auger spectroscopy (RAS). XPS analysis revealed noncovalent interactions between PFO–DBT and AF-GQDs, which induced changes in the molecular configuration of the copolymer. S K-edge NEXAFS spectra indicated that thiophene units preferentially adopt an edge-on orientation, while benzothiadiazole units lie on-plane, a configuration modulated by interactions with AF-GQDs that reduce the planarity of the polymer backbone. The degree of electronic delocalization was probed via sulfur KL₂,₃L₂,₃ RAS, revealing strong localization of electrons excited to the π*(S–N) states of benzothiadiazole, and enhanced delocalization for electrons excited to the π*(S–C) states of thiophene. These effects are directly correlated with conformational changes, particularly increased torsional disorder. This study offers fundamental insights into how functionalized carbon nanostructures influence the electronic structure and molecular conformation of donor–acceptor copolymers, providing valuable guidelines for the designing next-generation optoelectronic materials with tailored charge transport and excitonic properties.