Influence of the adsorption effect of graphene quantum dot on the photophysical properties and multiple antioxidant processes of gallic acid

[Display omitted] •Absorption spectra of GA-GQD cover UVA and UVB regions.•The fluorescence intensity of GA-GQD is close to zero.•The sequence of multiple antioxidant processes of GA is: e- → H3+ → e- → H1+.•The sequence of multiple antioxidant processes of GA-GQD is: e- → H2+ → e- → H3+.•The reactions of GA and GA-GQD with free radical ·OH are spontaneous. In this work, the influence of graphene quantum dot (GQD) adsorption effect on the multiple antioxidant processes and photophysical properties of gallic acid (GA) has been investigated by density functional theory. Simulated absorption spectra of the GA-GQD covered UVA and UVB regions, and its extremely weak fluorescence intensity means that it is more suitable for use as the sunscreen than GA. Moreover, in the S0 state, the sequence of multiple antioxidant processes of GA (GA-GQD) is: e- → H3+ → e- → H1+ (e- → H2+ → e- → H3+), and the first step of antioxidant processes of GA-GQD is more straightforward to occur than GA according to the specific thermodynamic parameters. Furthermore, the dynamic simulations of GA and GA-GQD reacted with free radical ·OH revealed that their antioxidant processes are spontaneous, verifying their outstanding antioxidant abilities.