Aggregation-induced emission of matrix-free graphene quantum dots via selective edge functionalization of rotor molecules

Graphene quantum dots (GQDs) are nanosized graphene derivatives with unique photoluminescence (PL) prop-erties that have advantages in optoelectronic applications due to their stable blue light emission. However, ag-gregation-caused quenching (ACQ) of GQDs limits the practical applications on light-emitting diodes. Here, we suppress the ACQ phenomena of GQDs by reducing the size and converting GQDs into aggregation-induced emission (AIE)-active materials. As the size of GQDs is reduced from 5 to 1 nm, their solid-state PL quantum yields (PLQYs) are improved from 0.5 to 2.5%, preventing ACQ. Two different rotor molecules, benzylamine (BA) and 4,4 & PRIME;-(1,2-diphenylethene-1,2-diyl)diphenol (TPE-DOH), are selectively functionalized by substituting carboxylic acid and carbonyl functional groups. All functionalized GQDs show AIE behaviors with significantly enhanced solid-state PLQYs, up to 16.8%. Afterglow measurements and theoretical calculations reveal that se-lective functionalization hinders inter-and intramolecular charge transfer, which enhances the fluorescence rate of GQDs and corresponding PLQY.