Amphiphilic Nanographene with Aggregation-Induced Type-I Photodynamic Properties

Fluorescent graphene quantum dots (GQDs) have emerged as promising phototheranostic agents. However, most of the reported GQDs only show Type-II photodynamic (PD) effect, which is not effective in the hypoxic tumor interior. Moreover, little is known yet about the mechanism of the PD and photothermal (PT) effects of GQDs, whose precise chemical structures are typically unknown. Here, we utilize an amphiphilic nanographene, namely dibenzo[ hi , st ]ovalene with tetra(ethylene glycol) chains (DBOV-OTEG), as an atomically precise GQD, and investigate its PD and PT properties both as individual molecules and aggregates. While red-emissive DBOV-OTEG showed the Type-II PD effect when dissolved in tetrahydrofuran, without displaying the Type-I PD effect, its aggregation in water led to the activation of the Type-I PD effect, along with suppressed fluorescence, enhanced PT effect, and deactivation of the Type-II PD effect. Theoretical calculations and ultrafast transient absorption spectroscopy revealed that intermolecular charge-transfer (CT) states are populated in aggregates, accounting for this remarkable aggregation-induced modulation of the photophysical properties. Moreover, DBOV-OTEG was taken up by live cells and accumulated in lysosomes, enabling the subcellular organelle-targeting photo-elimination of cancer cells. Such amphiphilic nanographenes with the aggregation-induced Type-I PD properties can potentially enable environment-dependent electron transfer, which might be useful for locally promoting different photoredox reactions.