Near-infrared II emissive diphenylaminoacridine based on the planarized intramolecular charge transfer mechanism

Small-molecule fluorophores in the second near-infrared window (NIR-II, 1,000–1,700 nm) have received widespread attention owing to their great breakthrough in deep-tissue imaging with high spatial resolution, but the strategies used to construct NIR-II fluorescent scaffolds are still very limited. Here, we report a pathway toward NIR-II wavelength-emissive fluorescent dyes, namely diphenylaminoacridine (DPA) dyes, with large Stokes shifts based on the planarized intramolecular charge transfer mechanism. DPAs exhibit tunable optical properties with the maximal absorption/emission wavelengths at 900 nm and 1,085 nm. They show high tolerance toward both photobleaching and oxidation. The in vivo gastrointestinal tract with high resolution demonstrates their significant potential in bioimaging. Overall, this work provides a promising avenue to construct NIR-II small-molecule fluorescent scaffolds for bioimaging.