Mild acidic-enhanced mitochondrial-targeting by a neutral thiophene based terpyridine molecule with large two-photon action cross-section

Compared to cationic molecules, neutral mitochondrial targeting probes rarely exist. Herein, neutral thiophene based terpyridine (-β, -γ) organic probes have been synthesized and systematically characterized. The results from photophysical property investigations indicate that all the compounds possess considerable two-photon activities, and one of these probes possesses the largest two-photon action cross section (Φδmax) value (OT1, 850 nm, ∼370 GM) compared with previously reported mitochondrial imaging agents. Importantly, such probe in mild acidic external environment can trigger significant protonation, and subsequently enhance mitochondrial-labeling using around 10−8 M range concentrations for days. This result may offer a novel strategy to design the probes for mitochondria.