A near-neutral pH near-infrared (NIR) fluorescent probe utilizing a fluorophore-spacer- receptor molecular framework that can modulate the fluorescence emission intensity through a fast photoinduced electron-transfer process was developed. Our strategy was to choose tricarbocyanine (Cy), a NIR fluorescent dye with high extinction coefficients, as a fluorophore, and 4'-(aminomethylphenyl)-2,2':6',2''-terpyridine (Tpy) as a receptor. The pH titration indicated that Tpy-Cy can monitor the minor physiological pH fluctuations with a pK(a) of approximately 7.10 near physiological pH, which is valuable for intracellular pH researches. The probe responds linearly and rapidly to minor pH fluctuations within the range of 6.70-7.90 and exhibits strong dependence on pH changes. As expected, the real-time imaging of cellular pH and the detection of pH in situ was achieved successfully in living HepG2 and HL-7702 cells by this probe. It is shown that the probe effectively avoids the influence of autofluorescence and native cellular species in biological systems and meanwhile exhibits high sensitivity, good photostability, and excellent cell membrane permeability.

The first near-infrared fluorescent probe was developed toward Cu(2+). Based on the photo-induced electron transfer (PET) mechanism, the probe exhibited weak fluorescence. Upon the addition of Cu(2+), it fluoresced strongly. The probe offered this unique capability, and was successfully applied to living cells, tissues and in vivo to visualize Cu(2+).

A new nonredox fluorescent probe to realize the imaging of hydroxyl radicals (*OH) in living cells was designed and synthesized. The structure comprised the fluorescent dye boron dipyrromethene (BDP) and a 2,2,6,6-tetramethyl-1-piperidinoxyl (TEMPO) unit. This probe could rapidly respond to *OH with a detection limit of 18 pM, and it possessed superior photostability and pH insensitivity. Other reactive oxygen species (ROS) and relevant intracellular components did not interfere. In particular, the important problem of ONOO(-) interference was efficiently avoided. An MTT assay proved that the probe was not very cytotoxic. The probe could penetrate into intact cell membranes to selectively detect intracellular *OH without causing cellular damage in living mice macrophages, normal human liver cells. and human hepatoma cells. These advantageous characteristics make the fluorescent probe potentially useful as a new candidate to detect *OH in broad biosystems.

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The title compound (I) detects Cu2+ with high sensitivity and selectivity and its fluorescence increases ten‐fold during the reversible binding process.