A novel turn-on fluorescent 8-amino BODIPY-based probe carrying a thiourea unit as the mercury ion recognition unit has been developed. Due to the cascade reaction processes, consecutive color changes reflecting the electronic absorption and emission responses were observed upon addition of increased concentrations of mercury(II) ions. The likely sensing mechanism was proposed as mercury ion-promoted cyclization and subsequent hydrolysis. The probe displayed a selective response to mercury ions over other metal ions. Additionally, experiments with living Human Hepatoma SMMC-7721 cells to visualize intracellular mercury ions in biological systems were carried out with the probe.

The co-existence and similar properties of amino acids make the detection of individual amino acids challenging. Herein we discovered that probe 1 may act as a smart example to classify and differentiate basic amino acids (Arg/Lys/His), thiol-containing amino acids (Cys/HCy), and GSH through different sensing mechanisms in selected environments.

A new selective fluorescent and colorimetric chemosensor for the detection of GSH was developed. The discrimination of GSH from Cys and Hcy is achieved through two emission channel detection. The detection limit of probe 1 for GSH reached 10 nM (3 ppb). The excellent sensitivity and selectivity of probe 1 allow the selective detection of GSH over Cys and Hcy, which can be visualized colorimetrically and/or fluorescently. The sensitive detection of GSH allowed for convenient measurement of the GSH content in human plasma. The presence of GSH in cells was demonstrated through cell imaging.

A highly selective and sensitive turn-on red fluorescent 1-amino BODIPY-based probe (where BODIPY denotes indole-based boron-dipyrromethene) with high off-to-on contrast ratio has been developed. The probe displayed selective response to thiophenols over aliphatic thiols. Probe 1 is promising for the quantitative detection of thiophenol with a linear response from 6 × 10–6 M to 1 × 10–4 M, and the detection limit for thiophenol (PhSH) reaches 4 × 10–6 M measured in acetonitrile/PBS buffer. The detection limit could be improved to 37 nM (detection limit to 4 ppb) in water when 1% Tween 20 was used to assist the dissolvation of probe 1 in water. Probe 1 is also a useful fluorescent probe for detecting thiophenols in living cells in red emission, which may greatly improve the detectable sensitivity.

Mono- and bis-dialkylaminophenylbuta-1,3-dienyl boron-dipyrromethenes (BODIPYs) 1–12 were synthesized in 36%–42% yields by a Knoevenagel-type condensation. The absorption and emission maxima (λabs = 614–739 nm; λem = 655–776 nm in CHCl3) of 1–12 covered from the visible to the near-infrared region. Probe 1 was ratiometric Vis pH probes. Such probe was almost non-fluorescent. Upon the protonation of the tertiary amine function of 1, the strong fluorescence (Φf = 0.97) was released and the florescence intensity was dramatically increased by one thousand folds. The sharp isosbestic points were discovered at 590 nm, which was a ratiometric pH probe.Mono- and bis-dialkylaminophenylbuta-1,3-dienyl BODIPYs 1–12 (λabs = 614–739 nm; λem = 655–776 nm in CHCl3) were synthesized by a Knoevenagel-type condensation. Upon the protonation of the tertiary amine function of 1 as a pH probe, the strong fluorescence (Φf = 0.97) was released and the florescence intensity was dramatically increased by one thousand folds.

A BODIPY-based turn-on NIR fluorescent probe containing a partially exposed aldehyde group at the meso position for the detection of homocysteine over cysteine was developed. Such a probe is potentially useful for the discrimination of Hcy from Cys.

Mono- and di-AcO substituted BODIPYs (1 and 2) were synthesized from TM-BDP. The structures of 1 and 2 were supported by single crystal X-ray analysis. Both 1 and 2 possess a large absorption coefficient, high fluorescence quantum yield, and high light stability. Compound 2 has much improved water solubility which is highly desirable for biological applications. Theoretical calculation supports our observations in X-ray analysis, absorption, and cyclic voltammetry.

A novel 3,4,4a-trihydroxanthene-fused pyrrole 2 was synthesized by the reaction of 2,3,4,4a-tetrahydro-1H-xanthen-1-one with 3-phenyl-2H-azirine in the presence of LDA. Utilizing this pyrrole 2, a NIR BODIPY 1 (λabs = 732 nm, λem = 747 nm) has been prepared. The new BODIPY 1 was stable, non-cytotoxic, and suited to labeling living cells for imaging assay in the NIR region.

A selective and sensitive turn-on fluorescent NIR probe for cysteine has been developed. Cleavage of 2,4-dinitrobenzenesulfonyl (DNBS) with thiols switches the weakly fluorescent aza-BODIPY dye (λem = 734 nm, Φf = 0.03) to a strongly fluorescent species in the NIR region (λem = 755 nm, Φf = 0.14).

NIR diaryl aza-borondipyrromethene dyes (C-aza-BODIPY) and dialkynyl aza-borondipyrromethene dyes (E-aza-BODIPY) were synthesized from difluoro aza-borondipyrromethene dyes (F-aza-BODIPY) in 45–83% yields. By X-ray analysis the N–B distances (1.603 and 1.606 Å) in C-aza-BODIPY were found to be longer than the corresponding bond of C-BODIPY by 0.02–0.04 Å. C-aza-BODIPYs display remarkable blue shifts and low fluorescence quantum yields, and E-aza-BODIPYs have moderate fluorescence quantum yields (0.16–0.29). C- and E-aza-BODIPYs display good stability in weak acidic and basic conditions. E-aza-BODIPY was dialytic and suitable to staining of living cells.

A selective and sensitive turn-on fluorescent NIR probe for cysteine has been developed. Cleavage of 2,4-dinitrobenzenesulfonyl (DNBS) with thiols switches the weakly fluorescent aza-BODIPY dye (λem = 734 nm, Φf = 0.03) to a strongly fluorescent species in the NIR region (λem = 755 nm, Φf = 0.14).

A new selective fluorescent and colorimetric chemosensor for the detection of GSH was developed. The discrimination of GSH from Cys and Hcy is achieved through two emission channel detection. The detection limit of probe 1 for GSH reached 10 nM (3 ppb). The excellent sensitivity and selectivity of probe 1 allow the selective detection of GSH over Cys and Hcy, which can be visualized colorimetrically and/or fluorescently. The sensitive detection of GSH allowed for convenient measurement of the GSH content in human plasma. The presence of GSH in cells was demonstrated through cell imaging.

The co-existence and similar properties of amino acids make the detection of individual amino acids challenging. Herein we discovered that probe 1 may act as a smart example to classify and differentiate basic amino acids (Arg/Lys/His), thiol-containing amino acids (Cys/HCy), and GSH through different sensing mechanisms in selected environments.

A novel 3,4,4a-trihydroxanthene-fused pyrrole 2 was synthesized by the reaction of 2,3,4,4a-tetrahydro-1H-xanthen-1-one with 3-phenyl-2H-azirine in the presence of LDA. Utilizing this pyrrole 2, a NIR BODIPY 1 (λabs = 732 nm, λem = 747 nm) has been prepared. The new BODIPY 1 was stable, non-cytotoxic, and suited to labeling living cells for imaging assay in the NIR region.