Study Of BODIPY And Rhodamine Fluorescent Probes For Cations

The advantages of molecular fluorescent probes for sensing can be summarized: high sensitivity of detection down to the single molecule, "on-off' switchability, subnanometer spatial resolution and submillisecond temporal resolution, observation in situ, remote sensing by using optical fibres, et al. The boron dipyrromethene (BODIPY) dyes and Rhodamine dyes have excellent photophysics and photochemistry properties such as high molar extinction coefficient, high stability against light and chemical reactions, and high fluorescence quantum yields, etc. Therefore, the studies on fluorescence molecular probes based on BODIPY dyes and Rhodamine dyes are attracting many people's attentions.pH fluorescent probes (M1-M6) based on BODIPY dyes have been designed and synthesized. M5 has the response signal from pH 5.36-3.66. The other compounds among them are the near-neutral pH fluorescent probes. M1-M6 are non-metal ion and non-anion sensitive. At the same time, it was found that the increase of number of substitutes, the increase of aliphatic chain length and the introduction of aromatic group on the nitrogen atom linked methene at site 8 of BODIPY dyes can reduce the pK_a of them. The main reason is the protonation of this nitrogen atom will lead to greater steric strain. The affinity of a proton to this nitrogen atom becomes more difficult. It is very significant for the design of this kind of pH fluorescent probes that the various substitutes on the nitrogen atom linked methene at site 8 of BODIPY dyes.The BODIPY fluorescent pH probe BDTA based on PET has been designed and synthesized. The probe has much narrow pH-sensitive windows (pH 2.00-0.65). In addition, BDTA is non-metal ion and non-anion sensitive. Therefore, BDTA is a highly sensitive and selective pH fluorescent probe.The BODIPY fluorescent compound BPb₁ based on PET has been designed and synthesized. The absorption (496 nm) and emission (505 nm) wavelengths are in visible range in acetonitrile. The fluorescence quantum yields of the lead-free and lead-bound states of BPb₁ in acetonitrile are 0.013 and 0.693, respectively. Other metal ions and anions have no obvious interference for BPb₁ to detect Pb²⁺ in acetonitrile. The fluorescence enhancement is based on the blocking of photo-induced electron transfer in BPb₁ by the selective coordination of Pb²⁺ with the receptor in the probe molecule.Cu²⁺ fluorescence enhancement probes RB2 and RG2 based on rhodamine dyes have been designed and synthesized. RB2 and RG2 exhibit Cu²⁺-only sensitive among metal ions such as Na⁺ K⁺, Mg²⁺, Ca²⁺, Ba²⁺, Mn²⁺, Cd²⁺, Cr³⁺, Co²⁺, Ni²⁺, Ag⁺, Pb²⁺, Zn²⁺, Fe³⁺, Fe²⁺, Hg²⁺ and anions such as Ac^-, Cl^-, NO₃^-, H₂PO₄^-, PO₄^3-, SO₄^2-. They have extremely high sensitivity for Cu²⁺. RB2 and RG2 would detect at least 1 nM and 0.1 nM of Cu²⁺,respectively. Upon the addition of Cu²⁺, the fluorescence enhancement factors of RB2 and RG2 are ca. 195-fold and 309-fold, respectively. RB2 and RG2 are pH-insensitive Cu²⁺ fluorescent probes, which would detect Cu²⁺ effectively in a relatively wide range of pH including the significant physiological region. After the reaction between RB2 and Cu²⁺ or between RG2 and Cu²⁺, the colour and fluorescence of solution have very obvious changes.The rhodamine fluorescent compounds RB1 and RG1 have been synthesized. RG1 has the response signal from pH 4.51-0.96. The absorbance and the fluorescent emission intensity of RG1 increase continuously when the solution became more acidic from pH 4.51 to 0.96. When pH was decreased to 0.96, the fluorescence enhancement factor of RG1 is 69-fold. In addition, RG1 is non-metal ion and non-anion sensitive. Thus, RG1 is a pH fluorescent probe which has highly sensitivity and selectivity for protons.