Design And Synthesis Of New Cation-Sensitive Fluorescent Probes Based On Porphyrins And Rhodamin Spirolactam

Molecular recognition is the main field of Supramolecular chemistry, first advanced by organic chemist and biologic chemist when they investigate chemical problem. It in nature is the process that the host molecular integrates with guest molecular and produces a special function at this process. We need special tool to detect the process of molecular recognition and the changes of microcosmic environment during the sensing event. Fluorescent probes can transfer molecular recognition events into fluorescence signals and then make a bridge between man and molecule. The advantages of molecular fluorescence 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. Fluorescence molecular is special designed and selective recognition events, then transfer molecular recognition events into fluorescence signals and at last make a bridge between man and molecule. This is fluorescence probe molecular.Porphyrins are attractive candidates of fluorescent probes owing to their good photophysical properties with strong fluorescence, large Stokes shifts and relatively long excitation (>400 nm) and emission (>600 nm) wavelengths that minimize the effects of the background fluorescence. Tetraphenylporphine shows high selectivity toward to Hg²⁺. It is a problem to switch in the recognition preference in Tetraphenylporphine throng modification. At last, we synthesize 5-(2, 3, 4-trihydroxylphenyl)-10, 15, 20-triphenylporphyrin as a new fluorescent probe for Cu²⁺. Other ions especial Hg²⁺ do not interfere with Cu²⁺-induced fluorescence change. The probe exhibits a linear fluorescent response towards Cu²⁺ in the concentration range of 1.9×10^-6–5×10^-5mol/L. At the same time, we design and synthesize N-methyltetraphenylporphyrin throng modify a methyl in the pyrrolic nitrogens, and successfully switch in the recognition preference. The fluorescence emission intensity of N-methyltetraphenylporphyrin is remarkably enhanced upon the addition of Zn²⁺ which is attributed to the formation of 1:1 stoichiometry complexation for compound 1 with Zn²⁺. It shows a linear response toward Zn²⁺ in the concentration range of 5.0×10^-7–1.0×10^-5 mol/L.Designing chemosensors based on rhodamine spirolactams has several advantages: they display not only great absorbance and fluorescence intensity enhancement toward some specific metal ions, but also a strong color development against the colorless blank during the sensing event. So, this is an ideal modal for the design of light"off-on"switch sensors. Recently an excellent job of opening the spiro ring of rhodamine spirlactam-based chemodosimeter was published. We noticed that N(py) and N (imine) is mainly coordinate to Hg²⁺ ion, however, one carboxyl and the other nitrate anion very weakly coordinate to the Hg²⁺ ion. And another splendid job of opening the spiro ring of rhodamine was reported via Cu²⁺ ion binding at the nitrate anion, carboxyl. Bearing this in mind, we envisaged that, by altering a bond, it may be possible to carry out a rhodamine spirolactam based fluorescent probe highly selective for Cu²⁺ ions by color/fluorescence changes. On the basis of above consideration, we design a new rhodamine-based fluorescent probe 3, which displays a selective and sensitive Cu²⁺ -amplified fluorescence in neutral buffered media. Cu²⁺ displayed a 66-fold enhancement at 50μM. It shows a linear response toward Cu²⁺ in the concentration range of 2.0×10^-6–1.0×10^-5 mol/L.