Photoinduced electron transfer fluorimetric Hg(II) chemosensing based on a bodipy tetraamide derivative

A. MUÑOZ DE LA PEÑA; A. MACHUCA; R. BABIANO CABALLERO; M.J CULZONI; H.C. GOICOECHEA

Barcelona

Congreso; EUROPTRODE XI: XI Conference on optical chemical sensors and biosensors; 2012

As one of the most toxic heavy metals, mercury ions cause severe environmental and health problems even at very low concentrations. In consequence, methods for the sensitive sensing of mercury ions are of current interest. Due to its unique advantages, such as high sensitivity, low cost and fast detection, fluorescent probes have been one of the most important sensing methods for mercury ion detection. Among the fluorescent molecular probes reported the BODIPY dyes tend to be strongly UV-absorbing small molecules that emit relatively sharp fluorescence peaks with high quantum yields.In this report, we are describing the synthesis, structural determination and spectroscopic properties in the absence and presence of Hg2+ ions, of a tetramide BODIPY derivative. The synthesis was developed in a four step process based on a previously published work with some modifications.First, a solution of o-phenylenediamine and ethyl bromoacetate in acetonitrile, was refluxed for 7 hours under nitrogen. After that, the purified product was dissolved in DMF with pyridine and treated with phosphorus oxychloride in order to obtain the aromatic aldehyde derivative. The BODIPY core was generated next, by reaction with 2,4-dimethyl-3-ethylpyrrole under inert atmosphere for 5 hours, followed by the addition of DDQ, diisopropylethylamine and BF3-OEt2. Finally, the tetraamide receptor arm was synthesized by nucleophylic substitution whit 2- aminoethanol in acetonitrile. The solution was refluxed under nitrogen for 1.5 hours. The final reaction product (See Figure 1) was characterized by NMR. The tetramide substituents act as electron donors, and upon excitation of the fluorophore, an electron transfer occurs, then the fluorescence is diminished when the fluorescent group in its excited-state is reduced. In this situation, the fluorescent group is acting as an acceptor and displays very weak fluorescence, resulting from the efficient photoinduced electron transfer (PET) quenching process from the electron-donating receptor moiety to the excited BODIPY fluorophore. In the presence of Hg2+, and cation binding to the recognition tetramide moiety where the donor atom is present, the PET quenching pathway is efficiently blocked and an OFF-ON enhancement of the fluorescence is produced. The clear emission turn-on response is observed when as low as ppb level concentrations of Hg2+ are present and the reported molecular probe is able of acting as an efficient and selective chemosensor unit for environmental Hg2+ monitoring. The high selectivity of the method towards other metal ions was corroborated by an interference study and the chemosensor unit is of potential application as a fluorescence sensor intended for in situ analysis by appropriate immobilization.