Synthesis and spectroscopic properties of a novel "turn off" fluorescent probe: Thienyl-pyridine substituted BODIPY

We report the synthesis and photophysical properties of a new fluorophore compound TPy-BDP, containing thienyl-pyridine group in meso position of dipyrrin ligand. UV–Vis spectroscopy and steady state fluorimetric methods have been utilized to determine the photophysical features of this chromophore in variety of solvents. The photostability of the chromophore has been examined in solution and the dependence of spectral shifts upon solvent parameter has been studied. Also, pH sensitivity of the compound was evaluated in aqueous solutions. On binding to H⁺ ions fluorescence quenching was observed by an approximately 94% reduction in the emission intensity within the pH range of 7.6–1.0 in solution. However, no obvious fluorescence change could be observed in the basic conditions. To identify the underlying mechanism of the probe depending on pH, ultrafast pump probe experiments have been performed. The results indicate that fast electron transfer known as photoinduced electron transfer between boron-dipyrromethene scaffold to the appended group are responsible to the fluorescence quenching. Experimental results proved the capability of TPy-BDP in terms of using under strongly acidic conditions as a pH indicator.