Synthesis of some 8-anilino bodipy dyes and their applications in chromofluorogenic nitrite ion detection in water

In this thesis study, two 8-(4-anilino) BODIPY derivatives (NP-1 and NP-2) were synthesized, and their potential for nitrite ion detection was investigated. The compounds were prepared by condensing 4-nitrobenzaldehyde and 2,4-dimethylpyrrole in an acidic medium to obtain the corresponding dipyrromethane derivatives. Subsequently, these derivatives were oxidized using DDQ to produce dipyrromethene intermediates. These intermediates were then treated with boron trifluoride etherate in a basic medium to yield the precursor compounds, 8-(4-nitrophenyl) BODIPY derivatives. Finally, these compounds were reduced with iron (iron powder) in an acidic medium to successfully synthesize the target 8-(4-anilino) BODIPY derivatives, NP-1 and NP-2. UV-vis spectroscopy revealed that NP-1 exhibited a significant red shift (6 nm) in response to pH changes due to the electronic delocalization effects of hydrogen substitution at the 5- and 7-positions. In contrast, NP-2, with methyl substituents at these positions, displayed a more limited red shift (3 nm) due to steric hindrance. Moreover, when the effect of pH on the fluorescence emissions of the probes was investigated, it was found that under increasingly acidic conditions, the emission recovery of NP-2 was approximately 85 times higher compared to that of NP-1. Fluorescence emission analysis showed that NP-2 exhibited high initial fluorescence emission, which diminished sharply in the presence of nitrite ions. NP-1, on the other hand, demonstrated low emission, enabling detection through colorimetric changes. The findings suggest that NP-1 is a suitable candidate for colorimetric sensing, while NP-2 is better suited as a fluorescence probe for nitrite detection. This study is expected to inspire the design of new probes for various analytes.