Synthesis, spectroscopic characterization and photophysics of a novel environmentally sensitive dye 3-naphthyl-1-phenyl-5-(4-carboxyphenyl)-2-pyrazoline

Synthesis and photophysical properties of a novel pyrazoline - containing fluorophore, 3-naphthyl-1-phenyl-5-(4-carboxyphenyl)-2-pyrazoline (NPCP) A, and its proline derivative (NPCP-P) B are presented in this work. The highlight of this fluorescent dye is that, it can be prepared from available starting material via two synthetic steps, easily converted to the corresponding amide derivative by in situ nucleophilic acyl substitution of the corresponding acid chloride, and its purification by simple chromatographic techniques. The structures of the new compounds were verified using various spectroscopic tools. Furthermore, photophysical properties of the new fluorophores were studied and interesting solvatochromic behaviour was observed. Due to the presence of proton acceptor linked to the fluorophore, NPCP displays pH-sensitive absorption and fluorescence emission. The interaction of NPCP and NPCP-P with various micelles has been studied by steady state fluorescence. All results reflect the importance of the medium effect on the analytical application of NPCP as a potential fluorescent label for derivatization of analytes having amine (-NH₂) group. Theoretical calculations were performed for both compounds using time dependent density functional theory (TD-DFT) at B3LYP/6-31G(d, p) level. The calculations indicate that the exited state dipole moments are larger than those of the ground state in line with the experimental findings.