A Novel o-vanillin-based Triimine-Schiff Base as an Effective Blue-green Emissive Fluorophore in Solution

Ortho-hydroxy symmetric diimine-Schiff base 6,6'-(((2-nitro-1,4-phenylene)bis(azanylylidene))bis(methanylylidene))bis(2-methoxyphenol) (D₁) was prepared by using 2-nitro-para-phenylenediamine and ortho-vanillin. Nitro group of diimine has been completely reduced into aromatic amine, and then reacted with 4-chlorobenzaldehyde to obtain a new asymmetric triimine-Schiff base 6,6'-(((2-((4-chlorobenzylidene)amino)-1,4-phenylene)bis(azanylylidene)) bis(methanylylidene))bis(2-methoxyphenol) (T₁). Spectral structure analyses reveal that this molecule exists in OH tautomeric form in the solid state and solution, attributed to a strong intramolecular hydrogen bond interaction between the phenolic protons and nitrogen atoms. The effects of solvent polarity and different excitation wavelengths (λ_exc = 365-640 nm) on the excited state intramolecular proton transfer (ESIPT) process have been examined by absorption and emission spectra. After excitation at 365 and 385 nm, T₁ shows bright blue-green, bluish-green and greenish-blue light, and emission band is centered at λ_max = 473-481 nm and 472-493 nm in these solutions, causing noticeable changes in the intensity. The fluorescence spectra display different λ_em at the excitation wavelengths of 470 and 530 nm, whereas T₁ is non-emissive in all solutions. The optical properties of triimine have been investigated graphically by Tauc and Absorbance Spectrum Fitting (ASF) methods using UV-Vis absorbance spectroscopy. Some physicochemical and pharmacokinetic parameters have been determined through in silico SwissADME technique.