Synthesis and spectroscopic investigation of cationic donor‐(π‐bridge)‐acceptor dye, 4‐[ N ‐(5,6,7,8‐tetrahydroisoquinolinium‐5‐ylidene)methyl]‐ N , N ‐dialkylaniline iodide

Abstract

The synthesis and fundamental spectroscopic properties of eight hemicyanine (HC) dyes are presented. The dyes were prepared by the condensation of N-methyl-5,6,7,8-tetrahydroisoquinolinium iodide with p-(N,N-dialkylamino)benzaldehydes. The compounds were characterised by nuclear magnetic resonance spectroscopy and their purity was checked with the use of thin-layer chromatography. The spectroscopic properties of the dyes were determined in three organic solvents. The electronic absorption spectra of the dyes demonstrate moderate sensitivity to the nature of the substituent present in the aromatic ring and low solvent polarity dependence. In contrast to this, the positions of fluorescence bands are affected by the structure of an electron donor and solvent polarity. The 4-[N-(5,6,7,8-tetrahydroisoquinolinium-5-ylidene)methyl]-N,N-dialkylaniline iodides were applied as fluorescent probes for the monitoring of the progress of free radical polymerisation. The study on the changes in the fluorescence intensity and spectroscopic shifts of the dyes was carried out during thermally initiated polymeriszation of methyl methacrylate. The purpose of these studies was to find a relationship between the changes in the shape and intensity of probe fluorescence and the degree of monomer conversion into polymer.