Synthesis of Dimeric Pyridinium Phenolate Dyes and Investigation of their Photophysical Properties

Solvatochromic dyes have advanced the field of organic materials chemistry with their intriguing photophysical properties. They have applications as solvent polarity sensors as well as probes for studying solvent effects in supramolecular chemistry, chemical sensing, and examining biological processes. This study focuses on synthesising a range of bridged pyridinium based chromophores and investigating their photophysical behavior. This work aims to explore how solvatochromism and exciton coupling enhances the optical and electronic properties of these dyes. To do this, dimer 4,4'-((1,3-phenylenebis(methylene))bis(pyridine-1-ium-1,4-diyl))diphenolate (19), 4,4'-((1,2-phenylenebis(methylene))bis(pyridine-1-ium-1,4-diyl))diphenolate (21) and reference compound, 4-(1-benzylpyridin-1-ium-4-yl)phenolate (23) were synthesised in good yields using simple SN2 reaction. UV-vis spectroscopic analysis of these dyes was performed and compared against each other. The absorption spectrum profiles revealed that dimer 19 and 21 exhibited an enhanced negative solvatochromism compared to monomer 23. It was also observed that bichromophoric 19 and 21 exhibited intense absorption with two peaks as a result of exciton coupling. The two chromophores interact intramolecularly, resulting in the splitting and an intense absorption band. This new findings will expand the applications of these dimeric phenolate dyes in the field of material organic chemistry.