Design, synthesis, and spectroscopic profiling of novel coumarin dyes: Investigating solvent sensitivity and photophysical properties

Coumarin dyes are highly versatile and widely employed as fluorescent chemosensors in a variety of fields, including molecular imaging, bioorganic chemistry, analytical chemistry, materials chemistry, biology, and medical science. Thanks to their outstanding photostability and high quantum yield, they represent an ideal choice for developing sensitive and selective sensing platforms. In this study, we successfully designed and synthesized four new dyes based on the coumarin dye molecular skeleton, investigating their solvent sensitivity and spectroscopic properties. Our novel coumarin dyes were synthesized by a straightforward approach, reacting coumarin-3-carboxylic acid succinimidyl ester derivatives with corresponding amines in 1,4-dioxane as a solvent. We carefully monitored the completion of the reactions using thin -layer chromatography (TLC) and characterized these dyes using spectral and elemental analyses. We further investigated the UV, fluorescence, timecorrelated single photon counting (TCSPC) technique and time -resolved spectroscopy (TRES) of these dyes in different solvents and on polymer film poly(methyl methacrylate) (PMMA). The quantum yield of the synthesized dyes was determined, with values observed to range between 0.55 and 0.94. Most of the dye-solvent and dye-polymer combinations exhibited single exponential decay, with lifetimes ranging from 2.3 to 3 ns. Minor deviations from single exponential behavior were observed for most of the dyes in toluene, while significant deviations were observed for coumarin dyes with piperazine moiety. We have provided a rationalization of these results in terms of the chemical functionalities of the various dyes. Furthermore, we investigated the effect of interactions between 7-methoxy-2-oxo-N-(2-(piperazin-1-yl)ethyl)-2H-chromene-3-carboxamide and silica nanoparticles (Ludox) on the spectroscopic properties of these dyes, with charge transfer being one possible mechanism contributing to the behavior of the dyes. Additionally, we explored the effect of trifluoroacetic acid (TFA) on the dyes' emission intensity and fluorescence decay. Based on our UV and fluorescence measurements of the dyes in different solvents, we have concluded that these dyes can create excellent donor-acceptor pairs for our upcoming fluorescence resonance energy transfer (FRET) experiments.