Proton Sensitive Functional Organic Fluorescent Dyes Based on Coumarin-imidazo[1,2-a]pyrimidine; Syntheses, Photophysical Properties, and Investigation of Protonation Ability

摘要

A novel series of 2-coumarin-3-yl-imidazo[1,2-a]pyrimidines have been synthesized with functionalized coumarin and pyrimidine units of the different architecture to give various fluorescent compounds. A new additional series bearing unsubstituted coumarin and 7-dialkylaminocoumarin as fluorophore were obtained by palladium-catalyzed cross-coupling reactions, through coupling of 6-bromo-2-coumarin-3-yl-imidazopyrimidine derivatives with various arylboronic acids. In the all reaction step, microwave irradiation (MWI) method was used and compared with the conventional method (CM). Photophysical properties of synthesized compounds were studied by a combination of UV/Vis and fluorescence spectroscopy in various solvents having different polarities. The protonation abilities of all compounds were investigated by titration with trifluoroacetic acid (TFA) in dichloromethane. In both series, the compounds bearing 7-dialkylaminocoumarin are fluorescently active even in daylight and showed maximum absorption wavelengths (λ_(abs-max)) in the visible region in all solvents used. In addition, they showed drastic color and emission change in acidic environment. Moreover, for the investigation of protonation ability of three selected compounds bearing 7-dialkylaminocoumarin have been studied using a buffer solution with various pH and determinated their pK_a values. The compound bearing morpholine has the potential to use as colorimetric and luminescence pH sensor. The thermal properties of all the synthesized compounds were also evaluated with TGA to test their usability as optic dyes.