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

Abstract

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 (λabs–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 pKa 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.

Coumarin-based benzilmonohydrazone as a new proton-sensitive fluorescencedye: synthesis and investigation of photophysical and acidochromic properties

“…Upon the addition of increased TFA, the absorption maxima shifted from 468 nm to 542 nm and a well-defined isosbestic point at 490 nm was observed. This large shift (72 nm) in absorption maxima can arise from the protonation of lactone carbonyl or hydrazone nitrogens due to increased ICT [15,26]. In our previous studies, we tested the acidochromic properties of a series of coumarin-based functional dyes bearing diethylamino at the 7-position of coumarin and a bathochromic shift in acidic medium was seen because of the obtained ICT between the diethylamino and protonated groups attached at the 3-position of coumarin.…”

“…Heterocyclic compounds bearing coumarin moiety are among the well-known chromophore groups for important chromogenic/fluorogenic sensors [12]. Coumarins that are substituted at the 7-position with a diethylamino group are especially well known for their applications in chemosensor chemistry, laser dyes, fluorescent markers for amino acids, anions/cations, organic light-emitting diodes, and sensitizers in DSSCs as chromogenic and fluorochromogenic chromophores [13][14][15][16][17].…”

Construction of 7-Diethylaminocoumarins Promoted by an Electron-Withdrawing Group

“…Fluorescent probes are used in basic biological research such as cell imaging, enzyme activity measurements, and protein and nucleic acid detection. Many synthetic strategies for coumarin have been reported, such as by the Perkin, 4) Pechmann, 5,6) Knoevenagel, 7) Morita-Baylis-Hillman, 8) and Mizoroki-Heck reactions. 9,10) However, most of these reactions involve C-C bonds, reaction under strongly acidic conditions, or the need for high temperature or metal catalysts, making knowledge of organic chemistry a requirement to synthesize a probe containing coumarin.…”

Synthesis of a Coumarin-Based PPARγ Fluorescence Probe for Competitive Binding Assay

“…The coumarin skeleton is used in various fields [ 26 , 27 , 28 ] and many synthetic strategies were reported [ 29 , 30 , 31 , 32 , 33 , 34 , 35 ], including C–C bond formation reactions that require advanced knowledge and techniques for probe synthesis. In contrast, we recently reported strategies for constructing a coumarin skeleton on a target protein (TCC probe) using small molecules (coumarin precursors) [ 36 , 37 ].…”