Synthesis and Photophysical Properties of Fluorescent 6-Aryl-D-π-A Coumarin Derivatives

Abstract

A series of 6-aryl coumarin dyes were synthesized in satisfactory yields by Pd-catalyzed Suzuki cross-coupling reactions with a panel of boronic acids and coumarin bromides. Photophysical studies highlighted a large Stoke shift and interesting fluorescence quantum yield for these compounds. Optical properties were also investigated with the aid of quantum chemical calculations. The treatment of selected coumarin dyes with increasing amounts of trifluoroacetic acid showed that their fluorescence can be strongly influenced by pH (fluorescence quenching at high acid concentrations), while the addition of Fe 3+ and Al 3+ metal ions allowed to highlight dichotomous behavior with the corresponding reduction in fluorescence with the increase of [Fe 3+ ] or [Al 3+ ]. Finally, biological assays and fluorescence microscopy imaging investigations indicated that these compounds can be used as potential biomarkers in living and fixed cells.

Efficient Synthesis of Fluorescent Coumarins and Phosphorous-Containing Coumarin-Type Heterocycles via Palladium Catalyzed Cross-Coupling Reactions

“…The synthesis of compounds 9a,c,d via the Suzuki reaction was previously reported by two different research collectives [ 23 , 24 ]; however, different catalytic systems were used. The obtained yields for these compounds were lower under longer reaction times.…”

“…The obtained yields for these compounds were lower under longer reaction times. For example, Gobec et al [ 24 ] obtained the ethyl 6-phenylcoumarin-3-carboxylate 9a with only 33% yield, while the reaction time was not specified (overnight); Carbonaro et al [ 23 ] reported the formation of product 9a in 55% yield for 12–16 h. In the procedure that we developed, the ethyl 6-phenylcoumarin-3-carboxylate 9a was isolated with 90% yield after only 30 min, entry 1 ( Table 4 ). The yield of compound 9c was reported to be 67% (overnight) [ 24 ] and 66% (12–16 h) [ 23 ].…”

“…For example, Gobec et al [ 24 ] obtained the ethyl 6-phenylcoumarin-3-carboxylate 9a with only 33% yield, while the reaction time was not specified (overnight); Carbonaro et al [ 23 ] reported the formation of product 9a in 55% yield for 12–16 h. In the procedure that we developed, the ethyl 6-phenylcoumarin-3-carboxylate 9a was isolated with 90% yield after only 30 min, entry 1 ( Table 4 ). The yield of compound 9c was reported to be 67% (overnight) [ 24 ] and 66% (12–16 h) [ 23 ]. Using the optimized procedure based on the PEPPSI-type catalyst, we managed to isolate the ethyl 6-(4-methoxyphenyl)coumarin-3-carboxylate 9c in 92% for 45 min, entry 6 ( Table 4 ).…”

“…However, most of these synthetic protocols are focused on monosubstituted coumarins. Only limited applications of metal-catalyzed reactions for the synthesis of benzene ring-functionalized 3-substituted coumarins, especially when electron withdrawing groups are present, have been reported [ 23 , 24 , 25 ]. Therefore, herein we present an efficient method for the synthesis of fluorescent coumarins and phosphorous-containing coumarin-type heterocycles via palladium cross-coupling reactions, whereby the visible absorption properties of the compounds can be controlled by introducing various C-3 and C-6 substituents directly to the heteroaromatic structure.…”

Crystallography-based exploration of non-covalent interactions for the design and synthesis of coumarin for stronger protein binding

“…19 The light absorption and emission wavelength varied over a long range depending upon the nature of substituents. 19,20 These are the main reasons why these compounds are designed for multiple applications like biomarkers, cell imaging, sensors in living cells, and various other applications. [19][20][21] For a desirable biological application of these compounds, it is often difficult to choose a suitable molecule.…”