Three‐Component Synthesis and Photophysical Properties of Novel Coumarin‐Based Merocyanines

Abstract

Novel E-configured coumarin-based merocyanines were efficiently synthesized by a one-pot, three-component Sonogashira coupling-Michael addition starting from triflyl coumarins, terminal alkynes and secondary amines. The photophysical properties of the synthesized yellow to orange merocyanines were studied by UV/Vis and fluorescence spectroscopy and rationalized by Hammett-Taft correlations and DFT and TD-DFT calculations. Most compounds were only weakly fluorescent in solution; however, two compounds were investigated in more detail with respect to their aggregation behavior. The system for R =H and NR =pyrrolidinyl shows aggregation induced emission at a water content of 40-60 % in methanol, while the chromophore with R =p-Me NC H and NR =morpholinyl displays considerable aggregation induced emission enhancement with a concomitant redshift at increasing water contents in THF.

Synthesis and Studies on Photophysical Properties of Rhodamine Derivatives for Bioimaging Applications

“…In all three compounds, the effect of the solvent polarity on the emission spectra was more prominent than absorption spectrum, it is due to the intramolecular charge transfer (ICT) effect . The change in the polarity of solvent used for fluorescence emission study induces the change in the little spectral shift by 2–20 nm for all the compounds …”

“…26,35 The absorption maximum of RHB1 changes from 560 nm (DCM) to 562 nm (methanol), except in polar aprotic solvents (acetone) other solvents do not show an absorption band. [27][28][29][30] Table 1 shows the photophysical parameters including absorption and fluorescence maxima, molar extinction coefficients, Stokes shifts and fluorescence quantum yields for each rhodamine derivatives. The fluorescence emission bands are broad in nature and shows wide spectral visible region from 500 to 650 nm for RHB1, from 520 to 650 nm for RHB2, and from 540 to 650 nm for RHB3 in a variety of solvent.…”

Solid State and Aggregation Induced Emissive Chromophores by Multi‐component Syntheses

“…[18] The resulting covalently bound dye-polymer hybrids are yellow to red and solid state fluorescence spectroscopy reveals that highest quantum yields up to 16 % are found at lowest dye content. [19] Besides elaboration of the electronic substituent effects on absorption, emission and Stokes shifts by Hammett-Taft correlations and quantum chemical calculations on the predominantly weakly to moderately emissive merocyanines, two systems with pronounced AIE behavior were identified and characterized. 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 Employing triflyl coumarins 10 as pseudohalide coupling partners permits the vinyloguous extension of enaminocarbonyl systems.…”

Three-Component Suzuki–Knoevenagel Synthesis of Merocyanine Libraries and Correlation Analyses of Their Oxidation Potentials and Optical Band Gaps

“…Besides MCR syntheses of indolone [ 25 , 26 , 27 ], aroyl [ 28 , 29 ] and coumarin [ 30 ]-based merocyanines, we just recently communicated the versatile access to DSSC (dye sensitized solar cell) merocyanines bearing carboxylic acid end groups for immobilization on TiO 2 by a consecutive three-component Suzuki–Knoevenagel condensation sequence [ 31 ].…”