Figure 10 from Polarized, V-Shaped, and Conjoined Biscoumarins: From Lack of Dipole Moment Alignment to High Brightness | Semantic Scholar (2024)

In the effort aiming at the fine-tuning the excited state properties via construction of covalently linked dye assemblies, a novel bis(benzo[g]coumarin), built from two similar moieties that exhibit different degrees of polarization due to the electron donor at positon 8: one possesses a dialkylamino, and the other a weaker amide donor.

The presence of an N—H···O=C intramolecular hydrogen bond in these coumarin–pyrazolone hybrids facilitates excited-state intramolescular proton transfer (ESIPT) and results in the observed correlation between solvatochromism and an increase of fluorescence intensity in polar solvents.

The fluorescence intensity of bis-coumarins linked via CONH and COO functionalities are shown to exhibit a strong dependance on solvent polarity, and the appearance of two fluorescence bands, the relative intensity and spectral positions of which are sensitive to the environment.

The double Knoevenagel condensation of 1,4-dibenzoyloxyanthraquinone with methyl esters of arylacetic acids affords a series of compounds based upon a previously unknown 1,8-dioxa-benzo[e]pyrene-2,7-dione heterocyclic core, which displays a much smaller Stokes shift, yet a markedly increased fluorescence quantum yield.

A highly efficient procedure for the synthesis of bis-coumarins fused at the pyranone ring has been developed, and compounds with four structurally unique skeletons have been obtained and have been shown to strongly absorb in the violet, blue, and/or green regions of the visible spectrum.

It is proven that in non-cyclic, head-to-tail linked tris-coumarins, the photophysics is controlled not only by the substituents but also by the conformation of the molecule, which in turn depends on the nature of the linker's interactions.

The synthesis of a weakly coupled, strongly polarized coumarin dimer has been achieved for the first time using the Skattebøl formylation followed by the Knoevenagel reaction and the formation of a tertiary amide by using a peptide-type procedure.

According to quantum chemical calculations, 3H-chromeno[3,4-c]pyridine-4,5-diones show the specific mechanism of fluorescence quenching, which is related to the intermolecular interaction between adjacent molecules prevailing to a greater extent in the crystal lattice.

A slight variation in the helicities is found to manifest in contrasting excited-state properties of the coumarin-annelated heptahelicenes; in addition to the intramolecular charge transfer (ICT), structural relaxation in the excited state is shown from theoretical calculations to cause decrease in the fluorescence quantum yield for a system with higher helicity.

The efficient syntheses of coumarin-fused helicenes 1’a,b (R=Ph, Me), and the enantioselective synthesis of 1 a (R =Ph) by chiral AuI -catalyzed hydroarylation are reported, and the helical structure of 1 was unambiguously determined by X-ray crystallography.

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