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Polarized, V-Shaped, and Conjoined Biscoumarins: From Lack of Dipole Moment Alignment to High Brightness
Author(s) -
Łukasz Kielesiński,
Irena Deperasińska,
Olaf Morawski,
Kateryna V Vygranenko,
Erik T. Ouellette,
Daniel T. Gryko
Publication year - 2022
Publication title -
journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.2
H-Index - 228
eISSN - 1520-6904
pISSN - 0022-3263
DOI - 10.1021/acs.joc.2c00232
Subject(s) - chemistry , intramolecular force , solvatochromism , excited state , photochemistry , pyridine , dipole , stokes shift , ground state , conjugated system , molecule , computational chemistry , stereochemistry , fluorescence , organic chemistry , atomic physics , physics , quantum mechanics , polymer
Eleven conjoined coumarins possessing a chromeno[3,4- c ]chromene-6,7-dione skeleton have been synthesized via the reaction of electron-rich phenols with esters of coumarin-3-carboxylic acids, catalyzed by either Lewis acids or 4-dimethylaminopyridine. Furthermore, Michael-type addition to angular benzo[ f ]coumarins is possible, leading to conjugated helical systems. Arrangement of the electron-donating amino groups at diverse positions on this heterocyclic skeleton makes it possible to obtain π-expanded coumarins with emission either sensitive to, or entirely independent of, solvent polarity with large Stokes shifts. Computational studies have provided a rationale for moderate solvatochromic effects unveiling the lack of collinearity of the dipole moments in the ground and excited states. Depending on the functional groups present, the obtained dyes are highly polarized with dipole moments of ∼14 D in the ground state and ∼20-25 D in the excited state. Strong emission in nonpolar solvents, in spite of the inclusion of a NO 2 group, is rationalized by the fact that the intramolecular charge transfer introduced into these molecules is strong enough to suppress intersystem crossing yet weak enough to prevent the formation of dark twisted intramolecular charge transfer states. Photochemical transformation of the dye possessing a chromeno[3,4- c ]pyridine-4,5-dione scaffold led to the formation of a spirocyclic benzo[ g ]coumarin.

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