Polarized, V-Shaped, and Conjoined Biscoumarins: From Lack of Dipole Moment Alignment to High Brightness

Abstract

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.

Janus-Type AIE Fluorophores: Synthesis and Properties of π-Extended Coumarin-Bearing Triskelions

“…Their photophysical properties are promising for laser dyes [ 9 , 10 , 11 ], molecular sensors [ 12 , 13 , 14 ], and solar cells [ 15 ]. Furthermore, numerous extended coumarin dyes have been synthesized, and the photophysical properties based on their rigid and planar structures have been described [ 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 ]. Conversely, unusual coumarin dyes with helical geometries have also been reported; these compounds represented a platform for the development of molecular chiral dopants [ 25 , 26 , 27 ].…”

AIEE-active V-shaped fused-biscoumarins: synthesis, photophysical and electroluminescence properties

“…[19][20][21][22][23] Heterocycle-fused coumarin derivatives with the p-extended conjugation systems possess promising photophysical properties in comparison with the simple coumarin derivatives. [24][25][26][27][28][29][30] Among the heterocycle-fused coumarins, V-shaped fused-biscoumarins have attracted significant attention due to their distinguished properties, such as bathochromic-shift in the emission and excitation wavelengths, colorimetric properties, and larger Stokes shift, [31][32][33][34][35] and the photophysical properties and applications of V-shaped fused-biscoumarins are strongly dependent on the fused coumarin ring systems. However, V-shaped fusedbiscoumarins have larger rigid conjugated planes in comparison with the simple coumarins, and they are more prone to forming strong intermolecular p-p stacking interactions in the aggregated state, resulting in aggregation-induced fluorescence quenching, which could limit their application in the field of organic optoelectronic devices.…”