OPEN Repository
Welcome to OPEN - the Repository of Open Scientific Publications, run by the Interdisciplinary Centre for Mathematical and Computational Modelling, University of Warsaw, previously operating as the CeON Repository. The Repository enables Polish researchers from all fields to openly share their articles, books, conference materials, reports, doctoral theses, and other scientific texts.
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22976 archived items
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Recent Submissions
Item
Conformation of the Ester Group Governs the Photophysics of Highly Polarized Benzo[g]coumarins
(American Chemical Society, 2023) Szychta, Kamil; Koszarna, Beata; Banasiewicz, Marzena; Sobolewski, Andrzej; O’Mari, Omar; Clark, John A.; Vullev, Valentine I.; Barboza, Cristina A.; Gryko, Daniel T.; Institute of Organic Chemistry, Polish Academy of Sciences; Institute of Physics, Polish Academy of Sciences; Department of Bioengineering, University of California, Riverside, California; Department of Chemistry, Department of Biochemistry, and Materials Science and Engineering Program, University of California, Riverside, California; Department of Physical and Quantum Chemistry, Faculty of Chemistry, Wroclaw University of Science and Technology, Wrocław
Photosensitizers that display “unusual” emission from upper electronically excited states offer possibilities for initiating higher-energy processes than what the governing Kasha’s rule postulates. Achieving conditions for dual fluorescence from multiple states of the same species requires molecular design and conditions that favorably tune the excited-state dynamics. Herein, we switch the position of the electron-donating NMe2 group around the core of benzo[g]coumarins (BgCoum) and tune the electronic coupling and the charge-transfer character of the fluorescent excited states. For solvents with intermediate polarity, three of the four regioisomers exhibit fluorescence from two different excited states with bands that are well separated in the visible and the near-infrared spectral regions. Computational analysis, employing ab initio methods, reveals that the orientation of an ester on the pyrone ring produces two conformers responsible for the observed dual fluorescence. Studies with solid solvating media, which restricts the conformational degrees of freedom, concur with the computational findings. These results demonstrate how “seemingly inconsequential” auxiliary substituents, such as the esters on the pyrone coumarin rings, can have profound effects leading to “anti-Kasha” photophysical behavior important for molecular photonics, materials engineering, and solar-energy science.
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Polarized, V-Shaped, and Conjoined Biscoumarins: From Lack of Dipole Moment Alignment to High Brightness
(American Chemical Society, 2022) Kielesiński, Łukasz; Deperasińska, Irena; Morawski, Olaf; Vygranenko, Kateryna V.; Ouellette, Erik T.; Gryko, Daniel T.; Institute of Organic Chemistry, Polish Academy of Sciences; Institute of Physics, Polish Academy of Sciences; Department of Chemistry, University of California; Chemical Sciences Division, Lawrence Berkeley National Laboratory
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 NO2 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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