Shafikov, Marsel Z. and Brandl, Fabian and Dick, Bernhard and Czerwieniec, Rafal (2019) Can Coumarins Break Kasha's Rule? JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 10 (21). pp. 6468-6471. ISSN 1948-7185,
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Coumarin C-2 was reported (Signore et al., J. Am. Chem. Soc., 2010, 132, 1276 and Brancato et al., J. Phys. Chem. B, 2015, 119, 6144) to break Kasha's rule. However, the two lowest excited singlet states of C-2 are separated by less than 0.5 eV. To slow down the S-2 -> S-1 internal conversion and thus to enable the Kasha's rule-breaking S-2 fluorescence, a much larger energy separation seems to be necessary. Thus, the photophysical behavior reported for C-2 raised very basic questions concerning mechanisms of nonradiative transitions in organic molecules. Herein we reinvestigated luminescence of C-2 and found that thoroughly purified C-2 does not show any dual fluorescence in steady-state experiments, contrary to the previous findings. The higher-energy emission, previously erroneously assigned as S-2 -> S-0 fluorescence of C-2, stems from persistent impurity of the synthetic precursor (C-1).
| Item Type: | Article |
|---|---|
| Uncontrolled Keywords: | INTERSYSTEM CROSSING RATE; DUAL FLUORESCENCE; EXCITED-STATE; EMISSION; AZULENE; RELAXATION; ENERGY; S-2; |
| Subjects: | 500 Science > 540 Chemistry & allied sciences |
| Divisions: | Chemistry and Pharmacy > Institut für Physikalische und Theoretische Chemie |
| Depositing User: | Dr. Gernot Deinzer |
| Date Deposited: | 25 Mar 2020 07:37 |
| Last Modified: | 25 Mar 2020 07:37 |
| URI: | https://pred.uni-regensburg.de/id/eprint/25850 |
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