Tyagi, Amit and Penzkofer, Alfons (2011) Absorption and Emission Spectroscopic Characterization of Lumichrome in Aqueous Solutions. PHOTOCHEMISTRY AND PHOTOBIOLOGY, 87 (3). pp. 524-533. ISSN 0031-8655,
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The spectroscopic behavior of lumichrome (7,8-dimethyl-alloxazine, LC) in aqueous solutions in a pH range from -1.08 to 14.6 is studied. Absorption spectra, fluorescence quantum distributions, quantum yields, and lifetimes are determined. The ionization stage of ground-state LC changes with rising pH from the cationic form (LCH(2)(+)) to the neutral form (LCH) with a mid-point pH of pKc approximate to -0.53, and to the anionic form (LC(-)) with a mid-point pH of pK(a) approximate to 12.5. Above pH 7 a partial ground-state tautomerization of LCH to 7,8-dimethyl-isoalloxazine (IAH) occurs by N1-N10 intra-molecular proton transfer. For pH > pK(a) approximate to 12.5 LCH and IAH change to the anionic forms LC(-) and IA(-), and above pH 14 LC(-) tautomerizes completely to IA(-). In the excited state some neutral lumichrome (LCH*) converts to cationic lumichrome (LCH(2)(+)) at low pH by proton transfer from H(3)O(+) to LCH*. No photoinduced excited-state tautomerization of lumichrome was observed. LCH for pH > 3 and IAH are reasonably fluorescent. The fluorescence efficiencies of LC(-) and IA(-) are lower than those of LCH and IAH. The fluorescence of LCH(2)(+) is strongly quenched likely by intra-molecular diabatic charge transfer and excited-state relaxation by potential surface touching with the ground state.
| Item Type: | Article |
|---|---|
| Uncontrolled Keywords: | LASER FLASH-PHOTOLYSIS; PHOTOPHYSICAL PROPERTIES; SOLVATION DYNAMICS; FLUORESCENT-PROBE; ELECTRON-TRANSFER; PH-DEPENDENCE; BLUF DOMAIN; RIBOFLAVIN; PHOTOTAUTOMERISM; FLAVINS; |
| Subjects: | 500 Science > 530 Physics |
| Divisions: | Physics > Institute of Experimental and Applied Physics > Alumni or Retired Professors > Group Alfons Penzkofer |
| Depositing User: | Dr. Gernot Deinzer |
| Date Deposited: | 22 Jun 2020 05:25 |
| Last Modified: | 22 Jun 2020 05:25 |
| URI: | https://pred.uni-regensburg.de/id/eprint/20900 |
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