Vibrational Spectra of the Ground and the Singlet Excited ππ State of 6,7-Dimethyl-8-ribityllumazine

• Published in: The journal of physical chemistry. B 2011-04, Vol.115 (13), p.3689-3697
• Main Authors: Schreier, Wolfgang J, Pugliesi, Igor, Koller, Florian O, Schrader, Tobias E, Zinth, Wolfgang, Braun, Markus, Kacprzak, Sylwia, Weber, Stefan, Römisch-Margl, Werner, Bacher, Adelbert, Illarionov, Boris, Fischer, Markus
• Format: Article
• Language: English
• Subjects: B: Biophysical Chemistry; Hydrogen Bonding; Pteridines - chemistry; Quantum Theory; Solvents - chemistry; Spectrophotometry, Infrared; Vibration
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp112126a

6,7-Dimethyl-8-ribityllumazine serves as fluorophore in lumazine proteins (LumP) of luminescent bacteria. The molecule exhibits several characteristic vibrational absorption bands between 1300 and 1750 cm−1 in its electronic ground state. The IR-absorption pattern of the singlet excited ππ* state was monitored via ultrafast infrared spectroscopy after photoexcitation at 404 nm. The comparison of experimentally observed band shifts for a number of isotopologues allows for a clear assignment of several absorption bandsmost importantly the two carbonyl bands. This assignment is confirmed by normal-mode calculations by means of either density functional theory (DFT) calculations for the ground state or the configuration interaction singles (CIS) method for the excited singlet state. A good agreement between experiment and calculation is obtained for models including explicitly a first solvation shell. The results provide a basis for further investigations of lumazine protein and demonstrate the necessity of proper accounting for explicit hydrogen bonding in case of strongly polar molecular systems.