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

Abstract

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.

Molecular Model of the Ring-Opening and Ring-Closure Reaction of a Fluorinated Indolylfulgide

“…The extraction of excited state vibrational spectra from the transient absorption data follows a procedure similar to that described in ref . The analysis of the temporal evolution of the absorption changes (section 3) shows that the transient signal at early delay times (about 0.5 ps) consists predominantly of the negative ground state bleach and the induced excited state absorption of the reactant.…”

“…Comparison between experimentally obtained and calculated ground and excited state vibrational spectra for the C-form (a,c) and the cZc/tZc-forms (b,d). Experimental excited state spectra (c,d) are extracted from the transient absorption data at 0.5 ps delay time according to a procedure similar to that described in ref (black traces). Theoretical spectra are obtained from a frequency analysis at the local minima in the excited state Min C , Min cZc , and Min tZc (color traces).…”

Non-classical disproportionation revealed by photo-chemically induced dynamic nuclear polarization NMR

“…4) prompted us to perform quantum-chemical computations at the density-functional theory (DFT) level to calculate the necessary values. Starting point for geometry optimization was a previously published structure model of 6,7,8-trimethyllumazine along with six coordinating water molecules (Schreier et al, 2011). Calculated g iso values were 2.0031 for the neutral radical TML ox q and 2.0034 for the anionic radical TMLH red q − .…”

Hydrogen bond effect on the photophysical properties of 2-ureido-4[1H]-pyrimidinone quadruple hydrogen bonded systems

“…1,18,19 In recent years, the electronic excited-state H-B has been widely investigated with powerful experimental methods, such as time-resolved infrared vibrational spectroscopy, femtosecond uorescence upconversion and transient absorption spectra, and state-of-the-art theoretical methods. [20][21][22][23][24][25][26][27] Han and co-workers 1,28-32 have theoretically and experimentally investigated the excited-state intermolecular H-B dynamics and demonstrated the signicant role of the electronic excited-state H-B on photophysical processes including PET, ICT and metal-to-ligand charge transfer. In particular, they are the rst ones to suggest the PET mechanism facilitated by H-B for uorescence quenching, 31,32 which has been widely used in explaining sensing mechanism for various uorescent probes; they also provided a rule where the intermolecular H-B strengthening/weakening corresponds to red-shis/blue-shis in the electronic spectra.…”