Molecular Luminescence of Some Isoalloxazines in Apolar Solvents at Various Temperatures

Abstract

Abstract— –Spectral properties of isoalloxazines in organic solvents of low polarity are determined at 300 and 77 K. Vibrational structure in the spectra reveals a vibrational mode of 1250cm‐. The pure electronic transition energies are established to a greater accuracy than was done previously and comparison to theoretical data is made. Actual lifetimes up to 10 ns for fluorescence and 300 ms for phosphorescence are found. The ratio of the actual fluorescence lifetime and the radiative lifetime is found to agree well with the quantum yield. Solvent interactions hardly shift the energy of the first electronically excited singlet state but merely affect the Franck‐Condon envelope of the spectrum and the non radiative decay of the chromophore. In albne solutions at 77 K isoalloxazine clusters are formed exhibiting P‐type delayed fluorescence.

On the Enigma of Old Yellow Enzyme's Spectral Properties

“…Although the native enzyme has flavin-like absorption characteristics, there are distinct differences with free FMN under identical conditions, the most important being the considerably red-shifted long-wavelength absorption band : maximumat 21 700cm-'(461 nm)ascomparedto22500cm-' (444 nm) in free FMN [34]. This red shift is considerably larger than usually observed for the isoalloxazine So + S1 transition upon changing the solvent polarity [25,26]. Also the maximum of the near-ultraviolet transition is slightly red-shifted as compared to free FMN, but this behaviour is usual for the isoalloxazine So-+S, transition [28].…”

“…Detailscan be found elsewhere [30]. The pulse repetition frequency was reduced by demodulation as previously [25,26]. The time resolution of the experiment was entirely governed by the Philips XP 2020 detection photomultiplier, which broadened the pulses from the dye laser when observed via an MgO diffuser to 350 ps full width at half maximum.…”

“…of glycerol (Merck, fluorescence microscopy grade). The glycerol used was free from luminescence under irradiation with a 1600-W Xe-arc source, as far as could be established with our detection system capable of determining quantum yields as low as [25,26]. 4-Methoxybenzaldehyde was purchased from Fluka and distilled prior to use.…”

“…Spectra and lifetimes were measured on the same equipment as used previously [25,26]. In the fluorescence lifetime measurements, the extension to longer wavelengths than those available from the CR-5 model argon ion laser was made by the method of synchronous pumping [29,30].…”

Resolution of strongly competitive product channels with optimal dynamic discrimination: Application to flavins

“…26 Although not plainly visible in the liquid-phase spectra, the 0 → 0, 0 → 1, and 0 → 2 vibrational progression of the S 0 → S 1 transition (indicated in Fig. 4) have been observed with a ∼1200 cm −1 spacing through lowtemperature studies, 27 aqueous-phase CARS spectroscopy, 28 and in flavoproteins, where a reduction of inhomogeneous broadening is observed for the flavin chromophore fixed in a protein binding pocket. 29 Specifically, Franck-Condon factors shift the S 0 → S 1 absorption maximum to the 0 → 1 vi- bronic band, while the 0 → 0 vibrational band is visible as a shoulder at ∼475 nm.…”