Influence of the Environment on the Excitation Wavelength Dependence of the Fluorescence Quantum Yield of Indole

Abstract

The influence of excitation wavelength, pH, oxygen and solvents, upon fluorescence quantum yields, were measured for i n L k Indole in neutral aqueous solution exhibits the same wavelength dependence as tryptophan, which indicates that COO-absorption is not responsible for the effect. Parameters such as pH and oxygen influence only the absolute fluorescence quantum yields but not their relative variation with wavelength, indicating competition with fluorescence emission for S, deactivation. without any influence upon deactivation of higher excited states. In contrast, solvents exhibit ii specific influence upon the wavelength dependence; for indole. the decrease of fluorescence yield excited around 215 nm, compared with the yield in the first absorption band is about 40% in water. 10% in acetonitrile, 70% in n-hexane and cyclohexane, whereas no appreciable decrease occurs in methanol, ethanol or n-butanol. These observations, together with the Stokes shifts of the emission spectra, may be well correlated with Kosower's Z-values, expressing microscopic solvent-solute interactions.

The role of the molecular environment for the primary photoprocesses of phenol in solution

“…This observation is in broad agreement with the inadequacy of general liquid state parameters, such as the static dielectric constant or Kosower's parameter Z, to account for the observed solvent effect on photophysical and photochemical processes of these compounds, especially in aqueous solutions and in aqueous/organic mixtures. Indeed, a correlation of the data of the present work with these parameters leads to results which are very similar to those reported in the literature for indolic compounds (6,12,13), and which yield little information about the mechanisms responsible for the observed effects.…”

“…The characteristic feature of the excitation energy dependence of the fluorescence of phenolic (2,7) and indolic (3,5,6) compounds is a drop of Q F in the region of overlap between the S, and S, absorption bands. Q F is constant within each absorption band.…”

“…It has been early recogquantum yield as as On nized that this effect is strongly influenced by the photoejection and H atom formation by OH bond solvent environment: the dependence of e F o n ex-rupture has been investigated in pure ~o l a r and citation energy is pronounced in hydrocarbon sol-apolar solvents and in solvent mixtures. Particular vents, small in polar organic solvents, but notable has been paid the possible of again in water (2,6). A correlation between the Specific S~lUte-S~l~ent interactions On these proeffect on QFand the hydrogen bonding capability of cesses.…”

“…Dependence of P on excitation wavelength for phenol (20) cyclohexane; (6) pure diethyl ether. Curves C and E: absorption…”

The incorporation of divalent metal ions into recombinant human tyrosine hydroxylase apoenzymes studied by intrinsic fluorescence and 1H‐NMR spectroscopy

“…Stock solutions of Fe(I1) ammonium sulfate (1 mM) were prepared in water and used within 30 min. The quantum yields of hTHl and hTH2 were determined using free tryptophan as a reference and assuming a quantum yield of 0.13 for L-tryptophan in water [18]. For these determinations, the absorbance of enzyme solutions at 296 nm was < 0.05.…”