We used harmonic-content frequency-domain fluorometry to investigate the quenching of indole fluorescence by iodide and acrylamide in aqueous solution. The time-resolved intensity decays were recovered from the frequency response of the fluorescence emission, measured over a frequency range from 10 to 2000 MHz. In the absence of collisional quenching the decay of indole in water is predominately a single exponential. The intensity decays became increasingly nonexponential when quenched by either iodide or acrylamide. We attribute the complex decays to transient effects, as predicted originally by Smoluchowski. At quencher concentrations below 0.1 M the decays are of the form exp(−t/τ − 2bt 1/2 ), which is known to be an approximate model. At quencher concentrations above 0.1 M this decay law does not account for the data. The data are in better agreement with the radiation model, and the diffusion coefficients and interaction radii are more reasonable. However, in aqueous solution above 0.5 M acrylamide there appear to be deviations from the radiation model. The deviations are less apparent at high iodide concentrations. For comparison with future theoretical developments, the intensity decay laws are reported up to 0.5 M iodide or 0.7 M acrylamide. Evidently, the resolution and sensitivity of the frequency-domain method are adequate to recover the complex subnanosecond decays found at high concentrations of quenchers.Registry No.
The effect of temperature on the fluorescence properties of 1,8-diphenyl-1,3,5,7-octatetraene (DPO) in polyvinyl alcohol) film (PVA) was investigated in the range from 295 to 428 K. Upon heating above 353 K, the quantum yield of D PO increases rapidly. This effect is irreversible, similarly as the optical density in the long wavelength absorption band (320-440 nm). It has its origin in the cis-trans conversion of DPO molecules in PVA film at high temperatures. The behaviour of the fluorescence anisotropy in the same temperature range was also investigated. The emission anisotropy was found to be a viscosity indicator in the microenvironment of the DPO molecules in PVA film.
Absorption and fluorence spectra of a series of 5-phenyltetrazole derivatives have been measured. Compounds carrying electron-accepting CN or CÖOH groups in the phenyl ring exhibit dual fluorescence. Investigations carried out in acid and basic media and a comparison of the fluorescence of p-cyano-5-phenyltetrazole and l-methyl-5-(4'-cyano) phenyltetrazole show the anions of respective 5-phenyl-tetrazole derivatives to be responsible for the long-wave fluorescence (Amax ^ 400 nm). The long-wave fluorescence of some 5-phenyltetrazole derivatives is associated with a considerable charge derealization between the tetrazole and phenyl rings, this being accompanied by mutual twisting of the rings in the excited state. This finding has been confirmed by the absence of the long-wave fluorescence in rigid media.
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