Abstract The rate constant for transfer of electronic excitation energy from the first excited singlet state of the solvent toluene to two indoles, l‐p‐chlorophenyl‐S‐benzyloxy‐2‐phenylindole and 5‐methyl‐3‐phenylindole‐ l ‐propionitrile, as solutes in three types of solvent media, pure toluene, 1:9 mixture of toluene and cyclohexane, and 1:9 mixture of toluene and liquid paraffin is determined as a function of temp. in the range 293‐353 Kunder oxygen‐free conditions.
It is demonstrated that the halflife of 232Th can be determined by dissolving a known amount of Th(NO3)4⋅4H2O in a liquid scintillator and using a difference method to obtain the counting rate due to and particles.(AIP)
The absorption spectra of two new indoles, 2-carbethoxy-4-aminoindole and 2-carbethoxy-5-chloro-7-aminoindole are studied in non-polar, polar, dilute and concentrated acidic solvents. The nature of the electronic transitions are identified. The role of substitution groups and the effect of protonation are discussed in interpreting the solvent effects.
A laboratory experiment, using the single-photon counting technique, to determine the fluorescence spectrum of NaI(Tl) crystal under gamma excitation, is discussed.
The rate constant for transfer of electronic excitation energy from the first excited singlet state of the solvent toluene to two indoles, 1-p-chlorophenyl-5-benzyloxy-2-phenylindole and 5-methyl-3-phenylindole-1-propionitrile, as solutes in three types of solvent media, pure toluene, 1:9 mixture of toluene and cyclohexane, and 1:9 mixture of toluene and liquid paraffin is determined as a function of temperature in the range 293–353 K under oxygen-free conditions. The diffusion coefficients of the interacting molecules are measured in situ at ambient temperature. The rate constant is found to vary, in the case of each of the six systems, linearly with the sum of the diffusion coefficients of the two interacting molecules; from this linear variation the contributions of molecular diffusion and excitation energy migration to the rate constant are quantitatively estimated. The results indicate that energy migration involves weak multipole–multipole interaction between an excited and an unexcited solvent molecule, and not successive excimer formation and dissociation. Unique values of the energy migration coefficient and the effective distance at which the solvent–solute energy transfer takes place in the final step, are evaluated in the case of all the six systems; these values are model independent. The final step in energy transfer essentially involves long-range interaction. Dependence of energy migration coefficient and the effective energy transfer distance on environment is discussed.
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