Concentration Dependency of the Fluorescence from Solutions of 2-Phenyl Indole and Derivatives of 2-Phenyl Indole. I. Fast-Electron Excitation

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Abstract
The relative scintillation yield for excitation with fast electrons was measured as a function of the concentration of the solute. The property of self-quenching of a series of 2-phenyl indole and 2-phenyl indole derivatives was correlated with the structure of the compound. It was shown that destroying the ability of the chromophore of the molecule to obtain a coplanar configuration would eliminate self-quenching in most cases. The exceptions were those derivatives which had an H atom on the N atom of the indole ring. It is believed that in these cases self-quenching may proceed through a hydrogen-bonding mechanism. The substitution on long-chain alkyl groups on the N atom of the indole did not eliminate self-quenching even for a 12-carbon-atom chain. There was a gradual decrease in self-quenching upon increasing the substituent from methyl to n-hexyl.