Relative Interaction Radii for Quenching of Triplethyphen;State Molecules

摘要

The relative efficiencies with which O2, NO, and Xe enhance the transition from the excited triplet state to the ground state in naphthalene have been determined from static experiments. Essentially, the experiments consisted of the observation of the steadyhyphen;state phosphorescent emission intensity and the intensity of the electron spin resonance (ESR) signal of the triplethyphen;state moelcules as functions of added quencher. All measurements were made in 3hyphen;methylpentane (3hyphen;MeP) glass solutions at 77deg;K, where material diffusion is minimized. The data were analyzed in terms of the expressionNthinsp;sol;thinsp;N0thinsp;equals;thinsp;explcub;thinsp;minus;thinsp;lsqb;0.0025lpar;Rqrpar;3Cqrsqb;rcub;, whereNandN0are the steadyhyphen;state naphthalene triplethyphen;state concentrations in the presence and absence of added quencher, respectively,Rqis an effective interaction distance for the quenching process, andCqis the concentration of added quencher. This equation has previously been shown to be an adequate approximation for interaction mechanisms that are controlled by electron exchange overlap integrals. The values ofRqderived from the experimental data are 10.5thinsp;plusmn;thinsp;0.3, 13.1thinsp;plusmn;thinsp;0.2, and 5.8thinsp;plusmn;thinsp;0.4 Aring; for O2, NO, and Xe, respectively. Corresponding values for quenching of phenanthrene triplethyphen;state molecules by naphthalene and for naphthalenehyphen;naphthalene energy transfer are 13.6thinsp;plusmn;thinsp;0.1 and 12thinsp;plusmn;thinsp;1 Aring;, respectively. Analysis of the emission and ESR data shows that the mechanisms of quenching by NO and O2are essentially radiationless while the Xe perturbation affects mainly the radiative transition probability. The derived results are discussed in terms of triplethyphen;state quenching by energy transfer to the quencher and by the enhancement of intramolecular triplethyphen;singlet intersystem crossing. Since NO does not have the necessary energy levels for energy transfer from naphthalene to proceed, the result that the value forRqfor NO is larger than that for O2indicates that energy transfer probably does not occur in the O2case either.