Temperature dependence of the nearly diffusion-controlled fluorescence quenching by oxygen of 9,10-dimethylanthracence in liquid solution

Abstract

The rate constant, for the Ñuorescence quenching of 9,10-dimethyl-anthracene (DMEA) by oxygen in k q , n-hexane and methylcyclohexane (MCH) was measured as a function of temperature at 0.1 MPa. It was found that the activation energy for the quenching, was 6.6^0.1 and 8.4^0.3 kJ mol~1, smaller than that for E q E, the solvent viscosity, 7.1^0.2 and 10.6^0.1 kJ mol~1, in n-hexane and MCH, respectively. The E i E, di †erence between and was interpreted to arise as a result of the quenching being not fully but nearly E q E E i E di †usion-controlled. The contribution of di †usion to the quenching was analyzed quantitatively from the temperature dependence of the solvent viscosity together with that of the radial distribution function at the closest approach distance with hard spheres. The results were shown to be consistent with those obtained from the high-pressure study reported previously.

Contribution of Diffusion to the Quenching by Oxygen of the Lowest Electronically Excited Singlet and Triplet States of Aromatic Molecules in Liquid Solution under High Pressure

“…Recently, we showed that α ex depends slightly on pressure and is expressed approximately by a polynomial in terms of γη for MCH with large pressure induced solvent viscosity dependence at a constant temperature . In this work, α ex was assumed by Substituting eq 10 into eq 9, we have The plots of γ/ against γη are shown in Figure , together that for pyrene reported previously .…”

“…Very recently, the quenching of the S 1 state of pyrene, − 9,10-dimethylanthracene, − and benzo[ a ]pyrene by oxygen as well as heavy atom quenchers at high pressure was examined, and it was shown that can be separated into the bimolecular rate constant for diffusion, k diff , and that for the quenching, k S,bim , in the solvent cage from the analysis of the pressure-induced solvent viscosity dependence of k q S . The similar analysis was successfully applied for the triplet−triplet annihilation of 2-acetonaphthone that is believed to be diffusion-controlled.…”

Solvent and Pressure Effects on Quenching by Oxygen of 9,10-Dimethylanthracene Fluorescence in Liquidn-Alkanes: A Study on Solvent Cage Effects

“…Such cases result from a translational-rotational coupling of diffusion in viscous solvents. We discussed this previously, 20 and R ex was determined by assuming a polynominal in terms of g(σ)η as follows:…”

“…In this work, we measured k q for DMEA/O 2 in liquid ethane and propane for which the size, the viscosity, and the density at a given pressure are smaller than those for the solvents studied previously. 17,20,21 The results, together with those in other n-alkanes and methylcyclohexane (MCH) reported previously, are analyzed by eq 6, and the solvent and pressure (density) dependence of the apparent bimolecular quenching rate constant, k bim,0 , in solvent cage as well as the competition of the quenching with diffusion is discussed.…”

“…In eq 3, R ex is a constant determined experimentally. 16,17,[20][21][22]24 From eqs 2 and 3, we have eq 4.…”