Fluorescence Quenching by Oxygen of 9,10-Dimethylanthracene in Liquid and Supercritical Carbon Dioxide

Abstract

The contribution of diffusion to the fluorescence quenching by oxygen of 9,10-dimethylanthracene (DMEA) in liquid CO2 and supercritical CO2 (SCF CO2) at pressures up to 60 MPa was investigated. For comparison, the fluorescence quenching by CBr4 of DMEA was also investigated. The apparent activation volume of the quenching rate constant, k q, was 8 ± 1 and 10 ± 3 cm3/mol for DMEA/O2, and 42 ± 7 and 400 ± 90 cm3/mol for DMEA/CBr4 in liquid CO2 (25 °C, 10 MPa) and SCF CO2 (35 °C, 8.5 MPa), respectively. For DMEA/O2, the plots of ln k q against ln η, where η is the solvent viscosity, showed a leveling-off with decreasing the solvent viscosity, whereas for DMEA/CBr4 they were almost linear in both liquid and SCF CO2. The results, together with those of the pressure and the pressure-induced solvent viscosity dependences of k q for DMEA/O2 in n-alkanes (C4 to C7) and for DMEA/CBr4 in n-hexane, revealed that the quenching competes with diffusion. The contribution of diffusion to the quenching was analyzed on the basis of a kinetic model with solvent cage in which the quenching occurs. The bimolecular rate constant for the quenching in the solvent cage, k bim, was 6.0 × 1010 and 12 × 1010 M-1 s-1 in liquid CO2 (25 °C, 10 MPa) for DMEA/O2 and DMEA/CBr4, respectively, and 5.7 × 1010 and 12 × 1010 M-1 s-1 in SCF CO2 (35 °C, 8.5 MPa) for DMEA/O2 and DMEA/CBr4, respectively. The pressure dependence of k bim and the contribution of diffusion to the quenching are discussed.

Inverse correlation between efficiency of singlet oxygen production and rate constant for oxygen quenching in the S1 state of anthracene derivatives

“…1,2 It was demonstrated for many molecules that k S q was approximately a diffusion-controlled value whereas the rate constant (k T q ) for oxygen quenching of the lowest excited triplet state (T 1 ) was roughly 1/9 of k S q , and this observation was explained reasonably in terms of the difference of spin-multiplicity in the energy transfer from the two excited states to oxygen. As shown in previous papers, [3][4][5][6][7] k S q of anthracenes substituted at the meso-position depends significantly on the electron-donating character of the substituent and is fairly smaller than a diffusion-controlled limit for the derivatives possessing electron-withdrawing substituents such as 9,10dicyanoanthracene (DCNA), CNA and DCLA.…”

“…The values of F 0 T for solutions containing no oxygen are determined by eqn. (5) from the ratio of U s to total heat released (U t ),…”

Photophysical Detection of Singlet Oxygen

“…Another derivative of anthracene i.e. 9,10-dimethyl anthracene (DMA) reacts almost irreversibly with 1 O 2 in various organic and aqueous medium with a significantly high rate constant (6.8 × 10 7 -5.7 × 10 10 M −1 S −1 ) with the result of producing non fluorescent 9,10-endoperoxide [21][22][23][24]. Elim Albiter et.al reported a facile photosensitized oxidation of 9,10 demethylanthracene with 1 O 2 in presence of safranin O/ silica composite as a heterogeneous photosensitizer [21] in which they reported that oxidation rate does not depend on surface of the composite rather depend only the initial concentration of DMA, light intensity and the amount of composite formed.…”

Contribution of local density augmentation in the vicinity of 9-cyanoanthracene and dynamic fluorescence quenching by oxygen in liquid and supercritical carbon dioxide

“…22,23 In previous publications, 25,26 the pressure effect on the fluorescence quenching of pyrene by polybromoethanes, Q, with wide quenching ability in liquid solutions has been studied and successfully interpreted on the basis of a kinetic model, which involves the exciplex, (MQ)*, via the encounter complex, 1 (M*Q) en , formed between the lowest excited singlet state, 1 M*, and Q. This model was successfully applied to the fluorescence quenching of DMEA by oxygen (8.5-40.0 MPa) and CBr 4 (8.5-60.0 MPa) 27 and of DCNA by oxygen (8.0-60.0 MPa) 28 in SCF CO 2 at 35 C as well as in liquid CO 2 (10.0-60.0 MPa) at 25 C, and the fluorescence quenching for these systems in SCF CO 2 was shown to be interpreted in the same framework as that in liquid CO 2 , indicating no contribution of local composition enhancement to the quenching in the pressure range examined.…”