Fluoresence quenching of benzo(a)pyrene by oxygen and carbon tetrabromide in n-hexane under high pressure: estimation of the diffusion coefficient of quencher

摘要

The contribution of diffusion to the fluorescence quenching by oxygen and carbon tetrabromide (CBr4) of benzo(a)pyrene (BZPY) in n-hexane at pressures up to 400 MPa was investigated. For both BZPY/02 and BZPY/CBr4, the fluorescence quenching rate constant, kq, decreased significantly with increasing pressure. The apparent activation volume for kq, Ll V q # , was 10.1 :1:= 0.1 and 13.2 :1:= 1.0 cm3/mol for BZPY/02 and BZPY/CBr4, respectively. It was also found that the plot of lnkq against In 1), where 1) is the solvent viscosity, showed significant downward curvature. From these Tesults, it was concluded that the quenching competes with diffusion for both of the systems at the lower-pressure region. The contribution of diffusion to the quenching was analyzed on the basis of a kinetic model with solvent cage in which the quenching occurs, and the observed kq was separated into the contributions of the bimolecular rate constant in the solvent cage, kbim, and the rate constant for diffusion, kdiff .By using the values of kdiff thus separated, together with those of the diffusion coefficient of BZPY that was measured by other workers, the diffusion coefficients for 02 and CBr4 were estimated.