Anisotropic rotational behaviour of quinizarin in solution

Abstract

Steady state polarised absorption spectra of quinizarin embedded in stretched polyethylene film and the fluorescence polarisation studies in glycerol indicate that 248, 320 and 470 nm absorption bands are long-axis polarised while that at 280 nm is short-axis polarised. The decay of the emission anisotropy of quinizarin in glycerol, over the temperature range of 15 to 40° C, could be analysed as a double exponential function for all the excitation wavelengths. The calculated rotational correlation times were independent of excitation wavelength, but were dependent on temperature, whereas, the pre-exponential terms were independent of temperature but dependent on the excitation wavelength, as expected from geometrical considerations. The rotational dynamics suggest that the quinizarin molecule rotates as a disk with the slipping boundary conditions and the ratio of the diffusion coefficients about the axes perpendicular and parallel to the plane of the disk is 10 ± 1.