Orientational distribution of linear dye molecules in bilayer membranes

The fluorescence decay of the linear dye probe DODCI in bilayer membranes is faster in the presence of sucrose in aqueous solution. This is a consequence of the effect of refractive index on the radiative rate of the oriented molecules inside the bilayer. The second-rank order parameter 〈P2(cos θ)〉, determined by the lifetime method, is consistently less than that determined by the anisotropy method. This discrepancy is satisfactorily explained by a bimodal orientational distribution whereas an unimodal distribution is not adequate.