The linear dichroism spectra of free base and manganese(III) porphyrins

Effect of central metal substitution on linear dichroism of porphyrins: evidence of out-of-plane transition moments

Absorption anisotropy and emission anisotropy measurements in poly(vinyl) alcohol (PVA) films of different porphyrin derivatives are reported. Wavelength dependent absorption anisotropy in oriented PVA films, and wavelength dependent excitation spectrum of emission anisotropy of fluorescent porphyrin derivatives in isotropic PVA films indicate the presence of multiple transition moments with different well-defined orientation. Comparison of linear dichroism and orientation behavior in stretched PVA films of deuteroporphyrin III (C2V symmetry) and its iron derivative reveals significant out-of-plane transition moment components. A considerable participation of out-of-plane polarized absorption components is also observed for metal derivatives of non-symmetrical protoporphyrin IX. It appears that central metal substitutions in porphyrin rings do not produce 'circular' degeneration of electronic transition moments. Instead, the presence of metal induces absorption components orthogonal to the porphyrin plane.

Orientation and mobility of molecules in membranes studied by polarized light spectroscopy

Biological membranes are composed of mainly lipids and proteins. The physical properties of the lipids, forming a bilayer structure, are of crucial importance for the living cell, since the plasma membrane is the guardian barrier towards the environment. Thus, the functioning cell needs a highly stable lipid bilayer, which depends on molecular packing and orientation properties of the various membrane components (Wieslanderet al.1980). The spatial arrangement of the membrane proteins incorporated in the lipid matrix plays an essential role for the different chemical processes occurring at or within the membrane. Information about molecular orientation and mobility is therefore necessary for unravelling the functional mechanisms of a biological membrane.

Spectral properties of chlorophyll a in liquid crystal

Solution of chlorophyll a in liquid crystals mixture (MBBA + EBBA) was investigated. Chl molecules are in LC in low electric field oriented. They can be divided into two groups: one strongly interacting with LC and subjected to reorientation by the electric field, and another weakly interacting with the solvent and insensitive to the voltage applied. The emission spectrum of the first type of chlorophyll is strongly perturbed. At higher voltages, the pigment molecules orientation in the plane of the electrode is another. Pigment absorption and emission anisotropy provides information about the reorientation of LC molecules. Even at high (10(-3)M) Chl concentration and regular pigment array, the interaction between the pigment and solvent exceeds pigment-pigment interaction because the solvent appears to have a stronger influence on the Chl spectrum.