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(vin yl) alcohol (PVA) films of different porphyrin derivatives are reporte d, Wavelength dependent absorption anisotropy in oriented PVA films, a nd 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 or ientation. Comparison of linear dichroism and orientation behavior in stretched PVA films of deuteroporphyrin III (C-2V symmetry) and its ir on derivative reveals significant out-of-plane transition moment compo nents. A considerable participation of out-of-plane polarized absorpti on components is also observed for metal derivatives of non-symmetrica l protoporphyrin IX. It appears that central metal substitutions in po rphyrin rings do not produce 'circular' degeneration of electronic tra nsition moments. Instead, the presence of metal induces absorption com ponents orthogonal to the porphyrin plane. (C) 1997 Elsevier Science B .V.