Substituent-induced circular dichroism in phthalocyanines

Phthalocyanines with two and four optically active binaphthyl units have been synthesized and characterized by electronic absorption, CD, and MCD spectroscopy. The chiral substituents induce CD in the in-plane polarized Q and Soret bands of phthalocyanines: phthalocyanines having R and S binaphthyls show positive and negative CD, respectively. The geometries of the compounds were optimized at the PM3 level, and a vector coupling model for the induction of rotatory strength was developed. This model provides a semi-quantitative description of the CD spectra. Thus, not only the sign of the CD spectra but also the intensity relationship between the Soret and Q CD bands and, further, the shape of the Q CD band were reasonably explained. The discussion focuses on the important role of the central hydrogen atoms.