Effect of substituted sites and coordinated metal atoms on the absorption properties of porphyrin and phthalocyanine derivatives.

To design near-infrared (NIR) absorbing photosensitizing compounds, we theoretically elucidated the geometrical structures and electronic transition properties of four porphyrin-based and four phthalocyanine-based derivatives. The results show that fusion of a π-conjugated aromatic ring with the pyrrole rings of porphyrin can cause the larger red-shifts in the Q-bands than π-conjugated groups in the meso positions of porphyrin do. The extent of the red-shift of the absorption bands induced by the coordinated metal atom depends on the electrons occupied in their outer shell. The electron-donating groups also affect the absorption properties of porphyrins due to the σ → π bond formed between the donor groups and the porphyrin ring. Based on these calculated results, we found a phthalocyanine-based compound containing Ti metal that has an absorption wavelength of 977.5 nm and a molar extinction coefficient of 10 4 L/mol cm. Moreover, the intrinsic reasons for the significant absorption properties for the phthalocyanine-based compounds were revealed. [ABSTRACT FROM AUTHOR]