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

• The absorption properties of eight dye compounds are calculated.
• The effect of the substituted sites on porphyrin-based compounds is revealed.
• A relation between metal d orbital populations and absorption properties is found.
• A metal phthalocyanine derivative with IR absorption spectrum is designed.

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 104 L/mol cm. Moreover, the intrinsic reasons for the significant absorption properties for the phthalocyanine-based compounds were revealed.

The electronic transition properties of eight porphyrin-based and phthalocyanine-based compounds are specially calculated by the density functional and its time dependent theory calculations. It is found that the substituted positions of the functional groups influence the NIR absorption properties of compounds. The relations between the absorption efficiency and the substituted positions of functional groups are revealed, and more efficient phthalocyanine-based dyes are designed.Figure optionsDownload as PowerPoint slide