Optical properties of phthalocyanine and naphthalocyanine compounds

Phthalocyanines, naphthalocyanins, and their derivatives are frequently used as light modulating materials. These compounds, with their stable planar square structure and highly delocalized pi-electron system, are being used in numerous technological applications, such as pigments in chemical sensors, and more recently as photosensitizers for photodynamic therapy. The nonlinear optical properties (NLO) of these compounds are of particular importance. Using density functional method (DFT), we calculated the optical properties of phthalocyanine and naphthalocyanine complexes with Si as a central atom. We examined the effect of hydrophilic axial substituents and the size of polycyclic aromatic hydrocarbons surrounding the porphyrazine-Si kernel on the optical properties of title molecules. Both UV-vis and RSA spectra are calculated and are compared with available experimental results. The time-dependent DFT (TDDFT) with the B3LYP functional predicts that the characteristic UV-vis absorption maxima are blue-shifted; however, the relative error is almost constant for phthalocyanine and naphthalocyanine compounds. The TDDFT triplet-triplet absorption spectra of Si-phthalocyanine and Si-naphthalocyanine complexes reproduce experimental data well.