Spectrum of copper phthalocyanine: Experiments and semi-empirical quantum chemical calculations

We investigate the spectrum of copper phthalocyanine (CuPc) both experimentally and theoretically, which is a potential laser protective organic absorbing dye. The observed visible absorption maximum is located at 658 nm, which corresponds to a1u→eg electronic transition. We then theoretically investigate the electronic spectrum of CuPc. By setting OWFπ–π (π–π overlap weighting factor, one of the adjustable parameters in the ZINDO/S method) at 0.522, the visible absorption maximum of CuPc is precisely calculated using the ZINDO/S method. The result shows that the calculated visible absorption maximum is well consistent with the experimental value. Finally, we discuss the validity and applicability of Yuan's calculation formula [J. Phys. Chem. A 109 (2005) 2582], and investigate the new relationship between OWFπ–π and molecular structural parameters for the other metal phthlocyanine series.