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 a(lu) -> e(g) electronic transition. We then theoretically investigate the electronic spectrum of CuPc. By setting OWF pi-pi (pi-pi 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) 25821, and investigate the new relationship between OWF pi-pi and molecular structural parameters for the other metal phthlocyanine series. (c) 2007 Elsevier B.V. All rights reserved.