Spectroscopic and structural properties of phthalocyanines deduced from their frontier molecular orbitals (MOs) and MO calculations

The variation in redox potentials of low-symmetry metallophthalocyanines (MPcs) can be deduced by carefully observing the shape of the frontier MOs, thus proving the existence of a close relationship between MOs and redox potentials. Pcs having the main band (Q-band) beyond 1000 nm were designed and substantiated based on consideration of the size of coefficients of the MOs. Geometrical isomers of Pc derivatives can be discriminated (or identified) by MO calculations since experimental IR spectra can be convincingly well reproduced by calculated IR spectra. Similarly, it is shown that enantiomers can be identified by MO calculations since the calculated band intensities and centers were in close agreement to the experimental data. Some representative absorption spectra of 4nπ porphyrinoids including Pcs are introduced and a method of interpretation using six frontier orbitals is presented.