Origin of the Q-band splitting in the absorption spectra of aluminum phthalocyanine chloride

The absorption Q-band of aluminum phthalocyanine chloride molecule is very sensitive to the internal geometrical distortion. The time-dependent density functional theory calculations have shown that a change of 1.2° for the α angle costs around 1 kcal/mol in energy, but can induce 12 nm splitting for the Q-band.