As pointed out in titanylphthalocyanine, molecular distortion (reduction in molecular symmetry) upon crystallization exerts a significant influence on the optical absorption in the near-IR region. The electronic spectra of
Shinya Matsumoto, Jin Mizuguchi, "Molecular Distortion and Exciton Coupling Effects in β Metal-Free Phthalocyanine" in Proc. IS&T Int'l Conf. on Digital Printing Technologies (NIP15), 1999, pp 687 - 690, https://doi.org/10.2352/ISSN.2169-4451.1999.15.1.art00080_2