Abstract
Near-IR dyes are required for various advanced technologies. Phthalocyanines (Pcs) show intense absorptions in the visible region (the so-called Q band), which can be shifted to the near-IR region by making some changes to the structure. The Q band is composed mainly of the HOMO - LUMO transition. Since the size of the carbon atomic orbital coefficients of α-positions are large in the HOMO, we anticipated that the introduction of an electron donating group to the α-positions will destabilize the energy of the HOMO level significantly. In a similar anticipation, the insertion of a high-valence element (as an electron withdrawing group) into the central cavity appears to stabilize the energy of the LUMO level. As a result, a decrease of the HOMO - LUMO gap is inferred, resulting in a shift of the Q band to longer wavelength. On the basis of this concept, we designed and synthesized some Pcs absorbing in the near-IR region.
