Subphthalocyanines, Subporphyrazines, and Subporphyrins: Singular Nonplanar Aromatic Systems

The chemistry of contracted porphyrinoids, subporphyrins (SubPs), subporphyrazines (SubPzs), and subphthalocyanines (SubPcs), has developed extraordinarily during the years. Significant efforts have been directed toward the preparation of new SubPzs that are usually prepared by reacting disubstituted maleonitriles with boron trichloride groups at the axial substitution by nucleophiles. One of the most outstanding applications of SubPcs is their incorporation as small molecules in photovoltaic devices in which generation of electrical current from solar energy takes place. Notable is also the progress in the field of energy and electron transfer in covalent and noncovalent SubPc/fullerene conjugates. The stepwise synthesis of larger systems, dimers, trimers, etc., with well-defined curved fully conjugated π surfaces is something achievable and can give rise to new compounds with interesting spectroscopic features, including Q bands that will be strongly shifted to the red and even near-IR.