The most common strategy for the formation of low symmetry Pc's based on peripheral substitution and/or fused ring modification is to carry out condensation reactions with two different precursors to form compounds with AAAA, AAAB, AABB, ABAB, ABBB, and BBBB structures. The effect of lowering the symmetry is more pronounced, in the case of partial peripheral fused ring substitution. Typically, when there is a red shift of the Q band based on a destabilization of the HOMO, there will also be a decrease in the first oxidation potential, since it is easier to remove an electron. Conversely, a stabilization of the LUMO makes it easier to add an electron and, hence, leads to a decrease in the first reduction potential. The symmetry of radially symmetric phthalocyanines with AAAA structures can be lowered by introducing structural modifications.
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