Phthalocyanines: The need for selective synthetic approaches

Recent years have witnessed increasing interest in the synthesis of low-symmetry single phthalocyanines (Pcs) since they may show, among other applications and advantages, interesting second-order nonlinear optical (NLO) properties, This potential of unsymmetrically substituted and regioisomerically pure phthalocyanines has motivated researchers in this field to develop selective methods for synthesizing macrocycles of this type. In this microreview, we focus on the approaches reported by other research groups as well as ourselves that allow the predominant or exclusive formation of the required compounds. The selective preparation of differently substituted or intrinsically unsymmetrical Pc-related systems and Pc homologues is also discussed.