Phthalocyanines: The need for selective synthetic approaches

Recent years have witnessed increasing interest in the synthesis of low-sym metry single phthalocyanines (Pcs) since they may show, among other applica tions and advantages, interesting second-order nonlinear optical (NLO) prop erties, This potential of unsymmetrically substituted and regioisomerically pure phthalocyanines has motivated researchers in this field to develop se lective methods for synthesizing macrocycles of this type. In this microrev iew, we focus on the approaches reported by other research groups as well a s ourselves that allow the predominant or exclusive formation of the requir ed compounds. The selective preparation of differently substituted or intri nsically unsymmetrical Pc-related systems and Pc homologues is also discuss ed.