The phthalocyanine macrocycle and numbering scheme. The isoindole positions near the ring are often referred to as α (i.e. 1,4,8,11,15,18,22,25) and those away from the ring β. Substitution at the β positions is more typical. For substituted phthalocyanines with an odd number of substituents on the isoindoles there are usually positional isomers, and these isomers are usually not specifically enumerated. PcF16 where all positions bear a fluorine and the Cu(II) complex, are commonly used in photovoltaic applications.