Polymorphic crystallization and crystal-to-crystal thermal phase transition of non-peripherally substituted octahexyl phthalocyanine (C6PcH2) have been investigated. Two types of single crystals, α and β types C6PcH2, were separately grown by controlling the recrystallization conditions, moreover, the structures were determined by single-crystal X-ray structure analysis. The crystal-to-crystal thermal phase transition from α type to β type C6PcH2 was observed by the differential scanning calorimetry and X-ray structure analysis. The mechanism of the selective crystal growth has been discussed by taking the randomness of the alkyl substituted into consideration.
