Position of Methyl and Nitrogen on Axial Aryloxy Substituents Determines the Crystal Structure of Silicon Phthalocyanines

Phthalocyanines are a class of organometallic compounds that have been investigated extensively for emerging applications such as organic photovoltaics, organic N-light-emitting diodes, and thin-film transistors. For these applications, the understanding of molecular structures and intermolecular interactions is extremely crucial and is one of Ar-d the most promising pathways for designing a new generation of functional materials. Here, the crystal structures of six axially substituted silicon phthalocyanines (SiPcs) with aryloxy groups are reported. Three bis(methylphenoxy) SiPcs with varying methyl positions and two bis(pyridoxy) derivatives with varying nitrogen positions are compared to the bare bis(phenoxy) SiPc. Quantitative analysis is conducted to describe the impact of the position and nature of the functional group/atom on the orientation of the axial aryloxy subtituents as well as on the aromaticity and planarity of the SiPc macrocycle. Quantitative analysis of changes in intermolecular interactions, in particular, pi-pi interactions, and visual representation using Hirshfeld surfaces are also presented. In all cases, the axial aryloxy substituent determined the solid-state arrangement except for the bis(4-pyridoxy) SiPc, which is isostructural to bis(phenoxy) SiPc.