In its native α-form, pyrene has a herringbone-type crystal packing arrangement, and this αpolymorph transforms to the structurally-related β-polymorph below 163 °C. By crystallizing pyrene from CH2Cl2 at pressures >0.3 GPa, it is possible to crystallize the denser γ-polymorph, which features aligned π-stacked columns of pyrene molecules. However, this structure was reported to dissolve in the crystallization solvent during decompression, making it impossible for us to access this π-stacked polymorph for photochemical experiments. The pyrene derivative, TPhP, crystallizes from CH2Cl2/hexane, to produce a solid which also lacks π-π stacking interactions between pyrene molecules. This is because the phenyl groups frustrate the packing of pyrene cores.