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[Display omitted] • A crystal of the [2.2]paracyclophane-containing organoboron complex shows PFC. • Inter- and intra-molecular π-stacking distances are reduced under high pressure. • The intermolecular π–π interaction is still the important factor leading to PFC. Piezofluorochromism (PFC) of crystals of a tert -butyl and [2.2]paracyclophane-containing diaroylmethanatoboron difluoride (p CP- t Bu), which is expected to possess both intermolecular and intra molecular π–π interactions, was investigated. p CP- t Bu crystals were found to exhibit remarkable PFC associated with an over 150-nm redshift of fluorescence (FL) wavelength occurring under increasing isotropic pressure applied by using a diamond anvil cell. X-ray crystallographic analysis showed that p CP- t Bu molecules in the crystal at atmospheric pressure exist in the form of an intermolecular π-stacking dimer through back-to-back π–π interactions. Moreover, the crystallographic data under high pressure showed that increasing isotropic pressure causes a reduction in both the intermolecular π-stacking distance of the dimer (D INTER) and the intra molecular π-stacking distance between two benzene rings in the [2.2]paracyclophane moiety (D INTRA). Density functional theory calculations, using the Cartesian coordinates obtained by X-ray analysis, suggest that the origin of PFC of p CP- t Bu crystals is the reduction of the LUMO energy of the π-stacking dimer and that the intermolecular π–π interaction is still the important factor leading to PFC of p CP- t Bu crystals. [ABSTRACT FROM AUTHOR]