Elucidation of the relationship between solid‐state photoluminescence and crystal structures in 2,6‐substituted naphthalene derivatives

Polycyclic aromatic hydrocarbons (PAHs) are known to exhibit fluorescence in solution, but generally do not emit in the solid state, with the notable exception of anthracene. We previously reported that PAHs containing multiple chromophores show solid-state emission, and we have investigated the relationship between their crystal structures and photoluminescence properties. In particular, PAHs with herringbone-type crystal packing, such as 2,6-diphenylnaphthalene (DPhNp), which has a slender and elongated molecular structure, exhibits red-shifted solid-state fluorescence spectra relative to their solution-phase counterparts. In this study, we synthesized 2,6-naphthalene derivatives bearing phenyl and/or pyridyl substituents (PhPyNp and DPyNp) and observed distinct, red-shifted emission in the solid state compared with that in solution. Crystallographic analysis revealed that both PhPyNp and DPyNp adopt herringbone packing motifs. These findings support our hypothesis that the spectral characteristics of PAH emission are closely linked to crystal packing arrangements, providing a useful strategy for screening PAH candidates for applications in organic semiconducting materials.