Interplay of Orbital Overlap and Exciton Coupling in the Optical Properties of Adamantylethynyl‐Substituted Pyrene Molecular Crystals

Molecular crystals of apolar π-conjugated hydrocarbons exhibit pronounced solution-to-crystal spectral shifts, yet the interplay between band formation and exciton coupling remains unclear. Adamantylethynyl-pyrene derivatives were designed to adopt unidirectional crystal packing, providing a model system to disentangle these effects. Large redshifts of up to -203 meV are observed, which cannot be explained by exciton coupling alone but require a substantial contribution from band dispersion, identified here as a narrowing of frontier crystal orbital energy levels. The remaining discrepancies between experiment and the full-coherence limit correspond to coherence lengths of four to seven molecules, consistent with literature values. These results provide a basis for interpreting more complex organic crystalline materials and highlight the need for a more comprehensive understanding of the photophysical properties of molecular crystals.