Tuning Solid‐State Fluorescence in BODIPY Dyes through Substitution‐Controlled Packing Motifs

Understanding how molecular packing governs solid‐state fluorescence is key to unlocking new emissive materials. A comprehensive study of BODIPY derivatives with diverse substitution patterns is presented, showing how these modifications govern intermolecular interactions, packing motifs, and ultimately photophysical behavior in the solid state. Substituent effects dictate whether π–π stacking, hydrogen bonding, or halogen interactions dominate, resulting in distinct emission shifts and variations in fluorescence quantum yield. While increased chromophore overlap often leads to bathochromic emission, it also correlates with reduced quantum efficiency because of enhanced non‐radiative relaxation processes. Notably, compounds with similar degrees of overlap can exhibit different emission profiles, underscoring the pivotal role of substituent‐controlled packing. These insights provide a foundation for rational design of solid‐state luminescent materials based on BODIPY scaffolds.