Tailoring the Solid‐State Fluorescence Emission of BODIPY Dyes by meso Substitution

4,4-Difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) derivatives bearing varied substituents at the meso position (i.e., CF3 , CH3 , COOR, CHO, CN, Cl, iPr) were synthesized to elucidate the structure-property relationships that give rise to emissive J-aggregates. Several new BODIPY derivatives can be added to the previously reported 1,3,5,7-tetramethyl-8-trifluoromethyl derivative to the list of those forming J-aggregates, in addition to other dyes that are emissive in the solid state without forming J-aggregates.