Unprecedented J‐Aggregated Dyes in Pure Organic Solvents

The design and synthesis of the first organic dyes enabling spontaneous formation of stable J‐aggregates in common organic solvents without additives is described. The new dyes are O‐BODIPYs with a B‐spiranic 4,4‐diacyloxyl substitution pattern. Key to the effectiveness of the J‐aggregation process is the high conformational rigidity of the B‐spiranic molecular design as well as the orthogonal disposition of the B‐diacyloxyl substituent and the meso‐aryl group with respect to the mean plane of the boradiazaindacene. Atomistic simulations, both in vacuum and in a solvent cage, support the dynamics of the J‐aggregation process as well as its dependence on the alkylation pattern of the BODIPY chromophore. A detailed analysis of the photophysical and laser properties of the new dyes provides convincing evidence for the unambiguous assignment of these J‐aggregates and their dependence on the environmental conditions.