1-Mono- and 1,7-Disubstituted Perylene Bisimide Dyes with Voluminous Groups at Bay Positions: In Search for Highly Effective Solid-State Fluorescence Materials

A series of 1-mono- and 1,7-disubstituted perylene bisimides (PBIs) with voluminous phenoxy groups at bay positions has been synthesized. These dyes show absorption and emission properties typical for PBIs in solution with high fluorescence quantum yields close to unity. In the solid state, the voluminous substituents at bay positions effectively wrap the dye core and prevent π–π interactions between twofold substituted chromophores. The comparison of UV–vis absorption and fluorescence properties for solutions as well as solid-state thin films, powders, and microcrystals in combination with the respective single-crystal structures allows for establishing the packing structure–optical property relationships. According to this analysis, only with two bulky 2,4,6-tris(4-tert-butylphenyl)-phenoxy or 2,4,6-tris(3,5-di-tert-butylphenyl)-phenoxy substituents functionalized PBI chromophores are completely jacketed to afford efficient solid-state emitter materials with fluorescence quantum yields of over 60%. A comparative evaluation of PBIs bearing bulky substituents at imide positions reveals significantly higher solid-state fluorescence quantum yields of the 1,7-substituted PBIs.