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.