Orientation Effects on C2(5)-C2ʹ(5ʹ) Linked Bioxazole Isomers Synthesized Via Regioselective and Sequential CH Arylation

Bis(4-fluorophenyl) substituted oxazole (2,5-Oxz) and C2(5)-C2ʹ(5ʹ) linked bioxazole isomers (C2-C2ʹ_BOxz, C2-C5ʹ_BOxz and C5-C5ʹ_BOxz) were concisely synthesized via palladium-catalyzed regioselective and sequential CH arylation in 1–3 reaction steps along with 20%–83% of total yields from oxazole and 4-bromofluorobenzene. The linking orientation plays a key role in the packing geometry and photophysical properties of C2-C2'_BOxz, C2-C5'_BOxz and C5-C5'_BOxz. These bioxazole isomers in solid state showed significant differences in photoluminescence quantum yields (PLQY) (0.33, 0.25 and 0.04, respectively), delayed fluorescence properties and powder X-ray diffraction (PXRD) patterns, suggesting the divergence in intermolecular interactions. The theoretically calculated gradient isosurfaces and complexation energies indicate the existence of intense π-π interactions between molecular layers, which are in good agreement with the variation trend of optical properties.