Synthesis of a Carbazole-[pi]-carbazole Molecular Rotor with Fast Solid State Intramolecular Dynamics and Crystallization-Induced Emission

Herein we report the synthesis of the highly stable crystalline carbazole-based rotor 3 with simultaneous rapid solid state internal rotation and good fluorescence emission. Single crystal and powder X-ray diffraction studies along with microscopy revealed a phase transition from a labile benzene solvate (phase I) to highly stable crystals (phase II) that feature fast intramolecular rotation in the megahertz regime at room temperature, according to variable temperature 2H solid state NMR experiments using isotopically enriched analogues. In addition to the megahertz rotation within its crystals, this crystal phase II displays enhanced solid state fluorescence with a higher quantum yield of ? = 0.28, relative to the emission of this compound in THF solution (? = 0.06). These two solid state properties are significantly different from shorter compounds 1 and 2 (static and nonemissive) included here for comparison purposes.