Nanoscale Organization and Solid-State Dynamics of Carbazole-[π]-Carbazole Rotors Edged with Aliphatic Chains
2018
Aguilar-Granda, Andrés | García-González, Ma Carmen | Pérez-Estrada, Salvador | Kozina, Anna | Rodríguez-Molina, Braulio
The aggregation behavior and its influence on the intramolecular motion of three highly conjugated solid-state molecular rotors 2–4 with alkyl groups were investigated by a combination of fluorescence spectroscopy, transmission electron microscopy (TEM), powder X-ray diffraction (PXRD), and variable-temperature solid-state ²H nuclear magnetic resonance (VT ²H ssNMR). Their long conjugation made them highly emissive in tetrahydrofuran solution (Φf = 0.41, 0.21, and 0.18, for rotors 2, 3 and 4, respectively), and the elongated aromatic cores favored π–π intermolecular interactions upon aggregation in hexane. The TEM micrographs and PXRD studies of the resulting bulk showed that shorter chains generated larger amorphous domains in 2, as compared to 3 and 4. The ²H ssNMR experiments showed fast intramolecular rotation of their central 1,4-diethynylphenylenes with the lowest activation energy to rotation for compound 2, Eₐ = 5.34 kcal/mol. This relationship between amorphous/crystalline domains and intramolecular motion has not been reported before, and it could guide the design of new solid-state molecular rotors.
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