2,4-Trifluoromethylquinoline (TFMAQ) derivatives that have amine (1), methylamine (2), phenylamine (3), and dimethylamine (4) substituents at the 7-position of the quinoline ring were prepared and crystallized. Six crystals including the crystal polymorphs of 2 (crystal GB and YG) and 3 (crystal B and G) were obtained and characterized by X-ray crystallography. In solution, TFMAQ derivatives emitted relatively strong fluorescence (λf max=418-469 nm and φf(s)=0.23-0.60) depending on the solvent polarity. From Lippert-Mataga plots, δμ values in the range of 7.8-14 D were obtained. In the crystalline state, TFMAQ derivatives emitted at longer wavelengths (λfmax=464-530 nm) with lower intensity (φf(c)=0.01-0.28) than those in n-hexane solution. The polymorphous crystals of 2 and 3 emitted different colors: 2, λfmax=470 and 530 nm with φf(c)=0.04 and approximately 0.01 for crystal GB and YG, respectively; and 3, λ fmax=464 and 506 nm with φf(c)=0.28 and approximately 0.28 for crystal B and G, respectively. In both crystal polymorphs of 2 and 3, crystals GB and G showed emission color changes by heating/melting/cooling cycles that were representative. By following the color changes in heating at the temperature below the melting point with X-ray diffraction measurements and X-ray crystallography, the single-crystal-to- single-crystal transformations from crystal GB to YG for 2 and from crystal B to G for 3 were revealed.
All Science Journal Classification (ASJC) codes
- Organic Chemistry