Crystal Structures and Emitting Properties of Trifluoromethylaminoquinoline Derivatives: Thermal Single‐Crystal‐to‐Single‐Crystal Transformation of Polymorphic Crystals That Emit Different Colors

Abstract

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 (lambda(max)(f)=418-469 nm and Φ(f)(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 (lambda(max)(f)=464-530 nm) with lower intensity (Φ(f)(c)=0.01-0.28) than those in n-hexane solution. The polymorphous crystals of 2 and 3 emitted different colors: 2, lambda(max)(f)=470 and 530 nm with Φ(f)(c)=0.04 and approximately 0.01 for crystal GB and YG, respectively; and 3, lambda(max)(f)=464 and 506 nm with Φ(f)(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.

Crystalline transformations of dinaphthyridinylamine derivatives with alteration of solid-state emission in response to external stimuli

“…have been investigated as functional molecules in the field of materials science. The crystal polymorphs of TFMAQ derivatives exhibited thermal single-crystalto-single-crystal (SC-to-SC) transformation 6 and supercooledliquid (SCL)-to-SC transformation by a mechanical stimulus with alteration of the emission color. 2 Crystal polymorphs, being the same molecule with different crystal structures, have been studied with the aim of avoiding alterations of the solubilities, bioavailabilities and stabilities in the pharmaceutical, food and cosmetic fields.…”

Effect of Hydrophobicity on the Self-Assembly Behavior of Urea Benzene Derivatives in Aqueous Solution

“…This is accompanied by a lower critical solution temperature (LCST) behavior, resulting in a turbid solution. In addition, UBD have been used in our laboratory for the development of functional materials; namely, radical nanoparticles have been employed for metal-free magnetic resonance imaging contrast agents [13], and push-pull-type, aminoquinoline-based fluorescent probes have been constructed for bioimaging applications [14][15][16][17][18]. Among the latter, we have successfully developed a tumor-imaging probe activated by heat treatment [19].…”

Molecular‐Level Understanding of Structural Changes of Organic Crystals Induced by Macroscopic Mechanical Stimulation

“…Single‐crystal X‐ray diffraction (XRD) analysis is the most powerful technique to elucidate crystal structure changes. When the crystals both before and after a structure change have sufficient integrity for single‐crystal XRD analyses, submolecular level information can be obtained . However, mechanical operations like grinding generally cause perturbation of crystal structures; most organic crystals are crushed to form a powder of the crystal or an amorphous material.…”