Crystal Structures, Thermal Properties, and Emission Behaviors of N,N-R-Phenyl-7-amino-2,4-trifluoromethylquinoline Derivatives: Supercooled Liquid-to-Crystal Transformation Induced by Mechanical Stimuli

Abstract

Phenyl-7-amino-2,4-trifluoromethylquinoline derivatives (R = Me (1), Et (2), isopropyl (3), and Ph (4)) were prepared as a new type of fluorophore responsive to external stimuli. 1, 2, 3, and 4 were obtained as single crystals including three crystal polymorphs (1α, 1β, and 1γ) of 1 and two (2α and 2β) of 2. In 4, a phase transition from 4 173 and 4 90 between 173 and 90 K was observed. The solid-state emission showed a red shift by 30−58 nm compared with the emission in n-hexane, and their emission properties depended on the molecular arrangements. The modes of molecular arrangements for 1α, 1β, and 1γ were a slipped parallel (SP), head-to-tail γ-type herringbone (HT-γ-HB), and head-to-head γ-type herringbone (HH-γ-HB); those for 2α and 2β were HT-γ-HB and head-to-tail dimer (HT-dimer), and that for 3 was head-to-tail columnar (HTC). 4 173 and 4 90 were similar HT-γ-HB. The crystal-to-crystal transformations from 1γ to 1β and from 2β to 2α were observed by heating and grinding the crystal, respectively, with emittance changes. After melting, on cooling, all crystals formed supercooled liquid (SCL) and then glass states. In the SCL state, molecules were amorphous and were quickly crystallized by a mechanical stimulus such as scratching. By taking advantage of the difference of emitting intensity between the SCL and the crystal states for 1, "writing" and "erasing" of a letter with scratching and heating, respectively, were demonstrated.

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

“…1 Since solid-state emission closely depends on molecular and crystal structures, the relationships between emission properties and crystal structures have been studied. 7 Similarly, the analogous 1,8-naphthyridine derivative IJ1,8Nap-NH 2 ) also having the arylamine skeleton in addition to an extra nitrogen atom compared to TFMAQ was expected to provide many crystal polymorphs. 3 They are known to show various crystal transformations between polymorphs.…”

Fluorescence Properties and Exciplex Formation of Emissive Naphthyridine Derivatives: Application as Sensors for Amines

“…Reduction of 2 with tin afforded 2‐chloro‐3,5‐diaminopyridine ( 3 ) as a white solid. Finally, by Combes synthesis in the presence of hexafluoroacetylacetone and montmorillonite K10 as catalyst, 15Nap‐Cl was obtained as a yellowish solid.…”

“…H 2 SO 4 , fuming HNO 3 , NaOH, POCl 3 Na 2 CO 3 , MgSO 4 , 35 % HCl solution, Sn powder, and hexafluoroacetylacetone were purchased from Nacalai Tesque Co. Ltd., Fujifilm Wako Pure Chemical Co. Ltd., Sigma‐Aldrich, or Tokyo Chemical Industry Co., Ltd. Compounds 1 and 2 were prepared according to the previously reported procedures . Silica gel for column chromatography was purchased from Kanto Chemical Ltd., Japan.…”

“…In general, amines ensors are based on ac hemical reactionb etween the fluorophore and the amine, and this interaction results in changes in fluorescence. [9,10] We have studied push-pull-type fluorophores consisting of aminoquinoline (TFMAQ) [11] or aminonaphthyridine (18Nap) derivatives, [12] which show fluorescencec hanges in response to variouse xternal stimuli such as solvent, [11] heat, [11][12][13] protons, [14] light, [15] scratching, [16] grinding, [17] and vapor. [18] Recently, tricyclic amidined erivatives DHIm and DHPy,i nw hich ad ihydroimidazoleo rd ihydropyrimidine ring is fused with the 18Nap framework, have been reported to exhibitf luorescence changes in response to ap roton source (Scheme 1).…”

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].…”