Organic single crystals with elastic bending flexibility are rare because they are generally brittle. We report here fluorescent organic single crystals based on thiophene-tetrafluorobenzene-thiophene derivatives, mainly 1,4-bis(thien-2-yl)-2,3,5,6-tetrafluorobenzene. Three derivatives were synthesized by Pd-catalyzed cross-coupling reactions (Stille or direct arylation pathways). The crystallization of the derivatives gave large (mm- or cm-scale) crystals. Two crystals of 1,4-bis(thien-2-yl)-2,3,5,6-tetrafluorobenzene, 1, and 1,4-bis(4-methylthien-2-yl)-2,3,5,6-tetrafluorobenzene, 3, bent under applied stress and quickly recovered its original shape upon relaxation. The other crystal of 1,4-bis(5-methylthien-2-yl)-2,3,5,6-tetrafluorobenzene, 2, showed brittle breakage under applied stress (normal behavior). Fibril lamella crystal structure based on criss-cross packed slip-stacked molecular wires and its structural integrity are important factors for the design and production of next generation crystal materials with elastic bending flexibility. Furthermore, mechanical bending–relaxation resulted in reversible change of the morphology and fluorescence (mechanofluorochromism). Such bendable crystals would lead to the next generation solid-state fluorescent and/or semiconducting materials.
2-Arylquinolines 1 were obtained in good yields by reacting iodine or NIS with 2-aminochalcones 2, which were easily synthesized by the Claisen–Schmidt reaction from 2-nitrobenzaldehyde and acetophenones. The reaction of iodine with 2-isopropenylacetanilide (3a), followed by the addition of aq. NaHCO3, afforded 4-iodomethyl-2,4-dimethyl-4H-3,1-benzoxazine (6a), of which the structure has previously been reported to be 1-acetyl-2-iodomethyl-2-methyl-1,2-dihydrobenzazete (4a) or 1-acetyl-3-iodo-3-methylindoline (5a). The reaction mechanism is discussed.
Structural analysis of CO2-silicalite-1 crystals using the single-crystal X-ray diffraction method reveals that the crystal system is twinned monoclinic. The structure of silicalite-1 (MFI-type zeolites) loaded with CO2 has previously been solved in orthorhombic system [1], but the R value is still large. Since CO2 molecules are too small to maintain the orthorhombic structure, it is considered that the CO2-silicalite-1 crystals should be in the relaxed monoclinic twin phase. The diffraction data in the previous report is recalculated in P21
/n as the monoclinic twinning.
The location of physisorbed CO2 molecules on silicalite-1 zeolite (MFI-type) is determined using a single-crystal X-ray method. There are four sorption sites for CO2 molecules in the three-dimensional channel system of the silicalite-1. Two of them are in the straight channel in disorder (STR1 and STR2), while the other sites are in the sinusoidal channel (SIN) and at the intersection (INT). Their occupancy factors indicate that a large portion of the CO2 molecules are located in the straight channel. It is also revealed that the straight channel is the most favorable for CO2 molecules as sorption sites.
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