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The existing asymmetric synthesis of enantiopure α-substituted cyclic ethers predominantly relies on the enantioselective C–C bond formation involving a prochiral oxocarbenium ion intermediate. In such a strategy, enantioselectivity and efficiency are typically susceptible to the electronic and substituent effects of either nucleophile or electrophile partners. Here, we describe a strategically different redox deracemization of α-substituted 1,3,4,9-tetrahydropyrano[3,4-b]indoles. This method exhibits good compatibility with the regional variation of the electronic or substituent effect of substrates, thus providing a practical and efficient supplement to the traditional strategy. [ABSTRACT FROM AUTHOR]

Rigid boomerang shaped triphenylamine functionalized bis-β-diketone-boron difluoride without alkyl chain and H-bonding unit exhibits good gelation ability in some mixed organic solvents directed by optimally balanced π–π interactions. [ABSTRACT FROM AUTHOR]

The first rigid dendritic gel with strong emission based on oligocarbazole was reported. It is interesting that the second generation of dendron exhibited gelation ability under ultrasound, and two-component gel could be formed from the first generation of dendron assisted by 1,6-diaminohexane. [ABSTRACT FROM AUTHOR]

Fluorine-free chalcones and chalcones bearing different numbers of fluorine atoms have been synthesized. It is found that fluorine can tune the reactivity of photo-induced [2 + 2] cycloaddition reactions in crystals. The higher the number of fluorine atoms, the higher the reactivity of the photodimerization. The single crystal structures and Hirshfeld surface analysis illustrated that the introduction of fluorine not only increased the molecular planarity but could also steer the potentially reactive double bonds in appropriate positions of the crystal lattices to meet Schmidt's criteria. Therefore, the stereospecific [2 + 2] cycloaddition reactions took place to afford one diastereoisomer from the reactive chalcones except for (E)-3-(4-fluorophenyl)-1-phenylprop-2-en-1-one (1FChH). Additionally, the chalcone-based molecular crystals exhibited various photomechanical behaviors, such as bending toward or away from the light source, swinging, cracking and jumping, driven by topo-photoreactions. As expected, the more efficient photo-induced [2 + 2] cycloaddition reactions in crystalline states led to more significant motions of the molecular crystals. Powder X-ray diffraction results suggested that the solid state [2 + 2] cycloaddition reactions changed the unit cell of the single crystals. The photo-induced bending toward or away from the light source for the needle-like crystals originated from the contraction or the expansion of the phototropic surface. Hence, the robust balancer fluorine in chalcones might play an important role in the crystalline packing. This provides a facile approach in crystal engineering to fabricate photo-induced mechanically responsive crystalline materials. [ABSTRACT FROM AUTHOR]

A Ni-catalyzed Suzuki-type cross-coupling of boronic acids with epoxides without an exogenous base and with broad substrate scope has been developed. The product selectivity of styrenyl epoxides is different from that of previous work. This methodology uses readily available starting materials to access a range of substituted alcohols, which are valuable feedstock chemicals. [ABSTRACT FROM AUTHOR]

Triphenylamine functionalized salicylaldimine difluoroboron complexes bearing different substituents have been synthesized. The photophysical results showed that these complexes exhibited intramolecular charge transfer (ICT) emission and solvatochromism. The fluorescence of these complexes could be well-tuned by the substituents in the ligands. The introduction of tert-butyl groups causes the complex TST to show obvious aggregation-induced emission (AIE) activity. In particular, the complexes without other substitutions or with the substitutions of bromo, tert-butyl and methoxyl on salicylaldimine moieties displayed reversible mechanofluorochromic (MFC) behaviors. XRD patterns and DSC curves of the complexes in different solid states suggested that the transformation between crystalline and amorphous states was responsible for the MFC properties. The relationship between the molecular structures and MFC properties suggested that the high polarity of the conjugated skeletons in difluoroboron complexes was beneficial for realizing high-contrast performance in mechanofluorochromism. [ABSTRACT FROM AUTHOR]

New D–π–A type phenothiazine-modified 2-hydroxychalcone analogues PTNn (n = 2, 4, 8, 12, and 16) have been synthesized, and they exhibited reversible mechanofluorochromism. Notably, the emission of PTNn in different solid-states was in the range of 600–800 nm, and red-emitting mechanofluorochromic (MFC) materials were seldom reported. The as-synthesized crystals of PTN16 emitted red light centered at 667 nm, and were changed into deep red emitting ground powders after grinding. The fluorescence emission could be recovered to the original state when the ground powders were fumed with the DCM vapor or heated. The MFC processes were accompanied by the transformation between crystalline and amorphous states, which could be confirmed based on the results of XRD patterns in different solid-states. Additionally, it was found that the length of the alkyl chain affected the performance in mechanofluorochromism for PTNn. The dye bearing a short carbon chain showed high-contrast MFC behavior compared with the one bearing a long carbon chain. Moreover, PTN12 and PTN16 bearing long carbon chains could self-assemble into organogels in a certain amount of organic solvents, and gelation-induced emission enhancement was observed during organogelation. [ABSTRACT FROM AUTHOR]

New D–π–A-type triphenylamine-containing benzimidazoles, benzoxazoles and benzothiazoles have been synthesized. It was found that the introduction of a cyano group in vinyl and methyl in triphenylamine was favorable for producing mechanofluorochromism of the fused heterocyclic derivatives. The single crystal X-ray diffraction data revealed that the intermolecular interactions of the H-bonding formed from the cyano group and the C–H…π interaction formed from the methyl group would rigidify the molecular conformations, leading to strong solid-state emission. Interestingly, the solid-state emission of the synthesized triphenylamine-containing fused heterocycles bearing cyano and/or methyl groups could be tuned by external mechanical forces on account of the transition between crystalline and amorphous states or between a highly ordered crystalline state and a less ordered state. [ABSTRACT FROM AUTHOR]

New carbazole modified salicylaldimine derivatives 1a–3a and their difluoroboron complexes 1b–3b were synthesized. It was found that 3a and 3b bearing both tert-butyl and trifluoromethyl could form stable gels in some organic solvents, while no gel could be formed from 1a–1b and 2a–2b without tert-butyl or trifluoromethyl, respectively. It suggested that both tert-butyl and trifluoromethyl played key roles in the gel formation because they could tune the solubility of the compounds and adjust the strength of intermolecular interactions. It should be noted that there is no traditional gelation moiety involved in gelators 3a and 3b. The main driving force for the gelation of such nontraditional π-gelators was π–π interaction. Meanwhile, aggregation-induced emission (AIE) was detected during the organogelation process of 3a, and the gel–sol transition took place upon adding F−. Interestingly, complexes 1b and 3b exhibited reversible piezofluorochromic (PFC) behaviors upon grinding/fuming, which originated from the transformation between crystalline and amorphous states. Herein, we provided a new strategy for designing new stimuli-responsive multifunctional soft materials. [ABSTRACT FROM AUTHOR]

4-(Carbazol-9-yl)benzaldehyde could emit yellow RTP, which could last for 3 s because of efficient intersystem crossing. Moreover, multicolor luminescent switches could be realized by simply applying a mechanical force stimulus. [ABSTRACT FROM AUTHOR]

Cyanostyrene-based D–π–A type conjugated compounds bearing triphenylamine units (G1, G1-N and G2) have been synthesized. By tuning the conjugated skeleton and the electron withdrawing ability of the acceptor, green, orange and red light emitters were achieved. It is interesting that although their emissions in solutions were weak, we observed strong emission in solid states. For example, the ΦF of the dendritic molecule G2 in powder reached 0.67, which was more than 20 times of that in THF. The single crystal X-ray diffraction data revealed that the intermolecular H-bonds of C–H…O, C–H…N and C–H…π led to the increased rigidity of the molecular skeleton, which would restrict the intramolecular rotation, yielding high ΦF in solid states. These AIE compounds may become candidates for emitting materials. [ABSTRACT FROM AUTHOR]

A hydrogen bonded complex could self-assemble into one-dimensional fibers in its gel phase. The fibrous film could be used as a sensor to detect and discriminate aromatic and aliphatic amines. [ABSTRACT FROM AUTHOR]