RESUMEN

Metal-organic frameworks (MOFs), an emerging class of highly ordered crystalline porous materials, possess structural tunability, high specific surface area, well-defined pores, and diverse pore environments and morphologies, making them suitable for various potential applications. Moreover, hydrogen-bonded organic frameworks (HOFs), constructed from organic molecules with complementary hydrogen-bonding patterns, are rapidly evolving into a novel category of porous materials due to their facile mild preparation conditions, solution processability, easy regeneration capability, and excellent biocompatibility. These distinctive advantages have garnered significant attention across diverse fields. Considering the inherent binding affinity between MOFs and HOFs along with the fact that many MOF linkers can serve as building blocks for constructing HOFs, their combination holds promise in creating functional materials with enhanced performance. This feature paper provides an introduction to the interconversion between MOFs and HOFs followed by highlighting the emerging applications of MOF-HOF composites. Finally, we briefly discuss the current challenges associated with future perspectives on MOF-HOF composites.

RESUMEN

A butterfly-shaped phenothiazine derivative, PTTCN, was synthesized to obtain pure organic porous crystals for the highly efficient absorptive separation of toluene (Tol) and methylcyclohexane (Mcy). Due to the presence of three polar cyano groups and nonplanar conformation, these molecules self-assembled into a hydrogen-bonded organic framework (X-HOF-5) with distinct cavities capable of accommodating Tol molecules through multiple hydrogen-bonding interactions. Upon solvent removal via heating, the activated X-HOF-5 retained its cavity structure albeit with altered stacking arrangements, accompanied by a remarkable fluorescent color change from cyan to green. X-HOF-5a can undergo a phase transformation into X-HOF-5 upon reabsorption of Tol, while exhibiting no accommodation of Mcy due to the weak intermolecular interaction between PTTCN and Mcy. This suggests that the activated HOF material prefers Tol over Mcy. Moreover, X-HOF-5a may selectively accommodate Tol in a Tol/Mcy equimolar mixture, and the purity of Tol can reach 97% after release from the framework. Additionally, it is noteworthy that the HOF material exhibits recyclability without any discernible loss in performance.

RESUMEN

Flexible crystals that can capture solar energy and convert it into mechanical energy are promising for a wide range of applications such as information storage and actuators, but obtaining them remains a challenge. Herein, an elastic crystal of a barbiturate derivative was found to be an excellent candidate, demonstrating plastic bending behavior under natural sunlight irradiation. 1 H NMR and high-resolution mass spectrum data of microcrystals before and after light irradiation demonstrated that light-induced [2+2] cycloaddition was the driving force for the photomechanical effects. Interestingly, the crystals retained elastic bending even after light irradiation. This is the first report of flexible crystals that can be driven by natural sunlight and that have both photomechanical properties and elasticity. Furthermore, regulation of the passive light output direction of the crystals and transport of objects by applying mechanical forces and light was demonstrated.

RESUMEN

A series of carbazole-based vinyl-benzoxazole derivatives have been synthesized in order to verify whether X-ray diffraction (XRD) simulation can give more information about intermolecular stacking in the gel phase. It was found that their gelation capabilities were strongly dependent on the length of the alkyl chain. The compounds with shorter alkyl chains have lower critical gelation concentrations (CGCs) in nonpolar alkane and alcohols with longer carbon chains. On the other hand, compounds with long alkyl chains presented small CGCs in polar methanol. Powder XRD structure solution gave more information about intermolecular stacking than the traditional way of analyzing diffraction peaks to derive approximate molecular stacking patterns. The results verified that gelators had a similar head-to-tail π-stacking between aromatic groups in gel phases although different slipping angles existed. Moreover, ordered stacking between the alkyl chains was also present.

RESUMEN

A linear distyrylanthracene derivative (DDATAn) with two diaminotriazine (DAT) groups acting as the hydrogen bond (H-bond) units was designed and synthesized in order to construct flexible organic porous crystals. H-bonds between the DAT moieties helped the molecules to construct a double interpenetrated two-dimensional layer, and the stacking between layers provided a H-bonded organic framework (X-HOF-3) with one-dimensional solvent channels. When X-HOF-3 was placed in contact with methanol, the fluorescent colors of the HOF exhibited an apparent bathochromic shift. More interestingly, the methanol-activated HOF was able to rapidly adsorb water from the air, which was accompanied by a change in fluorescent color from yellow to red. Under heating, water was released from the HOF and the fluorescent color returned to yellow. Water molecules in the pores were also able to be released after an applied mechanical force disrupted the ordered structure of the HOF. Based on these stimuli-responsive properties, these HOFs can be used as advanced functional materials in anticounterfeiting applications.

RESUMEN

A nonplanar phenothiazine derivative with three cyano moieties (PTTCN) is designed and synthesized to achieve functional crystals for absorptive separation of benzene and cyclohexane. PTTCN can crystallize into two kinds of crystals with different fluorescence colors in different solvent systems. The molecules in two crystals are in different stereo isomeric forms of nitrogen, quasi axial (ax), and quasi equatorial (eq). The crystals with blue fluorescence in ax form may selectively adsorb benzene by a single-crystal-to-single-crystal (SCSC) transformation, but separated benzene from a benzene/cyclohexane equimolar mixture with a low purity of 79.6%. Interestingly, PTTCN molecules with eq form and benzene co-assembled to construct a hydrogen-bonded framework (X-HOF-4) with S-type solvent channels and yellow-green fluorescence, and can release benzene to form nonporous guest-free crystal under heating. Such nonporous crystals strongly favor aromatic benzene over cyclohexane and may selectively reabsorb benzene from benzene/cyclohexane equimolar mixture to recover original framework, and the purity of benzene can reach ≈96.5% after release from framework. Moreover, reversible transformation between the nonporous crystals and the guest-containing crystals allows the material to be reused.

RESUMEN

A dumbbell-shaped compound (TPAD) with four 2,4-diaminotriazine moieties as H-bond units and a benzene ring as a bridge group was found to form hydrogen-bonded organic frameworks (HOFs) with strong cyan fluorescence. An energy acceptor, 6,6',6″,6‴-(((benzo[c][1,2,5]thiadiazole-4,7-diylbis-(4,1-phenylene))bis(azanetriyl))tetrakis(benzene-4,1-diyl))tetrakis(1,3,5-triazine-2,4-diamine) (BTAD), with the same molecular skeleton as TPAD and a longer emission wavelength could homogeneously distribute within the framework of TPAD through occupying the locations of TPAD. As a result, two-component HOFs (TC-HOFs) were formed. The nonradiative energy transfer from TPAD as the donor to BTAD as the acceptor happens within frameworks owing to the efficient spectral overlap between the emission of TPAD and the absorption of BTAD. Moreover, the emission wavelengths and colors of TC-HOFs could be easily and continuously modulated by the content of the acceptor. The fluorescence color changed from cyan to orange when the content of BTAD gradually increased. This finding affirms that TC-HOFs with continuously adjustable composition can be constructed from two molecules with the same molecular skeleton, and highly efficient nonradiative energy transfer may happen in porous TC-HOFs. To the best of our knowledge, these TC-HOFs are the first example of TC-HOFs involved in energy transfer.

RESUMEN

Guest molecules may endow porous materials with new or enhanced properties as well as functions. Here, a porous hydrogen-bonded organic framework (HOF) constructed from a three-armed triphenylamine derivative is used to investigate how guests regulate photoluminescence and trigger force-stimuli response. It was found that guest solvents in pores might regulate HOF's luminescence. Interestingly, acetic acid as a guest endowed HOF materials with longer emission wavelengths and triggered the responses to mechanical force stimuli. Under shear force, an obvious blueshift in emission spectra was observed because of the loss of free guests and the conversion of π-stacking model. Further blue-shifted emission appeared while the bound guests were completely removed by heating. Mechanofluorochromic HOF materials could be regenerated through recrystallization and adsorbing guest. Conversely, HOFs with other guests and activated HOFs only resulted in a slight change in their fluorescence behaviors after force stimuli.

RESUMEN

Generally, strong phosphorescence always implies a short luminescence lifetime. So, pure organic molecules with strong persistent phosphorescence at room temperature are rarely explored. Here, a new strategy is used to explore strong persistent phosphorescence of carbazole derivatives through an intermolecular moderate heavy atom effect. Flexible alkyl chains were inserted between the heavy atom and carbazole moieties so as to avoid a strong internal heavy atom affect. The results indicate that the photoluminescence properties of crystals strongly depend on molecular stacking in crystal states. Moreover, seven molecules among eight carbazole derivatives exhibit persistent room-temperature phosphorescence in their crystals and the ΦP values of three compounds exceed 9.5%. Notably, when a 6-(4-bromophenoxy)hexyl group is linked to carbazole, the ambient phosphorescent quantum yield reaches 39.5% and the lifetime is as long as 200 ms. Moreover, it emitted white light with a luminescent efficiency of 72.6% owing to the coexistence of strong fluorescence and phosphorescence.

RESUMEN

[This corrects the article DOI: 10.1039/C5SC03739E.].

RESUMEN

We have synthesized a series of new ß-iminoenolates and their corresponding difluoroboron complexes without any traditional gelation moieties, and some of them were able to gelatinize organic solvents. It was found that the presence of halogen atoms as substituents had a significant effect on gelation ability. In particular, bromo-containing compounds 4 A and 4 B exhibited excellent gelation abilities compared with other halogen-substituted gelators. By analyses of the single-crystal structure, the PXRD pattern of the xerogel, and electronic spectral changes during gelation, we deemed that π-π, C-H⋅⋅⋅F, and C-H⋅⋅⋅Br interactions were the driving forces for the gelation of 4 B. Interestingly, (Z)-1-(4-bromophenyl)-2-(3-methylpyrazin-2-yl)ethen-1-ol (8 A), prepared in this work, is the lowest-molecular-weight organogelator to have been reported. It should be noted that although ß-iminoenolates 3 A-5 A are nonemissive in solution, they emit strong yellow light in organogels, which suggests aggregation-induced emissive activity, whereas the difluoroboron complexes 3 B-5 B show strong fluorescence in solutions, organogels, and xerogel-based films. Moreover, we found that the emission of 4 B in a nanofiber-based film could be quenched significantly upon exposure to gaseous trifluoroacetic acid and that the decay time and detection limit were 0.5 s and 0.17 ppm, respectively. Thus, through this work we have provided a new strategy for the design of nontraditional π gelators by introducing halogen atoms into π-conjugated systems with moderate polarities.

RESUMEN

An L-phenylalanine derivative (C12PhBPCP) consisting of a strong emission fluorophore with benzoxazole and cyano groups is designed and synthesized to realize dual responses to volatile acid and organic amine vapors. The photophysical properties and self-assembly of the said derivative in the gel phase are also studied. C12PhBPCP can gelate organic solvents and self-assemble into 1 D nanofibers in the gels. UV/Vis absorption spectral results show H-aggregate formation during gelation, which indicates strong exciton coupling between fluorophores. Both wet gel and xerogel emit strong green fluorescence because the cyano group suppresses fluorescence quenching in the self-assemblies. Moreover, the xerogel film with strong green fluorescence can be used as a dual chemosensor for quantitative detection of volatile acid and organic amine vapors with fast response times and low detection limits owing to its large surface area and amplified fluorescence quenching. The detection limits are 796 ppt and 25 ppb for gaseous aniline and trifluoroacetic acid (TFA), respectively.

Asunto(s)

RESUMEN

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.

RESUMEN

Nanofibers based on phenanthroimidazole derivatives PCC, PDC, and PSC were fabricated by organogelation processes, and their fluorescence sensory properties towards acid were investigated. It was found that the emission of PCC in the nanofiber-based film could be quenched significantly upon exposure to gaseous TFA due to the formation of protonated PCC, in which ICT (intramolecular charge transfer) would occur. On the other hand, TFA vapor led to the emitting colors of PDC and PSC in the nanofiber-based films to turn to yellow and green from sky blue and blue, respectively. Additionally, we found that the decay times of PCC were 0.1 s and 1.9 s in probing the saturated vapor of TFA in nanofiber-based film and in spin-coated film, respectively. The results suggested that the high surface-to-volume ratio and large interspace in the nanofiber-based networks favored the enhanced adsorption, accumulation, and diffusion of gaseous molecules, resulting in such a high performance.

RESUMEN

A series of new triphenylamine functionalized ß-diketones 1­3 and their difluoroboron complexes 1B­3B were synthesized. They exhibited strong intramolecular charge transfer (ICT) emission. It was found that their self-assembling properties depended on the molecular structures. For example, compounds 1 and 1B, in which only one ß-diketone or difluoroboron ß-diketone unit was linked to triphenylamine, showed better gelation abilities directed by π­π interaction. Although bis-ß-diketone substituted triphenylamine 2 could not form organogels, its difluoroboron complex 2B could gel DMSO due to the strong dipole­dipole interactions. Compound 3 could form gels in polar solvents, while 3B formed gels in nonpolar solvents. Notably, the asymmetric gelators 1, 1B and 2B exhibited AIEE behaviors during the gelation. Although the emission of the symmetric compounds 3 and 3B decreased to a certain degree upon gelation, the obtained gels still gave strong emission. The gels formed from 1 and 3 emitted strong green light and those based on 1B­3B emitted strong orange or red light. These highly luminescent materials might have potential applications in emitting devices and fluorescent sensors.

Asunto(s)

RESUMEN

Two L-phenylalanine derivatives with 5,8-bis(2-(carbazol-3-yl)vinyl)quinoxaline (PCQ) and 5,8-bis[2-(carbazol-3-yl)]-2,3-dimethylquinoxaline (DCQ) as fluorophores were synthesized, and their photophysical properties were measured and compared. The two compounds were found to gelate some organic solvents and self-assemble into 1D nanofibers in gels. The wet gel of PCQ emitted a weak orange fluorescence, but the DCQ gel had a strong green one. This result can be due to the presence of two methyl groups and the nonplanar conformation of fluorophore in DCQ. The gel film of DCQ also showed significantly stronger fluorescence than that of PCQ. Thus, the wet gel and xerogel film of DCQ were selected to study their sensing properties to acids. The yellow wet gel of DCQ transformed into a brown sol upon the addition of 0.2 equiv trifluoroacetic acid (TFA), accompanied by emission quenching. The xerogel film of DCQ rapidly responded to volatile acids, such as TFA, HCl, and HOAc. The fluorescence of the xerogel film was gradually quenched with increased concentration of volatile acid vapors. The fibrous film exhibited low detection limits for volatile acid. The detection limits of the thin films for TFA, HCl, and HOAc reached 43, 122, and 950 ppb, respectively.

RESUMEN

An D-A-D gelator (DTCQ) was designed and synthesized using 2,3-dimethyl-5,8-di(thiophen-2-yl)quinoxaline and N-alkyl 3-aminocarbazole units as acceptor and donor, respectively, which were linked by a single bond. The compound could gelate several solvents, such as benzyl alcohol, aniline, acetophenone, and o-dichlorobenzene, as well as self-assemble into one-dimensional (1D) nanofibers in gel phase. The absorption and infrared spectra of the gels indicated that π-π interactions between aromatic moieties, intermolecular hydrogen bonds between amide units, and van der Waals forces were the driving forces for the formation of 1D self-assemblies and gel. DTCQ gel was red and emits red fluorescence because it has a strong absorption band at 487 nm and an emissive band at 620 nm. Moreover, DTCQ and a fullerene carboxylic acid formed two-component gel, in which the two compounds developed a hydrogen bond complex and self-assembled into 1D nanofibers with closely connected p- and n-channels. The nanofibrous xerogel film can rapidly generate a photocurrent under visible-light radiation through electron transfer from the gelator to fullerene, and then, the excellent exciton separation and charge transfer to two electrodes.

RESUMEN

A series of 4-nitrophenylacrylonitrile and phenylacrylonitrile derivatives consisting of a carbazole moiety was synthesized. Some of these derivatives with longer alkyl chains and a nitro group could gelatinize some organic solvents, such as ethanol, n-butanol, ethyl acetate, and DMSO. By contrast, phenylacrylonitrile derivatives did not form gels in measured solvents. This result proved that the electron-withdrawing nitro moiety was important for gel formation because it conferred the molecules with large dipole moments, which enhanced the intermolecular interaction. Analyses by UV-vis absorption, X-ray diffraction, and scanning electron microscopy showed that the gelator molecules could self-assemble into one-dimensional nanofibers with layer packing, which further twisted into thicker fibers and formed three-dimensional networks in the gel phase. The single crystal structure of C4CNPA implied that the gelators might adopt an anti-parallel molecular stacking because of their larger ground-state dipole moment. Interestingly, the organogels had enhanced fluorescence relative to solutions at the same concentrations.

RESUMEN

A linear coplanar carbazole-based benzoxazole derivative without any auxiliary moieties could gelatinize organic solvents, and exhibited emission enhancement owing to the J-aggregate formation.

RESUMEN

New indolocarbazole derivatives emitting strong blue light have been synthesized. It is found that the strong π­π interactions between indolocarbazoles 4­6 without long carbon chains lead to the formation of crystal or crystal-like aggregates. We have previously found that tert-butyl could tune the strength of π­π interactions between carbazole units and the organogels were obtained from tert-butyl substituted carbazoles directed by balanced π­π interactions. Herein, hexadecyl groups were introduced into N-positions of indolocarbazoles in order to reduce the strength of π­π interactions between indolocarbazoles, and compounds 7­9 were prepared. It is interesting that compounds 8 and 9 could form stable organogels in alcohols, acetone, DMSO, and so on, upon ultrasound stimulation. Combined with the results of electronic spectra, XRD patterns and the optimized molecular length based on the semiempirical (AM1) calculations, we suggested the molecular packing modes in gel states, in which the lamellar structures were involved. Although the fluorescence emission of indolocarbazoles 8 and 9 decreased during the gel formation to some extent, the obtained gel nanofibers still emitted strong blue light and the fluorescence emission of the film based on xerogel 9 decreased significantly upon exposure to gaseous TNT. It meant that the xerogels based on indolocarbazoles could be used as fluorescent sensors for detecting vapors of explosives.