Xerogel-based Film Research Articles

Supramolecular fluorescent organogel bearing 1,8-naphthalimide residue for the detection of Fe3+ through the gel-gel transformation

Supramolecular gels with metal ion-responsiveness are an important kind of smart materials due to their potential application in environmental monitoring. In this study, a novel l-glutamine-contained 1,8-naphthalimide derivative (NDG) has been designed and synthesized as an organogelator. NDG could self-assemble into stable supramolecular organogels in different kind of solvents, and the gelation process showed bright blue aggregation-induced emission (AIE). The self-assembly behavior, morphology and structure of NDG gels were thoroughly studied by various techniques. Interestingly, the obtained NDG organogel exhibited a fluorescence ‘‘turn-off’’ response for Fe3+ and formed a stable metallogel NDG-Fe3+. The detection limit (LOD) of NDG in diluted solution and gel states for Fe3+ was calculated to be 30.8 nM and 11.5 nM, respectively, indicating high sensitivity. In addition, the blue fluorescence emission of the gel system was restored in the presence of ascorbic acid and then quenched again with oxygen, which showed reversible fluorescence sensing effect and employed as a logic gate at the molecular level. Furthermore, xerogel-based film of NDG emitted strong blue emission and could be utilized as paper-based chemosensor to detect Fe3+. And also, the NDG gel had potential application in fluorescence display material.

Multi-stimuli-responsive fluorescent materials based on N, O-chelated BF2 complexes: Self-assembling, sensory properties and detection of latent fingerprint

Four new D-π-A type N,O-chelated BF2 complexes (TCBOB, TCBTB, TCQB and TCPB) were synthesized. It was found that TCPB bearing the ligand of N-(1-pyridinyl)benzoamide shows gelation ability in methylcyclohexane, DCM/peteroleum ether, etc. The time-dependent UV–vis absorption and fluorescent emission spectral changes during the gel formation revealed that π-π interactions play important roles in the self-assembling processes. Particularly, the emission of the xerogel-based film of TCPB can be quenched by TFA (trifluoroacetic acid) vapor, and it showed high performance in the detection of TFA compared with the spin-coating films of TCBOB, TCBTB and TCQB. In addition, the BF2 complexes exhibited reversible mechanofluorochromic behavior under the treatment of grinding/fuming or heating, and TCPB gave high-contrast mechanofluorochromism compared with others. XRD patterns in different solid states demonstrated that the external mechanical forces can induce the transformation from the crystalline to the amorphous states. Powder of TCPB was also used to image latent fingerprints on surface of glasses, and distinct fluorescent images were obtained.

β-Diketone difluoroboron complexes-based luminescent π-gelators and mechanofluorochromic dyes with low-lying excited states

New tert-butylcarbazole modified β-diketone difluoroboron complexes CVB, PCVB, MPCVB and BPCVB have been synthesized. It was found that BPCVB without any traditional gelation group formed organogel in toluene, xylene, 1,3,5-triethylbenzene and 1,4-dioxane. The gained organogel and xerogel based on BPCVB gave a strong red fluorescence. The emission for the xerogel-based film was quenched by aniline vapor selectively, and the detection limit was as low as 2.0 ppb. It is interesting that the solid emission of the synthesized complexes was in the range of 600–850 nm, and the highest solid fluorescent quantum yield reached 0.37. These NIR dyes showed MFC behavior. For example, the as-synthesized sample of PCVB gave an emission band at 647 nm, and emitted red light under UV irradiation. The grinding of the as-synthesized sample resulted in the emitting color to turn to dark purple, accompanied with the red-shift of the emission to ca. 700 nm. The emission could recover to initial states by fuming the ground powders with CH2Cl2 vapor. Based on the UV–vis spectra and XRD patterns in different solid-state for PCVB suggested that π-aggregates were formed in the as-synthesized crystals, and the grinding could destroy the aggregates and yield amorphous state. The transformation between crystalline and amorphous states led to MFC behavior.

Pyrimidine-containing β-iminoenolate difluoroboron complexes acting as non-traditional π-gelators and mechanofluorochromic dyes

A xerogel-based film based on a mechanofluorochromic dye of a β-iminoenolate difluoroboron complex could detect TFA vapor with high performance.

H- and J-aggregates formed from a nontraditional π-gelator depending on the solvent polarity for the detection of amine vapors.

A tert-butyl carbazole-modified difluoroboron β-diketonate complex (TCbzB) has been synthesized. Although no traditional gelation group was involved in TCbzB, it could form organogels in the mixed solvents of o-dichlorobenzene/cyclohexane (v/v = 1/5 or 1/2), toluene/cyclohexane (v/v = 1/2) and chlorobenzene/cyclohexane (v/v = 1/2). Interestingly, an orange organogel was obtained in o-dichlorobenzene/cyclohexane (v/v = 1/2) with relatively high polarity and red organogels were gained in the other three mixed solvents with relatively low polarity. TCbzB self-assembled into H-aggregates and J-aggregates in orange and red organogels, respectively, and the corresponding xerogels emitted yellow and red light, respectively, under UV illumination. The red emission of the xerogel-based film could be quenched significantly by gaseous n-propylamine and aniline because of the decomplexation of the difluoroboron β-diketonate complex by n-propylamine and the weak interactions between aniline and boron difluoride units.

Luminescent non-traditional π-gels fabricated from pyrimidine derivatives bearing carbazole for the detection of acid vapors

A series of new pyrimidine derivatives modified with carbazole (CM, CMH, CMCl and CMBr) and tert-butyl carbazole (TCM, TCMH, TCMCl and TCMBr) were synthesized. It was found that CM, CMCl, CMBr, TCM, TCMCl and TCMBr without traditional gelation groups could self-assemble into organogels with intense emission. It was found that V-shaped π-conjugated skeleton and π-π interactions were essential for the organogelation. It was interesting that the organogels could be destroyed by adding TFA (trifluoroacetic acid), accompanied with the quenching of the emission on account of the protonation of pyrimidine unit. In particular, the xerogel-based film of TCM emitting strong bluish green light could be used as fluorescent sensor to detect TFA vapor with the decay time and detection limit of 0.6 s and 95 ppb, respectively. Such high performance of the xerogel-based film in fluorescent responsive ability was originated from the high surface-to-volume ratios of nanomaterials and the large space in 3D networks, which were favorable for the adsorption and diffusion of the analytes. We provided new strategy for the design of non-traditional π-gelators and the fabrication of fluorescent sensory materials with high performance to detect gaseous analytes.

New non-traditional organogelator of β-diketone-boron difluoride complexes with terminal tetraphenylethene: Self-assembling and fluorescent sensory properties towards amines

New β-diketone-boron difluoride complexes functionalized with tetraphenylethene (TPEB, DTPEB and TTPEB) which exhibit AIE (aggregation-induced emission) properties have been synthesized. It was found that only boomerang-shaped DTPEB without any traditional gelation groups could form organogel in specific organic solvents. It gave strong orange red fluorescence in organogel as well as in xerogel-based film although it was non-emissive in solution. It is interesting that the emission of DTPEB in xerogel-based film could be quenched significantly upon exposure to triethylamine (TEA) vapour, and the detection limit was as low as ca. 0.1 ppb. This work provides a strategy for the synthesis of a new rigid non-traditional π-gelator via the construction of a boomerang-shaped π-conjugated skeleton. In addition, the gelation of the π-gelators with AIE ability is a facile method for the fabrication of luminescent organic nanomaterials.

Nontraditional π Gelators Based on β-Iminoenolate and Their Difluoroboron Complexes: Effect of Halogens on Gelation and Their Fluorescent Sensory Properties Towards Acids.

We have synthesized a series of new β-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 β-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.

Organogelation of cyanovinylcarbazole with terminal benzimidazole: AIE and response for gaseous acid

The intense emission of carbazole-modified benzimidazole in xerogel-based film can be quenched rapidly by gaseous acid due to protonation.

Structure–function relationships affecting the sensing mechanism of monolayer-protected cluster doped xerogel amperometric glucose biosensors

A systematic study of the structure–function relationships critical to understanding the sensing mechanism of 1st generation amperometric glucose biosensors with an embedded nanoparticle (NP) network is presented. Xerogel-based films featuring embedded glucose oxidase enzyme and doped with alkanethiolate-protected gold NPs, known as monolayer protected clusters (MPCs), exhibit significantly enhanced performance compared to analogous systems without NPs including higher sensitivity, faster response time, and extended linear/dynamic ranges. The proposed mechanism involves diffusion of the glucose to glucose oxidase within the xerogel, enzymatic reaction production of H2O2 with subsequent diffusion to the embedded network of MPCs where it is oxidized, an event immediately reported via fast electron transfer (ET) through the MPC system to the working electrode. Various aspects of the film construct and strategy are systematically probed using amperometry, voltammetry, and solid-state electronic conductivity measurements, including the effects of MPC peripheral chain length, MPC functionalization via place-exchange reaction, MPC core size, and the MPC density or concentration within the xerogel composite films. The collective results of these experiments support the proposed mechanism and identify interparticle spacing and the electronic communication through the MPC network is the most significant factor in the sensing scheme with the diffusional aspects of the mechanism that may be affected by film/MPC hydrophobicity and functionality (i.e., glucose and H2O2 diffusion) shown to be less substantial contributors to the overall enhanced performance. Understanding the structure–function relationships of effective sensing schemes allows for the employment of the strategy for future biosensor design toward clinically relevant targets.

Luminescent nanofibers fabricated from triphenylvinyl substituted carbazole derivatives via organogelation for sensing gaseous nitroaromatics

New triphenylvinyl substituted carbazole derivatives TPEICE, TPEC and TPECBr have been synthesized. They could self-assemble into nanofibers via organogelation processes in some organic solvents. Notably, the obtained xerogel-based films could emit strong fluorescence although the three compounds were non-emissive in solutions, indicating AIE in gel phases. The emission of TPEICE and TPEC in xerogel-based films could be quenched significantly upon exposed to gaseous DNT and TNT, while TPECBr could not sense nitro compounds on account of its poor electron donating ability. We also found that reversibility of the fluorescence response of TPEC was better than TPEICE because the photo-induced electron transfer would happen during the recognition of nitroaromatics for TPEICE and TPEC, except for the formation of charge–transfer complex between TPEICE and nitro compounds. Therefore, the different fluorescence response behaviors of TPEICE, TPEC and TPECBr towards nitroaromatics were resulted from their different electron donating abilities.