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Abstract New D-π-A type quinoline derivatives (CbzVQ and TPAVQ) were synthesized via Knoevenagel condensation reactions. They exhibited reversible high-contrast mechanofluorochromic (MFC) behavior under grinding/fuming treatment. Taking CbzVQ as an example, its fluorescence could be switched from blue to greyish green by grinding the as-synthesized sample into ground powders, and the fluorescence emission was red-shifted from 449 nm (with shoulders at 475 nm and 520 nm) to 578 nm (with shoulders at ca. 450 nm and 500 nm). Such large shift of the maximal emission peak during MFC processes was rare reported. In addition, the casting films of CbzVQ and TPAVQ emitted blue and green light, respectively, which was turned to red rapidly induced by TFA (trifluoroacetic acid) vapor. Moreover, the emission could be recovered stimulated by TEA (triethylamine) vapor, so the quinoline derivatives exhibited reversible fluorescent sensory properties. TPAVQ showed better performance in the detection of TFA vapor than CbzVQ due to the strong electron-donating ability of triphenylamine compared with carbazole. The detection limit and the decay time of TPAVQ towards TFA vapor were 163 ppb and 0.22 s, respectively. Apparently, the D-π-A type quinoline derivatives are candidates as multi-stimuli responsive fluorescent materials. Graphical abstract Image 1 Highlights • New D-π-A type quinoline derivatives bearing carbazole and triphenylamine are synthesized. • Quinoline derivatives show reversible high-contrast mechanofluorochromism. • The shift of the maximal emission for CbzVQ reaches 129 nm during mechanofluorochromic processes. • The emitting color of quinoline derivatives is turn to red from blue or green rapidly stimulated by TFA vapor. [ABSTRACT FROM AUTHOR]

Abstract New carbazole-modified pyrazole derivatives were synthesized. It was found that tert -butylcarbazole derivatives of TCPDP , TCPHP , TCPPM and TCPPF exhibited reversible mechanofluorochromic (MFC) behavior under the treatment of grinding/fuming with CH 2 Cl 2. Particularly, the emission of the as-synthesized crystals of TCPDP was weak and emerged in the ultraviolet region, while the grinding led to significant red-shift of the emission to the visible-light region, accompanied with the significant fluorescence enhancement on account of the formation of J -aggregates. Thus, TCPDP showed intriguing fluorescence switching in visible-light region during MFC processes, which could be easily observed visually. Additionally, TCPDP , TCPHP , TCPPM and TCPPF could form stable organogels in some organic solvents. Notably, the solutions of TCPPM and TCPPF were almost non-emissive, but gelation-induced blue emission was achieved. Thus, the fluorescence could be also turned on due to the AIE (aggregation-induced emission) during the gel formation. Graphical abstract Image 1 Highlights • New carbazole-modified pyrazole derivatives were synthesized. • Tert -butylcarbazole derivatives showed reversible mechanofluorochromism and good gelation abilities. • High-contrast mechanofluorochromism of TCPDP was achieved via fluorescence switching in visible-light region. • Gelation-induced emission of TCPPM and TCPPF was detected. [ABSTRACT FROM AUTHOR]

Abstract 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 CH 2 Cl 2 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. Graphical abstract Image 1 Highlights • New β-diketone difluoroboron complexes with high solid fluorescence quantum yields were synthesized. • BPCVB without any traditional gelation group formed organogels. • The xerogel-based film of BPCVB with red emission could detect gaseous aniline selectively. • These NIR dyes showed MFC behavior. [ABSTRACT FROM AUTHOR]

New difluoroboron β-carbonyl cyclic ketonate complexes CnB (n = 2, 16), in which carbazole was linked to difluoroboron β-diketonate directly, and DCnB (n = 2, 16), where two terminal carbazole units were bridged by vinyl groups to link to difluoroboron β-diketonate core, were synthesized. They exhibited reversible mechanofluorochromic (MFC) behavior under grinding/fuming or heating treatment. Particularly, the emission of DC2B and DC16B emerged in the range of 650–850 nm in the solid-state. They gave red and rose-red luminescence in the as-synthesized crystals and in the ground powders, respectively, during MFC processes. Such MFC materials emitting NIR (near-infrared) light were seldom reported. In addition, compared with C2B , C16B showed high-contrast mechanofluorochromism because the long alkyl chain might decrease the strength of π-π interactions in the as-synthesized crystals, leading to the emission appeared at the high-energy region (483 nm). The disassembling of parts of π-aggregates and the improvement of the molecular planarity led to red-shift of the emission (509 nm) upon grinding. [ABSTRACT FROM AUTHOR]

Herein, three new fluorostyrylindazoles bearing one, three and five fluorine atoms (FPIZ , TFPIZ and PFPIZ) have been synthesized. Interestingly, the crystal of PFPIZ bent back away from the lighht source at the initial stage of 365 nm light irradiation, and then it showed phototropic bending when prolong the irradiation time without changing the irradiation direction. It was found that the photo-induced [2 + 2] cycloaddition could lead to the expansion and contraction of the unit cell in different directions, and in turn trigger the crystal to exhibit macroscopic mechanical moving. Meanwhile, the photochemical reaction was reasonable for the photochromism of the PFPIZ , which is helpful for the visual observation of the photomechanical effects. For instance, the fluorescence of the crystals of PFPIZ was changed from blue-purple to white under 365 nm irradiation. Besides, TFA (trifluoroacetic acid) could quench the emission of the synthesized fluorostyrylindazoles to different degree in solutions as well as in the films. The acidochromism of the styrylindazole derivatives was originated from the protonation of indazole by acid. The design of multi-stimuli response crystalline materials would be helpful for the fabrication of intelligent photoactuators and fluorescence sensors. [Display omitted] • The molecular crystals based on (E)-1-methyl-3-(2-(perfluorophenyl)vinyl)-1 H -indazole exhibited photomechanical effects. • Stereospecific photo-induced [2 + 2] cycloaddition underwent in the crystal of PFPIZ. • The fluorescence of the crystals of PFPIZ was changed from blue-purple to white on account of the photodimerization. • The films of fluorostyrylindazoles could probe gaseous trifluoroacetic acid rapidly and sensitively. [ABSTRACT FROM AUTHOR]

Four fluorescent low molecular weight gelators based on benzoxazole or benzothiazole functionalized pyrimidine were designed and synthesized. The ability of the target was tested, and all compounds could form stable supramolecular gels in an alcohol/water mixture and its fluorescence increased during gel formation. Photophysical spectra during gel formation, SEM, XRD, FT-IR study suggested that the self-assembly was driven by hydrogen bonding, van der Waals forces and weak π-π interaction. Interestingly, the gel collapsed after being illuminated by 365 nm UV light and 1H NMR of the gel before and after illumination proved that the [2 + 2]-cycloaddition between the double bond of pyrimidine was responsible for the light response. Furthermore, the fluorescent of xerogel film could be quenched by volatile acids while the fluorescent of the solution was enhanced after acid was added. The different phenomena were discussed. The nano-fiber assembled via gel formation could be used as fluorescent imaging material of latent fingerprints. [Display omitted] • Design and synthesis of novel uracil derivatives containing benzoxazole and benzothiazole. • Benzoxazole-modified uracil derivatives exhibit good gelation abilities and driving force of gel formation was investigated. • The gel could respond to light and acid. The response mechanism was studied. • The nano-materials assembled via gel formation could be used as fluorescent imaging material of latent fingerprints. [ABSTRACT FROM AUTHOR]

New D-π-A type aminostyrylquinoxaline derivatives ( QDMA1 , QDMA2 , QTPA1 and QTPA2 ) were synthesized via Knoevenagel condensation reactions. It was found that their ICT (intramolecular charge transfer) emission were red-shifted significantly with increasing the solvent polarities. Interestingly, compound QTPA2 bearing two terminal triphenylamine groups exhibited reversible mechanofluorochromism. The emission of the as-synthesized crystals of QTPA2 was located at 542 nm, and it was red-shifted to 592 nm upon grinding, so the emitting color was changed from yellow to carmine. Meanwhile, the emission could be recovered when the ground powders were fumed with DCM vapor. XRD patterns and DSC curves in different solid states demonstrated that the mechanofluorochromism was due to the transformation between the crystalline and amorphous states. In addition, the protonation of the synthesized aminostyrylquinoxalines by TFA could lead to the colors of the solutions to change into dark green from yellow, accompanied with the quenching of the emission. Furthermore, we also found that the emission of QTPA2 in the film could be quenched significantly and rapidly stimulated by TFA vapor, and the detection limit and the decay time were estimated to be 167 ppb and 0.47 s, respectively. Therefore, the aminostyrylquinoxaline derivatives could be used as sensory materials to detect acids in solutions and in the films by naked eyes. [ABSTRACT FROM AUTHOR]

New difluoroboron β-ketoiminate boron complexes bearing benzoxazole ( CBO ) and benzothiazole ( CBS ) have been synthesized. It was found that CBO was almost non-emissive in THF, and the emission could be intensified significantly when great amount of H 2 O was added, illustrating AIE (aggregation-induced emission) property. CBS could not show AIE property in THF/H 2 O system, but its emission in solid state was also strong. The single crystal structure of CBS suggested that π-π interactions and the hydrogen bonds of C(Ar)−F⋅⋅⋅H, C(Ar)−H⋅⋅⋅S and C(Ar)−H⋅⋅⋅Cl would suppress the rotation of single bonds, resulting into obvious emission enhancement. It is interesting that the as-synthesized crystals of CBO and CBS both emitted azure light, and the grinding made their emitting colors to change into cyan and green, which could be recovered under fuming with DCM or heating. The reversible mechanofluorochromism was due to the transformation between crystalline and amorphous states, which could be confirmed from the results of absorption spectra, XRD patterns and DSC curves in different solid states. Additionally, the high-contrast mechanofluorochromism of CBS compared with CBO might be originated from the loose packing in crystalline state and the better π-electron delocalization. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

New tert -butylcarbazole-based Schiff bases TPMP and TPMA , as well as the difluoroboron complex of salicylaldimine TPOB were synthesized. It was found that TPMP and TPMA without any traditional gelation group could form organogels in toluene and o -dichlorobenzene, etc., stimulated by ultrasound. It was suggested that the planar π-skeletons and the large steric effect of tert -butyl groups would lead to appropriate π-π interaction to induce the gel formation. Interestingly, the nanofibers formed from salicylaldimine derivative TPMP could emit strong yellowish green light under UV irradiation. It should be noted that the difluoroboron complex of TPOB with non-planar aromatic unit could not gelate the selected solvents on account of the weak π-π interaction. However, it showed reversible piezofluorochromism. The as-prepared crystal of TPOB emitted strong yellow light and could be transformed into the powders emitting orange red light after grinding, and the fluorescence could recover when the ground powders were heated. Such reversible changes of the emitting colors for TPOB by the treatment of grinding and heating was resulted from the transformation between crystalline and amorphous states. Herein, we provided the strategy for fabricating new nontraditional π-gels directed by appropriate π-π interaction and new piezofluorochromic dyes via the introduction of non-planar π-skeletons. [ABSTRACT FROM AUTHOR]

New difluoroboron β-diketonate complexes functionalized with tert -butyl carbazole and carbazole ( TCBM and CBM ) have been synthesized, and they give strong emission in solid states with the fluorescence quantum yields of 0.63 and 0.99, respectively. Reversible mechanofluorochromic behaviors of TCBM and CBM are realized upon the treatment of grinding/fuming with CH 2 Cl 2 . Interestingly, the emitting colors of the annealed samples gained from the ground powders of TCBM depend on the heating temperature, and change from orange to yellow, yellowish green, and green with increasing temperature. The X-ray diffraction patterns illustrate that the transformation processes from crystalline structure to partial destroyed crystalline structure, till to amorphous state lead to the multi-color solid-state luminescence during thermofluorochromism. We deduced that tert -butyl can lead to the incompact packing of luminophores, which is more sensitive to external stimuli, so that multi-color solid-state luminescence can be afforded during mechanofluorochromic and thermofluorochromic processes. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

New branched benzothiadiazole-cored conjugated oligomers with terminal carbazoles 1 and 2 have been synthesized. It was found that no obvious shifts of the maximal absorption bands for 1 and 2 were detected in the films compared with those in solutions, indicating weak π-π stacking occurred in the solid states on account of site isolation effect of the branched architectures. Hence, the synthesized oligomers could emit strong red light in the films. Notably, the emission of the films based on 1 and 2 could be quenched obviously upon exposed to gaseous TNT and DNT. The fluorescence quenching efficiency of the oligomer 2 -based film reached 91% when exposed to the saturated vapor of DNT for 3 min at 55 °C. The linear Stern–Volmer plot and the decrease of the fluorescence lifetime of 2 induced by DNT suggested the fluorescence sensing mechanism was due to the photo-induced electron transfer. [ABSTRACT FROM AUTHOR]

A benzoxazole derivative called BVDA was synthesized. BVDA exhibited an AIE effect although there was H-aggregated dimer in the crystal. According to the spectral results and crystal structure, the presence of excimer and the restriction of intramolecular rotation are responsible for the AIE phenomenon. Moreover, BVDA could respond to proton in solution and to volatile acid vapours in film. BVDA exhibited three colours because its binding sites to proton have different basicities. These binding sites can then be protonated in turn. These results indicate that AIE fluorophores with H-aggregated dimer is possible. Furthermore, these fluorophores can exhibit stimuli-responsive characteristics through the introduction of functional moieties. [ABSTRACT FROM AUTHOR]

Abstract: Three new donor-π-acceptor (D-π-A) metal-free organic dyes, in which dendritic triphenylamine acts as donor, and furan, thiophene and benzene as π-linkers, were synthesized, characterized and used for the application of dye sensitized solar cell (DSSC). Among the fabricated DSSCs, the device based on the furan as π-linker exhibited a short circuit current density of 14.56 mA cm−2, an open circuit photo voltage of 0.71 V and a fill factor of 0.59, implying a power conversion efficiency (η) of 6.10%. The devices sensitized by dyes with thiophene and benzene as π-linker possessed relative lower η, 5.92% and 4.97%, respectively. [Copyright &y& Elsevier]