Search

Four new D-π-A-type difluoroboron β-carbonyl cyclic ketonate complexes that contain carbazole units ( TCCH, TCCP, CCH, and CCP) have been synthesized that exhibited reversible mechanofluorochromic (MFC) behaviors. Interestingly, TCCH and TCCP, which contained a tert-butyl carbazole group, exhibited high-contrast mechanofluorochromism compared with CCH and CCP, which just contained a carbazole group. For example, shifts of Δ δ=49 and 20 nm were detected during the mechanofluorochromism of TCCH and CCH, respectively. We found that tert-butyl carbazole derivatives existed as isolated molecules in the as-synthesized crystals, on account of the steric hindrance of the tert-butyl groups, and that J-aggregates were formed upon grinding. Transformation between the isolated and aggregated molecules, which was stimulated by mechanical force, led to clear changes in the emission properties. However, J-aggregates were formed in the as-synthesized crystals of carbazole derivatives, and grinding only weakened the strength of the π-π interactions, thereby resulting in low-contrast mechanofluorochromism. Therefore, this approach provides a useful strategy for the design of MFC dyes with high performance. [ABSTRACT FROM AUTHOR]

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]

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]

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]