Lu Zhai

Nanofibers generated from nonclassical organogelators based on difluoroboron β-diketonate complexes to detect aliphatic primary amine vapors

New D–A–D type difluoroboron β-diketonate complexes with terminal triphenylamines ABA, ABVA and AVBVA were synthesized. It was found that stable organogels could be gained from ABVA and AVBVA without traditional gelation groups in mixed solvents containing 1,4-dioxane, and balanced π–π interactions were the driving forces for the gel formation. Interestingly, the organogels based on ABVA and AVBVA exhibited emission close to the NIR (near infrared) region. To the best of our knowledge, such narrow band gap low molecular-weight π-gelators have not been reported. In particular, xerogel-based films generated from ABVA and AVBVA could be used as sensors to detect gaseous aliphatic primary amines with high performance. For example, after exposing to saturated n-butylamine and n-propylamine vapors for 30 s, the emission of the films was quenched completely and new strong emission at ca. 560 nm appeared on account of the decomposition of the difluoroboron β-diketonate complexes.

Carbazole modified salicylaldimines and their difluoroboron complexes: effect of the tert-butyl and trifluoromethyl terminal groups on organogelation and piezofluorochromism

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.

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

New pyrimidine-containing β-iminoenolates and their difluoroboron complexes were synthesized. It was found that the ligand and the complex bearing tert-butyl could self-assemble into organogels in methylcyclohexane/1,4-dioxane and other solvents, but no organogel could be formed from the carbazole derivatives. This suggested that tert-butyl played a key role in the gel formation. It should be noted that no traditional gelation moiety was involved in the fully conjugated TCPPA ((Z)-2-(6-chloropyrimidin-4-yl)-1-(4-(3,6-di-tert-butyl-9H-carbazol-9-yl)phenyl)et-hen-1-ol) and TCPPAB (6-chloro-3-(4-(3,6-di-tert-butyl-9H-carbazol-9-yl)phenyl)-1,1-diflu-oro-1H-1l4,9l4-pyrimido[1,6-c][1,3,2]oxazaborinine), and π–π interactions were found to be the main driving forces for the gelation. Moreover, the xerogel-based film of TCPPAB emitting strong yellow light could be used as a “turn-off” fluorescent sensor to detect TFA vapor with the decay time and detection limit of 0.8 s and 260 ppb, respectively. On the other hand, the β-iminoenolate difluoroboron complexes exhibited reversible mechanofluorochromic behavior. The as-synthesized crystals of TCPPAB emitted strong green light and could be transformed into powders emitting orange light upon grinding, and the fluorescence could be recovered when the ground powders were fumed with CH2Cl2. Such reversible MFC processes for TCPPAB were suggested to have resulted from the transformation between crystalline and amorphous states. Herein, we provide a strategy for designing new multi-stimuli-responsive soft materials.