Rational Design and Facile Synthesis of Dual-State Emission Fluorophores: Expanding Functionality for the Sensitive Detection of Nitroaromatic Compounds.

Six novel benzimidazole-based D-π-A compounds 4 a-4 f were concisely synthesized by attaching different donor/acceptor units to the skeleton of 1,3-bis(1H-benzimidazol-2-yl)benzene on its 5-position through an ethynyl link. Due to the twisted conformation and effective conjugation structure, these dual-state emission (DSE) molecules show intense and multifarious photoluminescence, and their fluorescence quantum yields in solution and solid state can be up to 96.16 and 69.82 %, respectively. Especially, for excellent photostability, obvious solvatofluorochromic and extraordinary wide range of solvent compatibility, DSE molecule 4 a is a multifunctional fluorescent probe for the visual detection of nitroaromatic compounds (NACs) with the limit of detection as low as 10-7 M. The quenching mechanism has been proved as the results of photoinduced electron transfer and fluorescence resonance energy transfer processes. Importantly, probe 4 a can sensitively detect NACs not only in real water samples, but also on 4 a-coated strips and 4 a@PBAT thin films.

Simple inorganic base promoted C-N and C-C formation: synthesis of benzo[4,5]imidazo[1,2-a]pyridines as functional AIEgens used for detecting picric acid.

Metal-free catalyzed intermolecular tandem Michael addition/cyclization has been developed for the synthesis of benzo[4,5]imidazo[1,2-a]pyridines from α-bromocinnamaldehyde and 2-substituted benzimidazoles. The reaction promoted by a simple inorganic base displays moderate to good yields and good functional group tolerance. The optical properties of some typical products have been investigated. We found that, due to the presence of the benzene ring at the C1-position of benzo[4,5]imidazo[1,2-a]pyridines which restricts intramolecular motion, as a new type of aggregation-induced emission (AIE) luminogen (AIEgen), they show very good solid-state fluorescence with quantum yields up to 88.80%. Importantly, the AIE performance of compound 3b can be useful to detect the nitroaromatic explosive picric acid (PA) with a detection limit and quenching constant of 42.5 nM and 7.27 × 104 M-M, respectively.

(E)-2-[2-(3-Fluoro-phen-yl)ethen-yl]quinolin-8-yl acetate.

In the crystal of the title compound, C(19)H(14)FNO(2), the mol-ecules are linked by C-H⋯O hydrogen bonds in translational chains along the b axis. The dihedral angles formed by the quinoline system with the fluoro-benzene ring and the acet-oxy group are 8.15 (3) and 77.42 (4)°, respectively.

Locking high energy 1D chain of dichloromethane molecules containing abnormally short Cl···Cl contacts of 2.524 Å inside organic crystals.

1D helical channels can be created by "sticky" end-mediated formation of 1D helical stacks composed of short cavity-containing helices and are able to host 1D chains of dichloromethane molecules containing extraordinarily short intermolecular Cl···Cl contacts of 2.524 Å in length that computationally destabilize the host-guest complex by 14.94 kcal mol(-1).

(2E)-2-[2-(4-Chloro-phen-yl)hydrazin-1-yl-idene]-4,4,4-trifluoro-3-oxobutanal.

The title compound, C(10)H(6)ClF(3)N(2)O(2), was synthesized by coupling 4-dimethyl-amino-1,1,1-trifluoro-but-3-en-2-one with 4-chloro-benzene-diazo-nium chloride. It crystallizes with two mol-ecules in the asymmetric unit, which form two similar centrosymmetric dimers via hydrogen bonds. Extensive electron delocalization and intra-molecular N-H⋯O hydrogen bonds are responsible for a planar conformation of the mol-ecules (maximum deviations = 0.010 and -0.015 Šfor the two molecules). In addition to hydrogen bonds, π-π stacking inter-actions with centroid-centroid distances of 3.604 (2) and 3.583 (2) Šcontribute to the stability of the crystal structure.

(E)-2-[2-(Penta-fluoro-phen-yl)ethen-yl]-8-quinolyl acetate.

The title compound, C(19)H(10)F(5)NO(2), was synthesized by the 1:1 condensation of 2-methyl-8-hydroxy-quinaldine with penta-fluoro-benzaldehyde. It crystallizes with two almost identical mol-ecules in the asymmetric unit. The penta-fluoro-benzene ring is essentially coplanar with the quinoline ring, forming dihedral angles of 2.49 (17) and 8.72 (16)° in the two mol-ecules.

(E)-2-[2-(2-Nitro-phen-yl)ethen-yl]-8-quinolyl acetate.

The title compound, C(19)H(14)N(2)O(4), crystallizes with two molecules with very similar conformations in the asymmetric unit; the angles between the two ring systems are 8.7 (1) and 4.2 (1)°. In the crystal, inter-molecular π-π inter-actions [centroid-centroid distance 3.973 (1) Å] lead to a three-dimensional network.