Push-Pull Bisnaphthyridylamine Supramolecular Nanoparticles: Polarity-Induced Aggregation and Crystallization-Induced Emission Enhancement and Fluorescence Resonance Energy Transfer.

Emissive push-pull-type bisnaphthyridylamine derivatives (BNA-X: X=Me, Et, Bzl, Ph, BuBr, and BuTEMPO) aggregate in aqueous methanol. Furthermore, a two-step emission and aggregation process is controllable by varying the methanol-to-water ratio. At 2:3 MeOH/H2 O, crystallization-induced emission enhancement (CIEE) occurs via formation of an emissive crystal phase, whereas, at 1:9 MeOH/H2 O, aggregation-induced emission enhancement (AIEE) occurs, induced by emissive supramolecular nanoparticles (NPs). For BNA-Ph, the emission quantum yield was 25 times higher in aqueous methanol than that in pure methanol. Despite the high hydrophobicity of BNA-X (C log P=6.1-8.0), the spherical NPs were monodisperse (polydispersity indices <0.2). Moreover, the emissive NPs exhibited fluorescence resonance energy transfer (FRET) with pyrene; however, for BNA-X bearing the TEMPO radical (BNA-BuTEMPO), no FRET was observed because of quenching. In particular, the BNA-BuTEMPO NPs have a slow rotational correlation time (1.3 ns), suggesting applications as magnetic resonance imaging contrast agents with large relaxivity.

Selective synthesis of substituted amino-quinoline derivatives by C-H activation and fluorescence evaluation of their lipophilicity-responsive properties.

Push-pull type fluorescent amino-quinoline derivatives (TFMAQ) bearing phenyl aromatic groups in the 8-position (TFMAQ-8Ar series) were synthesized via palladium-catalyzed C-H activation reaction in short steps. The N-arylation or C-H activation reactions were selectively controlled with high yield by combinations of palladium and phosphine ligands. The TFMAQ-8Ar analogues exhibited fluorescent solvatochromism in non-polar and polar solvents. In non-polar solvent, the absolute fluorescence quantum yield was high, wheareas the fluorescence was almost quenched in polar solvent. The TFMAQ-8Ar derivatives also showed high fluorescence emission at solid state owing to the planar structure between the quinoline ring and phenyl ring at the 7-amino group, as demonstrated by X-ray crystal structure analysis. The fluorescence imaging of 3T3-L1 cell using TFMAQ-8Ar derivatives was performed by confocal laser microscopy. Strong and specific emissions at lipid droplets were observed owing to the accumulation of TFMAQ-8Ar derivatives. Therefore, we propose that the TFMAQ-8Ar derivatives should become a versatile fluorescence probe for the live imaging of lipid droplets.

Fluorescence Properties and Exciplex Formation of Emissive Naphthyridine Derivatives: Application as Sensors for Amines.

Water-soluble donor-acceptor-type fluorophore 15Nap-Cl having two trifluoromethyl groups and a Cl group on a 1,5-aminonaphthyridine framework was prepared. Fluorophore 15Nap-Cl showed strong solvatochromic fluorescence, and, as the solvent polarity increased, a bathochromic shift was observed accompanied by an increase in the fluorescence quantum yield. In addition, in the presence of amines such as ethylamine, diethylamine, and aniline, further considerable bathochromic shifts in the fluorescence were observed. Density functional calculations identified the source of the fluorescence behavior as exciplex formation between 15-Nap-Cl and the corresponding amine. The fluorescence behavior was exploited to fabricate a sensor that can identify various primary, secondary, and tertiary amines.

Photophysical Properties of Emissive Pyrido[3,2-c]carbazole Derivatives and Apoptosis Induction: Development towards Theranostic Agents in Response to Light Stimulus.

Pyridocarbazole moieties are present in many natural products, such as olivacine and ellipticine, and their derivatives are well-known anticancer agents. To develop functional therapeutic and diagnostic compounds, three emissive pyrido[3,2-c]carbazole derivatives, PC-X, containing secondary or tertiary amine groups, were synthesized from an aminoquinoline derivative using a palladium complex as the catalyst. X-ray diffraction analyses revealed that PC-X showed highly planar structures between the pyridine ring and the carbazole framework, exhibiting high fluorescence intensities along with solvatochromic behavior. Imaging of HeLa cells treated with PC-X showed no specific accumulation into the organelles; however, a comparative examination showed that the accumulation in mitochondria was the highest as compared to nuclei and lysosomes. Cytotoxicity analysis using HeLa cells showed that PC-H, containing a secondary amine group showed the highest cytotoxicity (IC50 ≈20 µm) as compared to another PC-X having a tertiary amine group. Colocalization with MitoTracker, a typical mitochondrial staining dye, showed apoptosis-like behavior with remarkable appearance of blebbing during irradiation with near UV light (403 nm), suggesting that the PC-H may not only behave as a fluorescence probe for the imaging organelles, but also as a therapeutic agent for inducing apoptosis in HeLa cells, thereby functioning as a theranostic agent.