Switchable Dual Circularly Polarized Luminescence in Through-Space Conjugated Chiral Foldamers.

Organic materials with switchable dual circularly polarized luminescence (CPL) are highly desired because they can not only directly radiate tunable circularly polarized light themselves but also induce CPL for guests by providing a chiral environment in self-assembled structures or serving as the hosts for energy transfer systems. However, most organic molecules only exhibit single CPL and it remains challenging to develop organic molecules with dual CPL. Herein, novel through-space conjugated chiral foldamers are constructed by attaching two biphenyl arms to the 9,10-positions of phenanthrene, and switchable dual CPL with opposite signs at different emission wavelengths are successfully realized in the foldamers containing high-polarizability substitutes (cyano, methylthiol and methylsulfonyl). The combined experimental and computational results demonstrate that the intramolecular through-space conjugation has significant contributions to stabilizing the folded conformations. Upon photoexcitation in high-polar solvents, strong interactions between the biphenyl arms substituted with cyano, methylthio or methylsulfonyl and the polar environment induce conformation transformation for the foldamers, resulting in two transformable secondary structures of opposite chirality, accounting for the dual CPL with opposite signs. These findings highlight the important influence of the secondary structures on the chiroptical property of the foldamers and pave a new avenue towards efficient and tunable dual CPL materials.

Achieving Multiple Quantum-Interfered States via Through-Space and Through-Bond Synergistic Effect in Foldamer-Based Single-Molecule Junctions.

The construction of multivalued logic circuits by multiple quantum-interfered states at the molecular level can make full use of molecular diversity and versatility, broadening the application of molecular electronics. Understanding charge transport through different conducting pathways and how they interact with each other in molecules with a secondary structure is an indispensable foundation to achieve this goal. Herein, we elucidate the synergistic effect from through-space and through-bond conducting pathways in foldamers derived from ortho-pentaphenylene by the separate modulation on these pathways. The shrinkage of central heterocycles' sizes allows foldamers to stack with larger overlap degrees, resulting in level-crossing and thus transformation from constructive quantum interference (CQI) to destructive quantum interference (DQI) in a through-space pathway. The alteration of central heterocycles' connection sites enhances through-bond conjugation, leading to amplified contribution from a through-bond pathway. The enhanced through-bond pathway destructively interferes with the through-space pathway, exerting a suppression effect on transmission. Therefore, four quantum-interfered states of through-space and through-bond combination are generated, including through-space CQI-dominated states, through-space DQI-dominated states, through-space CQI states with through-bond suppression, and through-space DQI states with through-bond suppression. These findings enable us to regulate charge transport within high-order structures via multiple conducting pathways and provide a proof of concept to construct multivalued logic circuits.

Anticancer Effects and Cell Death Pathways in Ultralow-Power 980 nm Laser-Triggered Photodynamic Therapy by Gd2O3:Yb, Tm Nanoparticles.

Upconverting Gd2O3:Yb, Tm nanoparticles that can provide photodynamic therapy (PDT) for cancer cells upon 980 nm near-infrared (NIR) laser irradiation are prepared. The nanoparticles emit bright blue upconversion fluorescence (470∼520 nm) when excited by a 980 nm laser. A well-selected PDT drug, merocyanine 540 (MC540), which shows an absorption maximum within the 495∼540 nm band, is loaded onto the surface of the nanoparticles to obtain Gd2O3:Yb, TmMC540. A prominent PDT-induced killing effect on both human cervical cancer cells (HeLa cells) and human hepatocellular liver carcinoma cells (HepG2 cells) is achieved under 980 nm laser irradiation at a very low power density of 0.65 W cm-2, which is lower than The American National Standard for the safe use of 980 nm lasers (0.72 W cm-2. The cell death modes are further studied in detail via a uranyl acetate section-staining method to analyze the morphological cell changes before and after PDT. With clear evidence of mitochondrial damage, chromatin condensation and the formation of apoptotic bodies, an apoptosis mechanism is confirmed to be responsible for both HeLa and HepG2 cell death in Gd2O3:Yb, Tm-MC540-mediated PDT. Due to excessive damage, the cancer cells are efficiently killed, and autophagy is found to be initiated immediately after PDT.

In vitro photodynamic therapy based on magnetic-luminescent Gd2O3:Yb,Er nanoparticles with bright three-photon up-conversion fluorescence under near-infrared light.

Yb(3+) and Er(3+) co-doped Gd2O3 nanoparticles were synthesized via a simple homogeneous precipitation method followed by subsequent heat treatment. Morphology characterization results showed that these nanoparticles were almost spherical in shape with diameters of 200-400 nm. The particles were further modified by polyethylene glycol (PEG) to improve their suspensibility in water. The sintering temperature was found to greatly influence the fluorescent properties of the products. After calcination at 700-1200 °C, the Gd2O3:Yb,Er nanoparticles could emit bright up-conversion fluorescence under 980 nm near-infrared (NIR) laser light excitation. The mechanism of up-conversion fluorescence was studied in detail and a three-photon process was observed for both green and red up-conversion fluorescence of the Gd2O3:Yb,Er nanoparticles. Different from many other Yb(3+),Er(3+) co-doped up-conversion materials, the prepared Gd2O3:Yb,Er nanoparticles emitted much stronger red light than green light. The reason was investigated and ascribed to the presence of abundant hydroxyl groups on the surface of the nanoparticles as a result of PEGylation. The nanoparticles could be taken up by the human cervical cancer (HeLa) cells and presented low toxicity. Well-selected photodynamic therapy (PDT) drugs, methylene blue (MB) with a UV/Vis absorption maximum (λmax) of 665 nm and 5-aminolevulinic acid (5ALA) which is a precursor of the natural photosensitizer photoporphyrin IX (PpIX) with a λmax of 635 nm, were loaded onto the nanoparticles respectively to obtain Gd2O3:Yb,Er-MB and Gd2O3:Yb,Er-5ALA nanoparticles. Being up-conversion nanoparticles (UCNPs), the taken up Gd2O3:Yb,Er nanoparticles exposed to 980 nm laser light emitted red fluorescence which activated the loaded MB and PpIX, and then killed the HeLa cells via a PDT mechanism. In vitro therapeutic investigation evidenced the prominent PDT effects of Gd2O3:Yb,Er-MB and Gd2O3:Yb,Er-5ALA upon NIR light irradiation. In magnetic resonance imaging (MRI) studies, the relaxivity values obtained for Gd2O3:Yb,Er were r1 = 2.2705 M(-1) s(-1) and r2 = 3.0675 M(-1) s(-1) with a r2/r1 ratio close to 1, suggesting that it would be a good candidate as a positive MRI agent. It is expected that these particles have applications in magnetic-fluorescent bimodal imaging and NIR light-triggered PDT.