Reinforced Self-Assembly of Donor–Acceptor π‑Conjugated Molecules to DNA Templates by Dipole–Dipole Interactions Together with Complementary Hydrogen Bonding Interactions for Biomimetics

One of the most important criteria for the successful DNA-templated polymerization to generate fully synthetic biomimetic polymers is to design the complementary structural monomers, which assemble to the templates strongly and precisely before carrying polymerization. In this study, water-soluble, laterally thymine-substituted donor–acceptor π-conjugated molecules were designed and synthesized to self-assemble with complementary oligoadenines templates, dA₂₀ and dA₄₀, into stable and tubular assemblies through noncovalent interactions including π–π stacking, dipole–dipole interactions, and the complementary adenine-thymine (A-T) hydrogen-bonding. UV–vis, fluorescence, circular dichroism (CD), atomic force microscopy (AFM), and transmission electron microscopy (TEM) techniques were used to investigate the formation of highly robust nanofibrous structures. Our results have demonstrated for the first time that the dipole–dipole interactions are stronger and useful to reinforce the assembly of donor–acceptor π-conjugated molecules to DNA templates and the formation of the stable and robust supramolecular nanofibrous complexes together with the complementary hydrogen bonding interactions. This provides an initial step toward DNA-templated polymerization to create fully synthetic DNA-mimetic polymers for biotechnological applications. This study also presents an opportunity to precisely position donor–acceptor type molecules in a controlled manner and tailor-make advanced materials for various biotechnological applications

Highly Selective Two-Photon Fluorescent Probe for Ratiometric Sensing and Imaging Cysteine in Mitochondria

A novel ratiometric mitochondrial cysteine (Cys)-selective two-photon fluorescence probe has been developed on the basis of a merocyanine as the fluorophore and an acrylate moiety as the biothiol reaction site. The biocompatible and photostable acrylate-functionalized merocyanine probe shows not only a mitochondria-targeting property but also highly selective detection and monitoring of Cys over other biothiols such as homocysteine (Hcy) and glutathione (GSH) and hydrogen sulfide (H₂S) in live cells. In addition, this probe exhibits ratiometric fluorescence emission characteristics (<i>F</i>₅₁₈/<i>F</i>₄₅₂), which are linearly proportional to Cys concentrations in the range of 0.5–40 μM. More importantly, the probe and its released fluorophore, merocyanine, exhibit strong two-photon excited fluorescence (TPEF) with two-photon action cross-section (Φσ_max) of 65.2 GM at 740 nm and 72.6 GM at 760 nm in aqueous medium, respectively, which is highly desirable for high contrast and brightness ratiometric two-photon fluorescence imaging of the living samples. The probe has been successfully applied to ratiometrically image and detect mitochondrial Cys in live cells and intact tissues down to a depth of 150 μm by two-photon fluorescence microscopy. Thus, this ratiometric two-photon fluorescent probe is practically useful for an investigation of Cys in living biological systems

Fluorescence-Enhanced Chemosensor for Metal Cation Detection Based on Pyridine and Carbazole

A series of donor–acceptor systems incorporating a carbazole moiety as the donating unit and pyridine moiety as the accepting unit have been designed and synthesized. The spectroscopic and electrochemical behaviors of the carbazole derivatives demonstrate that the carbazole unit interacts with the electron-accepting group through the π-conjugated spacer, thus leading to the intramolecular charge transfer (ICT). The pyridine-substituted carbazole derivatives show significant sensing and coordinating properties toward a wide range of metal cations. Compound <b>S2</b> exhibits fluorescence enhancement upon association with transition metal cations, and compound <b>V3</b> shows high selectivity for Cu²⁺ among this series of materials. DFT calculations indicate the different association abilities of the dyes and the enhancement of ICT upon addition of the metal cations

A Zero Cross-Talk Ratiometric Two-Photon Probe for Imaging of Acid pH in Living Cells and Tissues and Early Detection of Tumor in Mouse Model

Acid–base disorders disrupt proper cellular functions, which are associated with diverse diseases. Development of highly sensitive pH probes being capable of detecting and monitoring the minor changes of pH environment in living systems is of considerable interest to diagnose disease as well as investigate biochemical processes in vivo. We report herein two novel high-resolution ratiometric two-photon (TP) fluorescent probes, namely, PSIOH and PSIBOH derived from carbazole–oxazolidine π-conjugated system for effective sensing and monitoring acid pH in a biological system. Remarkably, PSIOH exhibited the largest emission shift of ∼169 nm from 435 to 604 nm upon pH changing from basic to acidic with an ideal p<i>K</i>_a value of 6.6 within a linear pH variation range of 6.2–7.0, which is highly desirable for high-resolution tracking and imaging the minor fluctuation of pH in live cells and tissues. PSIOH also exhibits high pH sensitivity, excellent photostability, and reversibility as well as low cytotoxicity. More importantly, this probe was successfully applied to (i) sense and visualize the pH alteration in HeLa cells caused by various types of exogenous stimulation and (ii) detect and differentiate cancer and tumors in liver tissues and a mouse model, realizing its practical <i>in vitro</i> and <i>in vivo</i> applications

Novel Butterfly-Shaped Fused Heteroacenes: Synthesis, Properties, and Device Performance of Solution-Processed Field-Effect Transistors

Two tetrabrominated intermediates obtained by bromination of naphthodithiophene in different solvents were used to construct novel highly π-extended butterfly-shaped heteroarenes <b>1</b>–<b>6</b>, containing either an 8- or 10-fused ring. The solution-processed organic field-effect transistors based on compound <b>1</b> exhibited promising device performance with a hole mobility of 0.072 cm² V^–1 s^–1 and a current on/off ratio of 10⁶ under ambient atmosphere

Ratiometric Emission Fluorescent pH Probe for Imaging of Living Cells in Extreme Acidity

A novel ratiometric emission fluorescent probe, 1,1-dimethyl-2-[2-(quinolin-4-yl)­vinyl]-1<i>H</i>-benzo­[<i>e</i>]­indole (QVBI), is facilely synthesized via ethylene bridging of benzoindole and quinoline. The probe exhibits ratiometric fluorescence emission (<i>F</i>_522nm/<i>F</i>_630nm) characteristics with p<i>K</i>_a 3.27 and linear response to extreme-acidity range of 3.8–2.0. Also, its high fluorescence quantum yield (Φ = 0.89) and large Stokes shift (110 nm) are favorable. Moreover, QVBI possesses highly selective response to H⁺ over metal ions and some bioactive molecules, good photostability, and excellent reversibility. The probe has excellent cell membrane permeability and is further applied successfully to monitor pH fluctuations in live cells and imaging extreme acidity in Escherichia coli cells without influence of autofluorescence and native cellular species in biological systems

AIE-Active Fluorene Derivatives for Solution-Processable Nondoped Blue Organic Light-Emitting Devices (OLEDs)

A series of fluorene derivatives end-capped with diphenylamino and oxadiazolyl were synthesized, and their photophysical and electrochemical properties are reported. Aggregation-induced emission (AIE) effects were observed for the materials, and bipolar characteristics of the molecules are favored with measurement of carrier mobility and calculation of molecular orbitals using density functional theory (DFT). Using the fluorene derivatives as emitting-layer, nondoped organic light-emitting devices (OLEDs) have been fabricated by spin-coating in the configuration ITO/PEDOT:PSS­(35 nm)/PVK­(15 nm)/<b>PhN-OF­(</b><i><b>n</b></i><b>)-Oxa</b>(80 nm)/SPPO13­(30 nm)/Ca­(8 nm)/Al­(100 nm) (<i>n</i> = 2–4). The best device with <b>PhN-OF­(</b><b>2</b><b>)-Oxa</b> exhibits a maximum luminance of 14 747 cd/m², a maximum current efficiency of 4.61 cd/A, and an external quantum efficiency (EQE) of 3.09% in the blue region. Investigation of the correlation between structures and properties indicates that there is no intramolecular charge transfer (ICT) increase in these molecules with the increase of conjugation length. The device using material of the shortest conjugation length as emitting-layer gives the best electroluminescent (EL) performances in this series of oligofluorenes

Effective Theranostic Cyanine for Imaging of Amyloid Species in Vivo and Cognitive Improvements in Mouse Model

We report herein an investigation of carbazole-based cyanine, (<i>E</i>)-4-(2-(9-(2-(2-methoxyethoxy)­ethyl)-9<i>H</i>-carbazol-3-yl)-vinyl)-1-methyl-quinolin-1-iumiodide (SLM), as an effective theranostic agent for Alzheimer’s disease (AD). This cyanine exhibited desirable multifunctional and biological properties, including amyloid-β (Aβ)-oligomerization inhibition, blood–brain barrier permeability, low neurotoxicity, neuroprotective effect against Aβ-induced toxicities, high selectivity and strong binding interactions with Aβ peptide/species, good biostability, as well as strong fluorescence enhancement upon binding to Aβ species for diagnosis and therapy of AD. This cyanine has been successfully applied to perform near-infrared in vivo imaging of Aβ species in transgenic AD mouse model. The triple transgenic AD mice intraperitoneally treated with SLM showed significant recovery of cognitive deficits. Furthermore, those SLM-treated mice exhibited a substantial decrease in both of oligomeric Aβ contents and tau proteins in their brain, which was attributed to the induction of autophagic flux. These findings demonstrated for the first time that SLM is an effective theranostic agent with in vivo efficacy for diagnosis and treatment of AD in mouse models

Efficient Semisynthesis of (−)-Pseudoirroratin A from (−)-Flexicaulin A and Assessment of Their Antitumor Activities

Accumulating evidence indicates that natural <i>ent</i>-kaurane diterpenoids show great potential for medical treatment of different pathological conditions including cytotoxicity, antibacterial, and anti-inflammatory activity. Among a variety of diterpenoids tested, (−)-pseudoirroratin A displayed a promising antitumor property <i>in vitro</i> and <i>in vivo</i>. However, this diterpenoid could merely be isolated in a limited amount from a rare source of <i>Isodon pseudoirrorata</i>. To overcome such scanty source, we developed a novel, facile, and efficient semisynthetic strategy to prepare (−)-pseudoirroratin A from natural (−)-flexicaulin A, which can be expediently obtained from <i>I. flexicaulis</i> in a great quantity. The three-dimensional structure and the absolute configuration of our synthetic diterpenoid have been determined and confirmed with the X-ray crystallographic analysis. More importantly, we demonstrated for the first time that pseudoirroratin A exerted significant cytotoxicity against human colorectal carcinoma cells via an induction of apoptosis, as well as a remarkable suppression on tumor growth in a colon cancer xenograft mouse model

How to Optimize the Interface between Photosensitizers and TiO₂ Nanocrystals with Molecular Engineering to Enhance Performances of Dye-Sensitized Solar Cells?

In this work, the interfacial properties of a series of metal-free organic naphthodithienothiophene (<b>NDTT</b>)-based photosensitizers adsorbed on TiO₂ surfaces were investigated by a combination of ab initio calculations and experimental measurements. The calculations and experiments reveal that because of the efficient charge transfer from the adsorbed dyes to TiO₂ nanocrystal surface there is an upward shift for the energy levels of dyes and a downward shift for the conduction band of surface TiO₂ and that the band gaps for both of them are also reduced. Such electronic level alignments at the interface would lead to increased light absorption range by adsorbed dyes and increased driving force for charge injection but reduced open-circuit potential (<i>V</i>_oc). More interestingly, we found that molecule engineering of the donor group and introducing additional electron-withdrawing unit have little effect on the electronic level alignments at the interface (because band gaps of the dyes adsorbed on TiO₂ surfaces become approximately identical when compared with those of the dyes measured in solution) but that they can affect the steric effect and the charge separation at the interface to tune <i>V</i>_oc and the short-circuit current density (<i>J</i>_sc) effectively. All these findings suggest that optimizing the interfacial properties of dyes adsorbed on TiO₂ surfaces by synchronously modifying steric effects of dye molecules anchored on TiO₂ and charge-transfer and separation properties at the interfaces is important to construct efficient dye-sensitized solar cells