Baoxiang Gao

Pyrazine-Containing Acene-Type Molecular Ribbons with up to 16 Rectilinearly Arranged Fused Aromatic Rings

A series of acene-type conjugated molecules (1-5) containing 2-6 pyrazine units and up to 16 rectilinearly arranged fused aromatic rings were synthesized by condensation coupling of 1,2-diamines and 1,2-diketones. The energy gap of the molecules estimated from absorption edge decreases with an increase in molecular length, indicating the well-delocalized nature of the molecules. The cyclic voltammetry measurements suggest that the n-type properties of these ribbonlike pyrazine derivatives are dependent on the molecular length and the number of the pyrazine units. As the number of pyrazine units and the molecular length increase, the first reduction wave onset is shifted from -1.16 to -0.62 V (vs Ag/AgCl), corresponding to the LUMO energy levels of -3.24 and -3.78 eV, respectively. These molecules tend to aggregate in solution more readily with an increase in molecular length, as evident by (1)H NMR and UV-vis absorption spectra. Introduction of t-butyl groups in pyrene units can noticeably suppress the aggregation of these molecules in solution. High electron affinity, high environmental stability, and ease of structural modification make these compounds excellent candidates as a new class of n-type semiconductors.

Water-soluble and fluorescent dendritic perylene bisimides for live-cell imaging

We prepared dendritic perylene bisimide probes with triblock structures: perylene bisimides fluorescence cores, branched oligo(glutamic acid)s and polyethylene glycol chains. These probes showed good water solubility, low cytotoxicity and strong fluorescence in live cells.

Facile synthesis of self-host functional iridium dendrimers up to the fourth generation with N-phenylcarbazole-based polyether dendrons for non-doped phosphorescent organic light-emitting diodes

A facile synthesis has been demonstrated for the first time to construct self-host functional Ir-cored dendrimers up to the fourth generation on the basis of a newly developed polyether dendron, where the N-phenylcarbazole (NPC) moiety is used as the basic building block instead of benzene to improve charge transport whilst keeping the ease of preparation. With the growing generation number, the dendrimer size can be well tuned in a wide range of 4–10 nm. The obtained fourth generation dendrimer 45NPC-G4 is the largest Ir complex ever reported so far, having a diameter up to 10 nm and a molecular weight as high as 15.9 kDa. Most interestingly, the performance of non-doped phosphorescent organic light-emitting diodes (PhOLEDs) is found to be greatly dependent on the molecular size. For example, 9NPC-G2 (R ≈ 30 A) reveals the best luminous efficiency as high as 50.5 cd A−1 (56.6 lm W−1, 14.8%), whereas the efficiency of 45NPC-G4 (R ≈ 50 A) sharply drops to 10.5 cd A−1 (5.6 lm W−1, 3.4%). The results suggest that an appropriate size of 6 ± 2 nm is desirable to balance the dilemma between luminescence quenching and charge transport, and thereby realize highly efficient non-doped PhOLEDs.

Fluorescent water-soluble probes based on dendritic PEG substituted perylene bisimides: synthesis, photophysical properties, and live cell images

Water-soluble dyes based on dendritic polyethylene glycol (PEG)-substituted perylene bisimides were designed and synthesised. According to the distribution of hydrophilic dendritic PEGs, these dyes can be divided into two classes: (I) head–tail structured dyes, in which the hydrophobic perylene bisimides are the heads of the dyes and the hydrophilic dendritic PEG are used as the tails; (II) core–shell structured dyes, in which the hydrophobic perylene bisimides are encapsulated by the hydrophilic dendritic PEG. The aggregation behaviour and optical properties of these dyes were investigated. The two classes of water-soluble perylene bisimides show similar aggregation behaviour, optical and cytocompatibility properties. With increased dendron PEG generation, the aggregation of the PBI in an aqueous solution is completely suppressed by the hydrophilic bulky dendritic PEG groups, and the fluorescence quantum yield increases from 4% to 93%. These dendritic PEG-substituted perylene bisimides have good cytocompatibility. The head–tail structured dyes show a limited cellular uptake process. By contrast, the core–shell structured dyes are efficiently internalised by cells and accumulated in the cytoplasm.

Single molecular tuning of the charge balance in blue-emitting iridium dendrimers for efficient nondoped solution-processed phosphorescent OLEDs

The single molecular tuning of charge balance has been demonstrated here by integrating a p-type dendron, an n-type dendron and a blue emissive Ir core into one dendritic platform. Compared with the commonly used physical blending, not only can the charge balance be well tailored, but also the intrinsic phase separation can be successfully eliminated in such developed single molecular systems (B-TCz2TPO1 and B-TCz1TPO2). As a consequence, their corresponding nondoped solution-processed PhOLEDs achieve more than doubled external quantum efficiencies accompanied by a negligible efficiency roll-off.

Assembly–disassembly driven “off–on” fluorescent perylene bisimide probes for detecting and tracking of proteins in living cells

We have developed an assembly–disassembly driven “off–on” fluorescent bioprobe based on amphiphilic perylene bisimide. In aqueous solutions, the amphiphilic probes can form self-assembled nanostructures with quenched fluorescence. These probes could then be disassembled by the binding of the probes to the targeted proteins, and the disassembly process leads to a 23-fold enhancement in fluorescence intensity. Amphiphilic perylene bisimides could be used as probes for the detection and tracking of targeted proteins under live cell conditions.

Water-soluble dendritic polyaspartic porphyrins: potential photosensitizers for photodynamic therapy

We prepared these photosensitizers with two-block structures: porphyrin cores for singlet oxygen generation and branched dendritic polyaspartic as hydrophilic shells for inducing water solubility, thus reducing cytotoxicity and giving high singlet oxygen yields.

Core-Extended Terrylene Diimide on the Bay Region: Synthesis and Optical and Electrochemical Properties

Two novel core-extended terrylene diimides on the bay region (CETDIs) were synthesized via annulation of the four additional ethylene units or benzene units on the bay region of the terrylene diimide core. The optical and electrochemical properties of the two compounds were investigated. These CETDIs exhibited broad absorption spectra with high extinction coefficients, which span a wide range in the ultraviolet and visible spectrum from 300 to 700 nm. Furthermore, the redox process of the CETDIs increased from two waves to four waves, and the lowest unoccupied molecular orbital (LUMO) levels were enhanced from -4.00 to -3.59 eV.

Water-Soluble Fluorescent Probes Based on Dendronized Polyfluorenes for Cell Imaging

Novel water-soluble dendronized fluorescent polyfluorenes (DFPFs) are prepared from hydrophilic monomers and hydrophobic comonomers. Incomplete energy transfer is found to result in a two-color emission of the DFPFs at around 410 and 650 nm. The incomplete energy transfer can be attributed to the poor compatibility between the fluorene and benzothiadiazole units. Polyethylene oxide (PEO) encapsulation of the DFPFs shows over 90% cell viability, indicating good biocompatibility. These DFPFs show differential cellular uptake. P1 with fewer PEO chains exhibits limited cellular membrane uptake and low brightness in cells. By contrast, P3 with more PEO chains is efficiently internalized by cells and accumulated in the cytoplasm. A strong fluorescence from whole cells is also observed.

Amphiphilic dendritic peptides: Synthesis and behavior as an organogelator and liquid crystal

Summary New amphiphilic dendritic peptides on dendritic polyaspartic acid were designed and synthesized. The organogel and liquid crystal properties of these amphiphilic dendritic peptides were fully studied by field-emission SEM, temperature dependent FT-IR, differential scanning calorimetry, polarization optical microscopy and X-ray diffraction experiments. Amphiphilic dendritic peptides G3 show good organogel properties with a minimum gelation concentration as low as 1 wt %. Furthermore, amphiphilic dendritic peptides G3 can form a hexagonal columnar liquid crystal assembly over a wide temperature range.