Baowen Zhang

Highly efficient co-sensitization of nanocrystalline TiO2 electrodes with plural organic dyes

Through cooperative interactions, each of the three organic dyes utilized achieved improved sensitizing abilities on nanocrystalline TiO2 electrodes in co-sensitization over single-dye-sensitization, which led to a wide (400–700 nm) and highly efficient (exceeding 70%) photocurrent action spectrum in triple-dye-sensitization and an overall power conversion efficiency (η) of 6.5% (AM1.5, 80 mW cm−2), the highest η to date for dye-sensitized solar cells (DSSCs) based on the co-sensitization of plural organic dyes, fully demonstrating the potential of co-sensitization in DSSC applications.

Photophysical, electrochemical, and photoelectrochemical properties of new azulene-based dye molecules

Four new azulene-based dye molecules, 3-(azulen-1-yl)-2-cyanoacrylic acid (Azu-1), 3-(7-isopropyl-1,4-dimethylazulen-3-yl)-2-cyanoacrylic acid (Guai-1), 5-(azulen-1-yl)-2-cyanopenta-2,4-dienoic acid (Azu-2), and 5-(7-isopropyl-1,4-dimethylazulen-3-yl)-2-cyanopenta-2,4-dienoic acid (Guai-2), were synthesized and their photoelectrochemical properties were studied in dye-sensitized solar cells (DSSCs). All of them exhibit, in the visible region, a strong absorption band coming from the S0–S2 transition and a very weak band coming from the S0–S1 transition, and the transition assignments are supported by theoretical calculations using time-dependent density functional theory (TD-DFT) at the B3LYP/6–31G* level. In sensitization of nanocrystalline TiO2 electrodes, reducing their adsorption amount on the TiO2 surface (by co-adsorption with deoxycholic acid) mitigates dye aggregation and improves their photoelectric conversion efficiency greatly. Also, extending the conjugated side chain (Azu-2vs.Azu-1 or Guai-2vs.Guai-1) not only shifts their photoelectric response to longer wavelengths and therefore enhances the short-circuit photocurrent, but also increases the open-circuit photovoltage significantly. Moreover, it was found that the electron injection efficiencies varied remarkably with excitation wavelength, suggesting direct electron injection from the S2 state of these dye molecules.

Photoelectrochemical properties of TiO2 electrodes sensitized by porphyrin derivatives with different numbers of carboxyl groups

Abstract The photochemical and photoelectrochemical properties of two porphyrin derivatives with different numbers of carboxyl groups were investigated. The two porphyrin derivatives are 5-(4-carboxyphenyl)-10,15,20-tritolylporphyrin (H2TC1PP) and 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin (H2TC4PP). The interaction between the porphyrin and TiO2 is determined by the UV–vis spectra. Differences in adsorption behavior of the two porphyrin derivatives on the TiO2 electrode surface were observed. The IR data suggest that both of the porphyrins adsorb by bridging or bidentate chelate coordination on the TiO2 surface. Comparing the luminescence spectra of the two porphyrins in solution and the solid state, no spectral difference was observed. However, we found that the variation in the number of carboxyl groups has an influence on the fluorescence spectra of the adsorbed TiO2 electrode. Furthermore, we measured and compared the incident photon-to-current conversion efficiency (IPCE) and the light-to-electrical conversion efficiency of the porphyrin-sensitized solar cell. These results revealed that the number of functional groups influenced the photoelectrochemical properties of the cell.

Photooxidative degradation mechanism of model compounds of poly(p-phenylenevinylenes) (PPVs)

Abstract Seven model compounds of poly( p -phenylenevinylenes) [M-PPVs] were designed to perform the photooxidative degradation experiments. The degradation rates of M-PPVs depend on the nature, number, and position of substituents. The transient species including singlet oxygen, superoxide radical anion, M-PPV triplet state, M-PPV radical cation and anion in M-PPV photodegradation were observed and characterized systematically with ESR spin trapping, pulse radiolysis, and laser flash photolysis techniques. By using rose bengal, methylene blue, fullerene, tetraphenyl porphyrin, 9,10-dicyanoanthracene, or biacetyl as sensitizer in dye-sensitized M-PPV photodegradation experiments, we found that singlet oxygen does not play the principal role as previous reported. Results of triplet–triplet energy transfer from biacetyl to M-PPVs and M-PPV triplet state quenching by 1,4-diazabicyclo[2.2.2] octane (DABCO) suggested that the reaction between M-PPV triplet state and oxygen is really the key step in the processes of photodegradation of the conjugated structure.

Properties of a new pyrazoline derivative and its application in electroluminescence

As evaporated thin film and in solution, the absorption spectra, photoluminescence, electrochemistry and electroluminescence of the newly synthesized 1,3-diphenyl-5-pyren-2-yl-4,5-dihydro-1H-pyrazole (DPP) were investigated. The absorption spectra cover the whole near-ultraviolet region. At lower concentrations, the fluorescence emission is at 415 nm; at higher concentrations, a new face to face excimer emission appears on longer wavelengths; in the thin film state, the fluorescence emission becomes a single band peaking at 470 nm. Cyclic voltammetry of DPP and the hole transport material as evaporated thin films on ITO (indium tin oxide) was compared with that in solution and was used to determine the energy levels. The electric field strength dependent electroluminescent behavior of DPP was explained according to the energy levels by a tunneling mechanism, ruling out the possible cause by an excimer or exciplex formation. At a drive voltage of 18 V, the blue electroluminescence reached 2400 cd m –2 .

A new squaraine and Hg2+-based chemosensor with tunable measuring range for thiol-containing amino acids

A new squaraine, that undergoes absorption and fluorescence bleaching upon binding Hg2+, can serve as a turn-on colorimetric or fluorescent chemosensor for thiol-containing amino acids, presenting tunable measuring range by changing the concentration of Hg2+.

Mitochondria-targeting properties and photodynamic activities of porphyrin derivatives bearing cationic pendant

Four meso-tetraphenylporphyrin derivatives bearing either triphenylphosphonium ion-(P1 and P2) or triethylammonium ion-(P3 and P4) terminated alkoxy group at either para-(P1 and P3) or meta-(P2 and P4) position of one meso-phenyl group were designed and synthesized. P1-P4 show similar absorption and fluorescence emission spectra and (1)O(2) quantum yields. The more lipophilic nature of triphenylphosphonium ion over triethylammonium ion renders P1 and P2 higher octanol/water partition coefficients than P3 and P4. Confocal fluorescence microscopy proved that P1-P4 are all mitochondria-targeting. MTT assay showed that P1-P4 presented significant phototoxicity at the concentrations that dark toxicity is negligible towards human breast cancer cell line MCF-7 cells, displaying their application potential in PDT.

Greatly enhanced binding of a cationic porphyrin towards bovine serum albumin by cucurbit[8]uril

Binding affinity towards serum albumin and intracellular proteins is of importance for a photodynamic therapy (PDT) sensitizer to selectively localize in tumours and efficiently induce cell death. In this paper, it was found that cucurbit[8]uril (CB8) can greatly improve the binding affinity of 5,10,15,20-tetrakis(1-methyl-4-pyridinio)porphyrin tetra(p-toluenesulfonate) (TMPyP), a promising PDT photosensitizer, towards bovine serum albumin (BSA). Absorption, fluorescence emission, (1)H NMR, dynamic light scattering, atomic force microscope, as well as protein photocleavage measurements suggest that the binding enhancement originates from the formation of a ternary complex of CB8·TMPyP·tryptophan residues. This finding opens up a new approach for the development of more efficient PDT agents.

Synthesis of a water-soluble cyclodextrin modified hypocrellin and ESR study of its photodynamic therapy properties

A water-soluble cyclodextrin modified hypocrellin B (HBCD) was designed and synthesized. HBCD retained the phototherapeutic properties and exhibited much stronger photoinduced damage to calf thymus DNA (CT DNA) than hypocrellin B and mercaptoacetic acid substituted hypocrellin B (MAHB). The mechanism of electron transfer from CT DNA to the triplet state of HBCD was confirmed by steady-state electron spin resonance (ESR) and a time-resolved ESR study.

A novel n-type red luminescent material for organic light-emitting diodes

A novel red luminescent material N,N-bis{4-[2-(4-dicyanomethylene-6-methyl-4H-pyran-2-yl)ethylene]phenyl}aniline (BDCM) with two (4-dicyanomethylene)-4H-pyran electron-acceptor moieties and a triphenylamine electron-donor moiety for application in organic light-emitting diodes (OLEDs) was synthesized. The resultant compound has a sterically well-hindered structure and a high fluorescence yield. The photoluminescence (PL) of this compound in solution and solid film and the electroluminescence (EL) have been studied. Based on its intense sterically hindered structure, the pure BDCM film prepared shows a bright red PL emission. The three-layered EL device with the structure ITO/CuPc/DPPhP/BDCM/Mg:Ag has a turn-on voltage of less than 4 V, which suggests that BDCM has an excellent electron injection property. A bright luminance of 582 cd m−2 is obtained for the device at 19 V.