Xuexin Cheng

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.

Host–Guest Interaction of Hoechst 34580 and Cucurbit[7]uril

To track nuclear dynamic processes by fluorescence imaging, nuclear stains should be highly fluorescent, resistant to photobleaching, and inert to nuclear processes. The nuclear stains of the Hoechst family, such as Hoechst 34580, show bright fluorescence only on groove binding to DNA, and therefore may interfere with visualization of nuclear dynamic processes induced by other stimuli. We study host-guest interactions between Hoechst 34580 and Cucurbit[7]uril (CB7) in aqueous solutions. The formation of CB7-Hoechst 34580 inclusion complexes with stoichiometry of 2:1 in water and 1:1 in phosphate-buffered saline (PBS) solution (pH 7.0) is confirmed by (1)H NMR, absorption spectra, fluorescence spectra, MALDI-TOF MS, and molecular modeling. Compared to Hoechst 34580, the inclusion complex exhibits redshifted absorption, intensified fluorescence, improved photostability, weakened DNA binding affinity, comparable ability to penetrate cell nuclei, and better nuclear-staining capability, and thus a new avenue for the application of cucurbituril in fluorescence imaging is opened.

A ferrocenyl pyridine-based Ru(II) arene complex capable of generating ·OH and 1O2 along with photoinduced ligand dissociation

Photoactivated chemotherapy (PACT) and photodynamic therapy (PDT) are two types of cancer treatment modalities that rely on photoinduced ligand dissociation and photosensitized or photocatalyzed reactive oxygen species (ROS) generation to realize anticancer activities with high selectivity, respectively. In this study, a novel Ru complex, [(p-cym)Ru(bpy)(py-Fc)]2+ (1), where p-cym = para-cymene, bpy = 2,2′-bipyridine, and py-Fc = 4-pyridyl ferrocene, was demonstrated to show dual activity from PACT and PDT. 1 has a long-wavelength absorption band extending to 600 nm and can generate both hydroxyl radicals (·OH) and singlet oxygen (1O2) along with photoinduced monodentate ligand dissociation. As a result, 1 displays DNA photocleavage activity as well as phototoxicity against human ovarian adenocarcinoma cells SKOV3 and human lung adenocarcinoma cells A549. The underlying mechanisms were discussed by comparing the photophysical, photochemical, and photobiological properties of 1 with that of [(p-cym)Ru(bpy)(py)]2+ (2, py = pyridine) and free py-Fc, providing guidelines for developing new photoactivated metallodrugs with multiple functions.

Self-Assembly of Anionic Porphyrins and Alkaline or Alkaline Earth Metal Ions Mediated by Cucurbit[7,8]uril

Nanoscaled coordination polymers based on biologically prevalent ions have potential applications in drug delivery and biomedical imaging. Herein, coordination polymer nanoparticles of anionic porphyrins, including meso-tetra(4-carboxyphenyl)-porphyrin (H2 TCPP(4-)) and meso-tetra(4-sulfonatophenyl)-porphyrin (H2 TPPS(4-)), and alkaline or alkaline earth metal cations, such as K(+) and Ca(2+), were constructed in aqueous solution in the presence of cucurbit[7]uril (CB7) or cucurbit[8]uril (CB8). UV/Vis absorption and fluorescence spectroscopy, dynamic light scattering (DLS), scanning electron spectroscopy (SEM), and atomic force microscopy (AFM) were applied to explore the assembly and particle formation of porphyrin anions and metal cations mediated by CBn. The particle size depends on the kinds of CBn and metal cations and their concentrations. The uptake of H2 TPPS(4-) particles by tumor cells (A549 cells) was found to be more efficient than H2 TPPS(4-) at 37 °C, showing the application potential of such assembled particles in biology and medicine.