A fluorogenic dye activated by S-nitrosothiols.

Here we describe a coumarin-phosphine dye that undergoes activation of coumarin fluorescence upon reaction with S-nitrosothiols.

Room-temperature preparation of nanocrystalline TiO2 films and the influence of surface properties on dye-sensitized solar energy conversion.

An extremely easy method is presented for producing surfactant-free films of nanocrystalline TiO2 at room temperature with excellent mechanical stability when deposited on glass or plastic electrodes for dye-sensitized solar energy conversion. Prolonged magnetic stirring of commercial TiO2 nanoparticles (Degussa P25) in either ethanol or water results in highly homogeneous dispersions which are used to prepare TiO2 films with surface properties which depend on the solvent used for dispersing the particles, even after sintering. The optical and mechanical properties of films cast from ethanol and water dispersions are compared, and differences in the extent of surface defects and dye binding are observed. Optical absorption, photoluminescence, and resonance Raman spectra of TiO2 films sensitized with Ru(4,4'-dicarboxylic acid-2,2'-bipyridine)2(NCS)2 ("N3") reveal that the electronic coupling of the dye and semiconductor depends on the surface structure of the film which varies with film preparation. Current-voltage data for illuminated and dark dye-sensitized solar cells are obtained as a function of film preparation, and results are compared to spectroscopic data in order to interpret the microscopic basis for variations in solar cell performance, especially with regard to sintered versus unsintered TiO2 films. The results suggest that surface traps associated with oxygen vacancies play a critical role in determining the efficiency of dye-sensitized solar energy conversion through their influence on the binding and electronic coupling of the dye to the semiconductor.

Solvent effects on interfacial electron transfer from Ru(4,4'-dicarboxylic acid-2,2'-bipyridine)2(NCS)2 to nanoparticulate TiO2: spectroscopy and solar photoconversion.

Resonance Raman spectra are reported for Ru(4,4'-dicarboxylic acid-2,2'-bipyridine)2(NCS)2 (commonly called "N3") in ethanol solution and adsorbed on nanoparticulate colloidal TiO2 in ethanol (EtOH) and in acetonitrile (ACN), at wavelengths within the visible absorption band of the dye. Raman cross sections of free N3 in EtOH are found to be similar to those of N3 adsorbed on colloidal TiO2 in EtOH, and are generally lower than those of N3 on TiO2 in ACN. Strong electronic coupling mediated by surface states results in red-shifted absorption spectra and enhanced Raman signals for N3 adsorbed on nanocolloidal TiO2 in ACN compared to EtOH. In contrast, the absorption spectrum of N3 on nanocrystalline TiO2 in contact with solvent is similar for ACN and EtOH. Wavelength-dependent depolarization ratios for N3 Raman bands of both free and adsorbed N3 reveal resonance enhancement via two or more excited electronic states. Luminescence spectra of N3 adsorbed on nanocrystalline films of TiO2 and ZrO2 in contact with solvent reveal that the quantum yield of electron injection phi(ET) into TiO2 decreases in the order ACN > EtOH > DMSO. Dye-sensitized solar cells were fabricated with N3 adsorbed on nanocrystalline films of TiO2 in contact with ACN, EtOH, and DMSO solutions containing LiI/LiI3 electrolyte. Photoconversion efficiencies eta were found to be 2.6% in ACN, 1.3% in DMSO, and 0.84% in EtOH. Higher short circuit currents are found in cells using ACN, while the maximum voltage is found to be largest in DMSO. It is concluded that the increased photocurrent and quantum yield of interfacial electron transfer in acetonitrile as compared to ethanol and DMSO is primarily the result of faster electron injection of N3 when adsorbed on TiO2 in the presence of ACN as opposed to EtOH or DMSO.