Photovoltaic and spectral properties of tetraphenyloporphyrin and metallotetraphenyloporphyrin dyes

Influence of gamma ray irradiation and annealing temperature on the optical constants and spectral dispersion parameters of metal-free and zinc tetraphenylporphyrin thin films: A comparative study

In this work, we report on the effect of γ-ray irradiation and annealing temperature on the optical properties of metal-free tetraphenylporphyrin, H2TPP, and zinc tetraphenylporphyrin, ZnTPP, thin films. Thin films of H2TPP and ZnTPP were successfully prepared by the thermal evaporation technique. The optical properties of H2TPP and ZnTPP films were investigated using spectrophotometric measurements of the transmittance and reflectance at normal incidence of light in the wavelength range from 200 to 2500 nm. The absorption spectra of H2TPP showed four absorption bands, namely the Q, B, N and M bands. The effect of inserting Zn atom into the cavity of porphyrin macrocycle in ZnTPP molecule distorted the Q and B bands, reduced the width of absorption region and influenced the optical constants and dispersion parameters. In all conditions, the type of electron transition is indirect allowed transition. Anomalous dispersion is observed in the absorption region but normal dispersion occurs in the transparent region of spectra. We adopted multi-oscillator model and the single oscillator model to interpret the anomalous and normal dispersion, respectively. We have found that the annealing temperature has mostly the opposite effect of γ-ray irradiation on absorption and dispersion characteristics of these films.

Thermotropic Ionic Liquid Crystals

The last five years’ achievements in the synthesis and investigation of thermotropic ionic liquid crystals are reviewed. The present review describes the mesomorphic properties displayed by organic, as well as metal-containing ionic mesogens. In addition, a short overview on the ionic polymer and self-assembled liquid crystals is given. Potential and actual applications of ionic mesogens are also discussed.

Hybrid Junctions of Zinc(II) and Magnesium(II) Phthalocyanine with Wide-Band-Gap Semiconductor Nano-oxides: Spectroscopic and Photoelectrochemical Characterization

The optical properties of zinc phthalocyanine (ZnIIPc) and magnesium phthalocyanine (MgIIPc) in DMSO and DMF solutions have been extensively investigated, and the photoelectrochemical behaviors of layer-by-layer hybrid junctions formed of the two metallo(II) phthalocyanines (MIIPcs) and wide-band-gap colloidal semiconductors, namely, ZnO and TiO2 nanocrystals (NCs), have been probed. Different experimental conditions, such as the Pc center metal ion, dye concentration, and solvent identity, were investigated in order to elucidate their effects on the photoelectrochemical performances of the prepared heterojunctions. Finally, thermal treatment of either dye and NC films and control of the NC shape and surface chemistry were also studied and, interestingly, were found to be critical in affecting the performance of photochemical sensitization processes, occurring at the dye/oxide and oxide/solution interfaces.

Optical absorption of tetraphenylporphyrin thin films in UV-vis-NIR region

The optical absorption of thermally-evaporated tetraphenylporphyrin (TPP), in the UV-vis-NIR region has been studied. The absorption spectra recorded in the UV-vis region for the as-deposited and annealed films showed different absorption bands, namely the Soret, B, at region 360-490 nm, Q-band region consist of four bands in the region 500-720 nm and two other bands labeled N and M in UV region. The Soret band always shows splitting in all the TPP thin films and the effect of annealing on the intensities of these components have been observed. The spectra of the infrared absorption allow characterization of vibrational modes for the powder, as deposited and annealed thin films. Some of the optical absorption parameters, namely molar extinction coefficient (epsilon), half band width (Deltalambda), electronic dipole strength (q2), and oscillator strength (f), of the principal optical transitions have also been evaluated.

Time-resolved photocurrent generation in a photoelectrochemical cell with phthalocyanine

The kinetics of photocurrent generated in the photoelectrochemical cell (PEC) with phthalocyanine (Pc) dyes in the microsecond time scale was discussed. The shape of the kinetics is rather complex and it was discussed in terms of molecular phenomena and electrochemical processes occurring after laser flash illumination. Time constants were calculated from the photocurrent decay curves and at least three time components were well recognized (rise in 0.40 micros, declining in 0.40-0.45 micros and secondary increase in about 2 micros). The shape of the kinetics was discussed in terms of dye singlet and triplet state participation in photocurrent generation and also in terms of creation of the Helmholtz-Goy double layer at the dye layer-semiconductor interface. The alteration in shape of the Helmholtz-Goy double layer in photoelectrochemical cell after laser pulse was also discussed.