X-ray photoelectron spectroscopic investigation of phenosafranine adsorbed onto micro and mesoporous materials

The phenosafranine adsorbed onto the micro and mesoporous materials prepared by ion exchange method and interaction of the dye with host materials were studied by X-ray photoelectron spectroscopy to elucidate the influence of the host matrix on the binding energy of N 1s orbital. Core level N 1s X-ray photoelectron spectroscopy reveals the interaction between the dye and the solid surface through the hydrogen bonding between the hydrogen atoms of primary amino groups in dye molecule and the oxygen atom of surface hydroxyl groups. The strength of the hydrogen bonding depends on the nature of the solid surface. In the dye adsorbed onto the micro and mesoporous materials the interaction between adsorbed phenosafranine and the surfaces of the porous materials are found to modify the optical spectra and the excited state dynamics of the confined phenosafranine molecules. The change in photophysical properties of phenosafranine adsorbed on to the host materials on dehydration at elevated temperatures is attributed to the modification of host surface during dehydration process

Probing Flexibility in Porphyrin-Based Molecular Wires Using Double Electron Electron Resonance

A series of butadiyne-linked zinc porphyrin oligomers, with one, two, three, and four porphyrin units and lengths of up to 75 angstrom, have been spin-labeled at both ends with stable nitroxide TEMPO radicals. The pulsed EPR technique of double electron electron resonance (DEER) was used to probe the distribution of intramolecular end-to-end distances, under a range of conditions. DEER measurements were carried out at 50 K in two types of dilute solution glasses: deutero-toluene (with 10% deutero-pyridine) and deutero-o-terphenyl (with 5% 4-benzyl pyridine). The complexes of the porphyrin oligomers with monodentate ligands (pyridine or 4-benzyl pyridine) principally adopt linear conformations. Nonlinear conformations are less populated in the lower glass-transition temperature solvent. When the oligomers bind star-shaped multidentate ligands, they are forced to bend into nonlinear geometries, and the experimental end-to-end distances for these complexes match those from molecular mechanics calculations. Our results show that porphyrin-based molecular wires are shape-persistent, and yet that their shapes can deformed by binding to multivalent ligands. Self-assembled ladder-shaped 2:2 complexes were also investigated to illustrate the scope of DEER measurements for providing structural information on synthetic noncovalent nanostructures

Spectral and electrochemical studies of methylene blue and thionine encapsulated in zeolite-Y

Investigation on the spectral and electrochemical properties of methylene blue and thionine encapsulated in zeolite-Y is carried out. Both the dyes exist as monomer and H-aggregates in zeolites and the ratios for the aggregates of the dyes are different at the zeolite surface even though the dyes have similar basic structure. The electrochemical behaviour of thionine and methylene blue at zeolite modified electrode shows that both the dyes experience different environment at zeolite modified electrode and the presence of methyl groups in methylene blue plays a vital role in stabilizing the electroactive species at the electrode surface. The concentration of the supporting electrolyte is found to influence the nature of the redox process

Redox properties of phenosafranine at zeolite-modified electrodes-effect of surface modification and solution pH

Redox properties of cationic dye phenosafranine (3,7-diamino-5-phenylphenazenium chloride) (PS+) were studied at zeolite-modified electrodes using Zeolite-Y and NaZSM-5. The peak current and peak potential of phenosafranine-adsorbed zeolite were found to be influenced by the pH of the electrolyte solution. Observation of a second redox couple is suggested to be due to formation of new species at low concentration from the reduced phenosafranine at the zeolite-modified electrodes. Titanium dioxide nanoparticles encapsulated in the cavities of the zeolite or anchored on the external surface of the zeolite do not seem to affect the redox properties of adsorbed PS+. When the cyclic voltammograms are recorded immediately after the electrode is immersed into the solution, the redox potential of PS+ is found to be sensitive to the nature of the zeolite surface. The peak potential shifts towards positive region under continuous cycles as the surface hydroxyl groups get protonated in acidic electrolyte solution thereby forcing the movement of dye molecules from the zeolite surface to the zeolite electrode solution interface. The electron transfer rate constants for the adsorbed dye at the electrode are calculated to be 2.5 ± 0.2 s-1 and 3.5 ± 0.2 s-1 for the zeolite-Y electrode and the ZSM-5 electrode, respectively by the Laviron equation

Characterisation and spectral properties of surface adsorbed phenosafranine dye in zeolite-Y and ZSM-5: photosensitisation of embedded nanoparticles of titanium dioxide

Synthesis, characterisation and photosensitisation of titanium dioxide nanoparticles by phenosafranine dye adsorbed on the external surfaces of microporous materials were carried out. Titanium dioxide nanoparticles were anchored on the external surface as well as encapsulated in the cavities of porous zeolites. The composite materials are characterized using powder XRD and UV-visible diffuse reflectance spectroscopy. The organic dye phenosafranine is used as visible light absorbing sensitiser. Photosensitisation of the titanium dioxide nanoparticles deposited on the external surface of the microporous silicates are effected by the singlet excited states of phenosafranine and the mechanism of photosensitization is suggested to be static in nature. Photosensitisation of the TiO2 nanoparticles encapsulated in the cavities of the host is more efficient. In the case of the sensitisation of the TiO2 nanoparticles encapsulated inside the zeolite framework, the process is facilitated by the interaction between the host lattice with adsorbed water molecules and the excited state of the dye molecules at the outer surface of the host. The present investigation for the first time reports on the sensitization of TiO2 nanoparticles by the organic dye separated in space by the insulator host material

Photophysical and charge transport properties of pyrazolines

Pyrazoline, an intense green emitting molecule both in solution and solid state, with extended pi-conjugation has been synthesized via simple two-step reactions in high yields. Having the electron rich pyrazoline moiety with good redox behavior, pyrazolines can be potential candidates for charge transport material in organic electronic devices. UV-Visible absorption spectra of pyrazolines exhibit peaks below 400 nm, which is a desired feature for charge transport materials because it avoids interference with donor absorption that falls in the visible to NIR region. Electrochemical and theoretical studies show that the HOMO energy level lies at around -4.8 to 5.2 eV depending on the substituents, which is in fact compatible with the PEDOT: PSS/P3HT and work function of the ITO electrode. The experimental hole transport value, measured using the hole only device and space charge limited current (SCLC) method, was found to be in the range of 10(-5) to 10(-6) cm(2) V-1 s(-1), depending on the substituents. The maximum hole mobility calculated by theoretical methods for the pyrazolines is 0.75 cm(2) V-1 s(-1)