No abstract

Two asymmetrically substituted porphyrins (5,15-bis(4-nitrophenyl)-10,20-bis(3,4-bis(2-ethylhexyloxy)phenyl)-21H,23H-porphine, CAH3; 5,15-bis(4-aminophenyl)-10,20-bis(3,4-bis(2-ethylhexyloxy)phenyl)-21H,23H-porphine, CAH4) have been used in this work. Good Langmuir monolayers of these compounds have been prepared on water and transferred successfully to glass slides at much faster than conventional deposition rates (500 mm min -1 ). The monolayer behavior has been investigated by measuring surface pressure-area isotherms as well as by Brewster angle microscopy (BAM) and reflection spectroscopy. For both porphyrins, the intermolecular π-π interaction is sufficiently strong that significant preaggregation occurs prior to compression of the film. However, as the monolayers are compressed, changes in the molecular association and orientation are observed for CAH4 while no molecular reorganization is appreciated for CAH3. The different molecular packing of the Langmuir monolayers is maintained during the transfer. The UV-vis spectra of CAH3 and CAH4 solutions, respectively, were found to be sensitive to NO2 gas. However, only the Langmuir-Blodgett (LB) assemblies of CAH4 showed a response in the presence of the toxic gas. This different behavior has been explained in terms of the different molecular organization of the two porphyrins.

CdS nanoparticles have been formed within Langmuir−Blodgett (LB) films of cadmium salts of calix[8]- and calix[4]arene by reaction with hydrogen sulfide gas. The presence of CdS nanoparticles in the LB film matrices was checked by measurement of UV−vis absorption spectra, which allows an estimation of the size of the particles. It was shown that smaller particles (1.5 ± 0.3 nm) are formed in calixarene LB films than in Cd stearate films (used for comparison). The particle size does not depend on the type of calixarene or the number of LB layers but increases with increasing pH of the subphase. The formation of CdS was directly confirmed with XPS.

Seven different porphyrin compounds have been investigated as colorimetric gas sensors for a wide range of volatile organic compounds. The porphyrins examined were the free base and Mg, Sn, Zn, Au, Co, and Mn derivatives of 5,10,15,20-tetrakis[3,4-bis(2-ethylhexyloxy)phenyl]-21H,23H-porphine. Chloroform solutions of these materials were prepared and changes in their absorption spectra induced by exposure to various organic compounds measured. The porphyrins that showed strong responses in solution were selected, and Langmuir-Blodgett films were prepared and exposed to the corresponding analytes. This was done to determine whether they are useful materials for solid state thin film colorimetric vapor sensors. Porphyrins that readily coordinate extra ligands are shown to be suitable materials for colorimetric volatile organic compound detectors. However, porphyrins that already have bound axial ligands when synthesized only show a sensor response to those analytes that can substitute these axial ligands. The Co porphyrin displays a considerably larger response than the other porphyrins investigated which is attributed to a switch between Co(II) and Co(III) resulting in a large spectral change.