Photochemical behavior of calix[4]resorcinarenes
(CRAs) and O-octaacetylated derivatives having
four
azobenzene residues at their lower rim in solutions and monolayers is
described. UV irradiation of an
O-octaacetylated CRA in homogeneous solution gave rise to a
photostationary state consisting of a possible
six isomers as a result of normal photoisomerization. The compound
exhibited reversible precipitation/dissolution cycles in a diluted methanol solution upon alternate
irradiation with UV and visible light owing
to its scarce solubility of all-trans isomer.
Wherease azobenzene chromophores tethered from the
cyclic
skeleton displayed marked intermolecular interactions in monolayers on
a water surface, trans-to-cis
photoisomerization took place even in compressed monolayers. The
level of the photoisomerizability was
dependent on the chemical structure and surface pressures.
Monolayers of azobenzene CRAs exhibited
the reversible alteration of their areas under a constant surface
pressure upon UV and visible light irradiation
because of the drastic shape change of the chromophores.
SYNOPSISGas permeabilities across poly (chloro-p-xylylene) (parylene C ) films are measured with different thicknesses of 20.2,10.0,8.9,4.6,3.4, and 1.0 pm. Measurements were carried out below 1 atm and between 10 and 80°C, which are under the glass transition temperature. The temperature and pressure dependencies of the permeability and the apparent diffusion coefficients were measured. If the membrane thickness is larger than 8 pm, the gas-transport mechanism is solution-diffusion, which implies that it is pinhole-free, because the pressure dependency of the permeability cannot be found and the apparent activation energy of permeation and diffusion are observed. If the membrane thickness is less than 8 pm, the gas transport mechanism is pore flow combined with solution-diffusion flow because gas may penetrate both the porous area and the polymer matrix. The thinner the membrane, the higher is the permeability coefficient, since the diameter and number of pores increase with decrease of the membrane thickness. The gas permeability coefficient has different values at the same pressure or temperature. As this film is in the glassy state, it should be explained using the average ordering parameter (0, which is a function of temperature, pressure, gas concentration, and time.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.