Enlarged pore sizes are associated with increased sebum output level, age and male sex. In female patients, additional hormonal factors, such as those of the menstrual cycle, affect the pore size.
Excited-state dynamic planarization processes play a crucial role in determining exciton size in cyclic systems, as reported for π-conjugated linear oligomers. Herein, we report time-resolved fluorescence spectra and molecular dynamics simulations of π-conjugated cyclic oligothiophenes in which the number of subunits was chosen to show the size-dependent dynamic planarization in the vicinity of a ring-to-linear behavioral turning point. Analyses on the evolution of the total fluorescence intensity and the ratio between 0-1 to 0-0 vibronic bands suggest that excitons formed in a cyclic oligothiophene composed of six subunits fully delocalize over the cyclic carbon backbone, whereas those formed in larger systems fail to achieve complete delocalization. With the aid of molecular dynamics simulations, it is shown that distorted structures unfavorable for efficient exciton delocalization are more easily populated as the size of the cyclic system increases.
Hexakis[p-(hydroxymethyl)phenoxy]cyclotriphosphazene was prepared by the reaction of hexachlorocyclotriphosphazene with the sodium salt of 4-hydroxy benzaldehyde and subsequent reduction of aldehyde groups to alcohol groups by using sodium borohydride. The bromination reaction was carried out by using hydrobromic acid-sulfuric acid to give hexakis[p-(bromomethyl)phenoxy]cyclotriphosphazene. This compound was employed in initiating polymerization of 2-methyl-2-oxazoline to produce six-armed, star-branched polymers. Monofunctional initiator, NsPatOCeHeWOCe^-p-C^Br), was also prepared and used for initiating the polymerization of 2-methyl-2-oxazoline to result in linear polymers. Molecular weights and DP's per an arm of the polymers were determined by gel permeation chromatography and NMR, respectively. The molecular weight of the linear polymer measured by GPC was much higher than that of the star-branched polymer when their molecular weights determined by NMR were nearly same. The linear polymer (DP = 31) with a bulky hydrophobic head and a hydrophilic chain exhibited nonionic surfactant behavior, forming micelles above a polymer concentration of about 0.1% by weight. The star-branched polymers had a hydrophobic core and hydrophilic branches. The surface tension of the aqueous solution of the star-branched polymer (DP = 13.4 per branch) decreased very slowly as polymer concentration increased, and any evidence for forming micelles was not observed. N-Acetyl groups of star-branched polymers were removed by hydrolysis under acidic conditions to give the polymers with N-protonated poly(ethylenimine) branches.
Polymerizable disklike compounds that have a benzene ring core and three rigid
diacetylenic units were prepared. The diacetylenic units were attached to the benzene ring
via ester linkages. By varying number of alkoxy tail carbons and benzene rings of the disk,
the morphological change of the compounds and their polymerization were investigated by
differential scanning calorimetry (DSC), polarizing optical microscopy, infrared spectroscopy
(IR), and powder X-ray diffraction (XRD). Compound 7 with no alkoxy tail was glassy or
small crystals at room temperature and showed crystal-to-crystal phase transition when
heated. Compounds 8 with butyloxy tails, 9 with hexyloxy tails, and 10 with octyloxy tails
showed monotropic transitions. When the compounds were cooled from the isotropic liquid
states, birefringent phases with mosaic textures were observed. XRD study showed that
compounds 9 and 10 had hexagonal columnar structures in their liquid crystalline (LC)
states. The diacetylene compounds were polymerized by irradiation with UV in solid states
or LC states. IR and UV−vis studies showed that the polymerization proceeded by 1,4-addition.
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