Double hydrogen transfer was monitored in single molecules of parent porphycene and its tetra- t-butyl derivative using confocal fluorescence microscopy. The molecules have been embedded in a polymer matrix. Under such conditions, a significant fraction of the population reveals a huge decrease of the tautomerization rate with respect to the value obtained from ensemble studies in solution. This effect is explained by a model that assumes that the rate is determined by the reorganization coordinate that involves slow relaxation of the polymer matrix. The model provides indirect evidence for the dominant role of tunneling. It is proposed that tautomerization in single molecules of the porphycene family can be used to probe polymer relaxation dynamics on the time scale ranging from picoseconds to minutes.
Different forms of iron compounds embedded in non‐functionalized (as prepared) and functionalized multiwall carbon nanotubes (MWCNTs) were studied. Iron used to catalyze MWCNT synthesis can be found inside nanotubes and built‐in within their walls. Mössbauer spectroscopy was applied to study valence and spin states as well as magnetic ordering of the iron compounds. In the Mössbauer spectra of as prepared MWCNTs the Fe3C carbide provides the main contribution. The content of Fe3C decreases by about 20 and 40% in carboxylated carbon nanotubes (MWCNTs‐COOH) and ammonium salt of carboxylated carbon nanotubes (MWCNTs‐COONH4), respectively. A small amount of α‐Fe and FexCx iron forms are always observed in all studied carbon nanotubes. In MWCNTs‐COOH, additionally, ferrihydrates and/or FexCy with oxygen in the second coordination sphere of iron are present (at a level of about 17%). In MWCNTs‐COONH4 their content increases by a factor of 3. The experimental data shows that the purification and functionalization of as prepared MWCNTs result in removal of about 90% of iron contaminations. Additionally, we observe the modification of iron compounds inside MWCNTs. All these results are important in optimizing the as prepared MWCNT purification process and in finding a new way to produce different Fe phases inside MWCNTs.
We investigated Fe‐phases of iron complexes embedded in nonfunctionalized (as‐prepared) and functionalized multi‐wall carbon nanotubes (MWCNTs). Mössbauer spectroscopy is a very sensitive tool to study chemical states of iron compounds embedded in MWCNTs. It showed that the chemical treatment of the as‐prepared MWCNTs caused release of about 84% of iron and modification of the remaining iron compounds. In as‐prepared and carboxylated MWCNTs almost 80 and 75% of iron complexes in a form of Fe3C exhibited magnetic ordering even at room temperature, respectively. In MWCNT‐COONH4 only 50% of such iron compounds showed local magnetic ordering. In all cases about 2% of magnetic α‐Fe fraction was detected. Through the dc magnetization and transmission electron microscopy (TEM) measurements it was proved that cementite nanoparticles formed agglomerates and their sizes were larger than 10 nm. STM measurements indicated increased homogeneity of the surface electric properties in the case of chemically treated carbon nanotubes.
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.