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 which assumes that the rate is determined by the reorganization coordinate which 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.

Successful generation of ultrashort pulses in the spectral region of 920 nm using Nd-doped fibers requires effectively suppressing the dominant 1064 nm four-level transition. Utilizing a hybrid design incorporating a W-shaped double-clad Nd-doped fiber and a single-clad Nd-doped fiber together with filtering out parasitic 1.06 µm beam, we developed an oscillator capable of delivering ultrashort pulses at the central wavelength of 929 nm. Here, we transferred the crucial components of the technology from the well-developed Yb-doped systems to build an all-polarization-maintaining Nd-doped fiber laser oscillator. The ultrashort pulsed operation is obtained through the passive mode-locking via a nonlinear amplifying loop mirror based on a 3x3 fiber coupler. The self-starting system has a figure-of-8 all-normal-dispersion cavity design and operates in a dissipative soliton regime. The oscillator, generating pulses with energy exceeding 1 nJ, delivers chirped 14.3 ps pulses, which can be compressed to 313 fs.

The influence of the grinding process on the magnetic properties of as prepared and functionalized multiwall carbon nanotubes (MWCNTs) is presented. We have observed that 3 h mechanical grinding at 400 rpm in contrast to functionalization does not remove the iron contamination from MWCNTs. However, it changes the Fe chemical states. The magnetic properties of iron nanoparticles (Fe-NPs) embedded in the carbon matrix of MWCNTs have been analyzed in detail. We have proven that single-domain non-interacting Fe_(C,O)-NPs enriched in the Fe₃C phase (~10 nm) enclosed inside these nanotubes are responsible for their magnetic properties. Mechanical grinding revealed a unique impact of -COOH groups (compared to -COONH₄ groups) on the magnetism of functionalized MWCNTs. In MWCNT-COOH ground in a steel mill, the contribution of the Fe₂O₃ and α-Fe phases increased while the content of the magnetically harder Fe₃C phase decreased. This resulted in a 2-fold coercivity (H_c) decrease and saturation magnetization (M_S) increase. A 2-fold remanence (M_r) decrease in MWCNT-COOH ground in an agate mill is related to the modified Fe_(C,O)-NP magnetization dynamics. Comparison of the magnetostatic exchange and effective anisotropy length estimated for Fe_(C,O)-NPs allows concluding that the anisotropy energy barrier is higher than the magnetostatic energy barrier. The enhanced contribution of surface anisotropy to the effective anisotropy constant and the unique effect of the -COOH groups on the magnetic properties of MWCNTs are discussed. The procedure for grinding carboxylated MWCNTs with embedded iron nanoparticles using a steel mill has a potential application for producing Fe-C nanocomposites with desired magnetic properties.