We report on the synthesis, structure, and self-assembly of single-wall subnanometer-diameter molybdenum disulfide tubes. The nanotubes are up to hundreds of micrometers long and display diverse self-assembly properties on different length scales, ranging from twisted bundles to regularly shaped “furry” forms. The bundles, which contain interstitial iodine, can be readily disassembled into individual molybdenum disulfide nanotubes. The synthesis was performed using a novel type of catalyzed transport reaction including C ₆₀ as a growth promoter.

Ultrafast transient reflectivity changes caused by collective and single particle excitations in the quasi-one-dimensional charge-density wave (CDW) semiconductor ${\mathrm{K}}_{0.3}{\mathrm{MoO}}_3$ are investigated with optical pump-probe spectroscopy. The temperature dependence of nonequilibrium single particle excitations across the CDW gap and their recombination dynamics are reported for the first time. In addition, amplitude mode reflectivity oscillations are observed in real time. A $T$-dependent overdamped response is also observed which is attributed to relaxation of the phason mode.

We present a comparative study of ultrafast photoconversion dynamics in tetracene (Tc) and pentacene (Pc) single crystals and Pc films using optical pump-probe spectroscopy. Photoinduced absorption in Tc and Pc crystals is activated and temperature-independent, respectively, demonstrating dominant singlet-triplet exciton fission. In Pc films (as well as ${\mathrm{C}}_{60}$-doped films) this decay channel is suppressed by electron trapping. These results demonstrate the central role of crystallinity and purity in photogeneration processes and will constrain the design of future photovoltaic devices.