Migration of Excitation Energy in Furocoumarins

The migration of excitation energy of a number of psoralen compounds has been studied. For this, the methods of induced absorption spectroscopy, stationary electron spectroscopy, fluorescence and phosphorescence, as well as quantum chemistry were used. A comparative photostability of psoralen was achieved by exposure to a XeCl excilamp irradiation (emission wavelength λem = 308 nm) with parameters Δλ = 5–10 nm, Wpeak = 18 mW/cm2, p = 8.1 J/cm3, f = 200 kHz, pulse duration 1 μs. It was found that the singlet-triplet transition played a major role in the migration of excitation energy into triplet states. Among all tested compounds, substances with an OCH3-group in the structure have the strongest effect on the spectral-luminescent characteristics.

MONTE CARLO STUDIES OF ELECTRONIC TRANSPORT IN HELICALLY COILED CARBON NANOTUBES

We studied the stationary electron transport of semiconduction single-wall straight and helically coiled carbon nanotubes in the presence of electron- phonon interaction. The electron and phonon bands as well as electron phonon coupling matrix elements are obtained from quantum mechanical calculations with the application of symmetry. Total scattering rate for all electronic states relevant for charge transport is obtained as a sum over independent processes. Transport simulation is realized by Monte Carlo algorithm, where free flight time and scattering mechanism are selected randomly. The obtained electron transport properties of helically coiled and straight carbon nanotubes are significantly different. The electron drift velocities in helically coiled nanotubes are several times lower than in straight carbon nanotubes.