Incidence of Quantum Confinement on Dark Triplet Excitons in Carbon Nanotubes.

The photophysics of single-wall carbon nanotubes (SWCNTs) is intensively studied due to their potential application in light harvesting and optoelectronics. Excited states of SWCNTs form strongly bound electron-hole pairs, excitons, of which only singlet excitons participate in application relevant optical transitions. Long-living spin-triplet states hinder applications, but they emerge as candidates for quantum information storage. Therefore, knowledge of the triplet exciton energy structure, in particular in a SWCNT chirality dependent manner, is greatly desired. We report the observation of light emission from triplet state recombination, i.e., phosphorescence, for several SWCNT chiralities using a purpose-built spectrometer. This yields the singlet-triplet gap as a function of the SWCNT diameter, and it follows predictions based on quantum confinement effects. Saturation under high microwave power (up to 10 W) irradiation allows the spin-relaxation time for triplet states to be determined. Our study sensitively discriminates whether the lowest optically active state is populated from an excited state on the same nanotube or through Förster exciton energy transfer from a neighboring nanotube.

An optically detected magnetic resonance spectrometer with tunable laser excitation and wavelength resolved infrared detection.

We present the development and performance of an optically detected magnetic resonance (ODMR) spectrometer. The spectrometer represents advances over similar instruments in three areas: (i) the exciting light is a tunable laser source which covers much of the visible light range, (ii) the optical signal is analyzed with a spectrograph, (iii) the emitted light is detected in the near-infrared domain. The need to perform ODMR experiments on single-walled carbon nanotubes motivated the present development and we demonstrate the utility of the spectrometer on this material. The performance of the spectrometer is critically compared to similar instruments. The present development opens the way to perform ODMR studies on various new materials such as molecules and luminescent quantum dots where the emission is in the near-infrared range and requires a well-defined excitation wavelength and analysis of the scattered light.

[In vitro interaction of selegiline, riboflavin and light. Sensitized photodegradation of drugs. I]. / Szelegilin, riboflavin és fény in vitro kölcsönhatása. Fotoszenzibilizált gyógyszerbomlások. I.

Selegiline (Deprenyl, Jumex, Movergan etc.) is primarily used in the therapy of Parkinson's disease due to its neuroprotective, antidepressive and oxidative stress-preventing activities. Its prime effect is based upon the inhibition of the monoamine oxidase enzyme (MAO-B). The cofactor of this flavoenzyme is riboflavin (vitamin B2). Riboflavin, on the other hand, is an effective photosensitizer, with the capacity to promote the photodegradation of molecules (drugs, biological systems) which are otherwise stable against daylight. It has been studied whether this property of riboflavin is expressed against selegiline as well. This experiments proved that in the presence of riboflavin, both daylight and the light of daylight-lamps are sufficient to significantly decompose selegiline. The major decomposition product is methamphetamine.

Enhancement of methyldopa metabolism with barbiturate.

The spurious increase in serum catecholamine levels associated with methyldopa treatment can be reduced by the simultaneous administration of phenobarbitone. This accelerating effect of phenobarbitone on methyldopa metabolism has been demonstrated in relation to both adrenaline and noradrenaline, and investigations suggest that it is due to the effect of barbiturate on the activity of metabolizing enzymes.