No abstract

We present a detailed study of the photophysical properties of a tetraphenoxy-substituted perylene bisimide derivative. The probe molecules were immobilized in a Shpol'skii matrix of hexadecane and investigated by single-molecule spectroscopy at cryogenic temperatures. By using single-molecule spectroscopic techniques we reveal the triplet substate kinetics and the fluorescence quantum yield, and we provide an estimate for the S1-S0 transition dipole moment.

Characterization of the photophysical parameters for three perylene bisimide derivatives is presented. We exploited time-resolved and steady-state spectroscopy on both ensembles and single molecules under ambient as well as cryogenic (1.4 K) conditions. The finding is that these chromophores show extraordinary high fluorescence-emission rates, low intersystem crossing yields to the triplet state, and relatively short triplet lifetimes.

Summary Epifluorescence, confocal and total internal reflection microscopy are the most widely used techniques for optical single‐molecule experiments. Employing these methods, we recorded the emission intensity of the same single molecule as a function of the excitation rate under otherwise identical experimental conditions. Evaluation of these data provides a quantitative comparison of the signal‐to‐background ratios that can be achieved for the three microscopic techniques.

The interaction of gas-phase H atoms with ordered and disordered adlayers of atomic oxygen, hydroxyl, and molecular oxygen on Pt͑111͒ surfaces was investigated by in situ mass spectrometry and post-reaction TPD ͑temperature programed desorption͒. Exposure of oxygen adlayers to gas-phase H atoms at 85 K leads to formation of H 2 O via two consecutive hydrogenation reactions: H(g)ϩO(a)→OH(a) followed by H(g)ϩOH(a)→H 2 O(g,a). Both reaction steps are highly exothermic, and nascent H 2 O molecules partially escape into the gas phase before being thermally accommodated on the surface. Empty surface sites and hydrogen bonding promote thermalization of H 2 O. Separate experiments performed with OH-covered Pt͑111͒ surfaces reveal that the hydrogenation of hydroxyl is a slow reaction compared to the hydrogenation of atomic oxygen; additionally, the abstraction of H from OH by gas-phase D atoms, OH(a)ϩD(g)→O(a) ϩHD(g), was detected. Abstraction of H from adsorbed H 2 O was not observed. Admission of gas-phase H atoms to O 2 -covered Pt͑111͒ surfaces at 85 K leads to the desorption of O 2 and H 2 O. The thermodynamic stability of the HO 2 radical suggests that the reaction is initiated by hydrogenation of molecular oxygen, O 2 (a)ϩH (g)→HO 2 . The intermediate HO 2 either decomposes via dissociation of the HO-O bond, HO 2 →OH(a)ϩO(a), finally leading to the formation of H 2 O ͑ϳ85%͒, or via dissociation of the H-O 2 bond thus leading to desorption of O 2 ͑ϳ15%͒. The whole reaction sequence of formation and decomposition of HO 2 is fast compared to the formation of H 2 O via hydrogenation of atomic oxygen and hydroxyl. The observed coverage dependence of the reaction kinetics indicates the dominance of hot-atom mediated reactions.