Highly luminescent gold nanoparticles: effect of ruthenium distance for nanoprobes with enhanced lifetimes

The photophysical properties of gold nanoparticles, AuNPs, with sizes of 13, 50 and 100 nm in diameter, coated with surface-active ruthenium complexes have been studied to investigate the effect of the distance of the ruthenium luminescent centre from the gold surface. Luminescence lifetimes of the three ruthenium probes, RuS1, RuS6 and RuS12, with different length spacer units between the surface active groups and the ruthenium centre were taken. The metal complexes were attached to AuNP13, AuNP50 and AuNP100via thiol groups using a method of precoating the nanoparticles with a fluorinated surfactant. The luminescence lifetime of the longer spacer unit complex, RuS12, was enhanced by 70% upon attachment to the AuNP when compared to the increase of the short and medium linker unit complexes, RuS1 (20%) and RuS6 (40%) respectively. The effect of the surfactant in the lifetime increase of the ruthenium coated AuNPs was shown to be larger for the medium spacer probe, RuS6. There was no effect of the change of the size of the AuNPs from 13 to 50 or 100 nm.

Temperature Dependence of Limiting Fluorescence Anisotropy of POPOP in Cellulose Acetate Film

The effect of temperature (103 K < T < 303 K) upon the limiting fluorescence anisotropy r0 of POPOP was investigated in a cellulose acetate film. A slow increase in r0 was observed when reducing the temperature. Based on the Jabłoński theory, the frequency of the torsional vibrations of POPOP was determined to be w = 1.3 x 1012s−1. The depolarization due to these torsional vibrations was found to occur immediately following excitation during the thermal relaxation of the luminescent centre, thus somewhat lowering the value of the fundamental fluorescence anisotropy rf to the limiting r0 value.

Energieübertragung zwischen gleich-und ungleichartigen Molekülen in Lösung III. Experimente über Fluoreszenzlöschung durch absorbierende Fremdstoffe/ Energy Transfer Among Like and Unlike Molecules in Solution III. Study of Fluorescence Quenching by Foreign Absorbing Substances

Energy Transfer Among Like and Unlike Molecules in Solution 111. Study of Fluorescence Quenching by Foreign Absorbing Substances Radiationless energy transfer between unlike molecules (heterotransfer) in fluid solutions was studied by the quenching of fluorescence by foreign absorbing substances. The quenching of electronic excitation energy of 2-aminopurine and 2-aminopyrimidine, acting as sensitizers, and by acridine or 9-methylanthracene, acting as acceptors, was investigated in ethanol and compared with the theory of "multi-shell model" of a luminescent centre. In fluid solutions the critical distance for energy transfer is little depended on the diffusion. Good agreement was found with the equation taking into account only the excitation energy migration.