TY - JOUR A1 - Hennig, Andreas A1 - Hatami, Soheil A1 - Spieles, Monika A1 - Resch-Genger, Ute T1 - Excitation energy migration and trapping on the surface of fluorescent poly(acrylic acid)-grafted polymer particles N2 - The surface of poly(methyl methacrylate) particles with different amounts of a grafted layer of poly(acrylic acid) was labeled with varying degrees of an amino derivative of fluorescein isothiocyanate. The resulting fluorescent polymer particles were analyzed by absorption spectroscopy and by steady-state and time-resolved fluorescence spectroscopy including measurements of the fluorescence anisotropy. The combined results indicate that the overall decrease in fluorescence intensity with increasing surface concentrations of the fluorophore can be traced back to the formation of non-fluorescent aggregates. A mechanism is proposed, in which the excitation energy migrates between identical fluorophores until it is transferred to non-fluorescent aggregates acting as an energy trap. Increases in the surface fluorophore concentration increase both the probability for energy transfer between identical fluorophores and the probability for energy transfer to non-fluorescent aggregates. Furthermore, we suggest that this mechanism also applies to fluorescent protein conjugates and rationalizes the nonlinear dependence of the fluorescence emission on the labeling density. PY - 2013 U6 - https://doi.org/10.1039/c2pp25364j SN - 1474-905X SN - 1474-9092 VL - 12 IS - 5 SP - 729 EP - 737 PB - Royal Society of Chemistry CY - Cambridge AN - OPUS4-28522 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Leubner, S. A1 - Hatami, Soheil A1 - Esendemir, Nehir A1 - Lorenz, T. A1 - Joswig, J.-O. A1 - Lesnyak, V. A1 - Recknagel, Sebastian A1 - Gaponik, N. A1 - Resch-Genger, Ute A1 - Eychmüller, A. T1 - Experimental and theoretical investigations of the ligand structure of water-soluble CdTe nanocrystals N2 - The unique optical properties, such as size-tunable absorption and emission, caused semiconductor nanocrystals to attract a great deal of interest for recent technological developments. For the evaluation of semiconductor nanocrystals as new materials for various applications like optoelectronic devices, knowledge of the structure–property relationships is indispensable, but still presents a challenge. Here, we address these challenges for thioglycolic acid-capped CdTe nanocrystals with a focus on the quantification of thiol ligands, identification of the ligand shell structure and their influence on the optical properties of these nanocrystals. We present the use of a simple analytical technique, the Ellman's test, and ICP-OES analysis for the study of the surface chemistry of these nanomaterials. Together with theoretical calculations, the results of these studies show the strong influence of the amount of Cd–thiolates present in the ligand shell on the concentration-dependent emission properties, thereby providing the basis for a better understanding of the chemical nature of the NC–ligand interface. In this context, the present work contributes to the establishment of a clearer picture and better control of the surface chemistry, which will provide the basis for the design of highly emitting nanocrystals and the prediction of their applicability. PY - 2013 U6 - https://doi.org/10.1039/c3dt50802a SN - 1477-9226 SN - 1477-9234 SN - 1364-5447 VL - 42 SP - 12733 EP - 12740 PB - RSC CY - Cambridge AN - OPUS4-29139 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -