Dokument-ID Dokumenttyp Autoren/innen Persönliche Herausgeber/innen Haupttitel Abstract Auflage Verlagsort Verlag Herausgeber (Institution) Erscheinungsjahr Titel des übergeordneten Werkes Jahrgang/Band ISBN Veranstaltung Veranstaltungsort Beginndatum der Veranstaltung Enddatum der Veranstaltung Ausgabe/Heft Erste Seite Letzte Seite URN DOI Lizenz Datum der Freischaltung OPUS4-29139 Zeitschriftenartikel Leubner, S.; Hatami, Soheil; Esendemir, Nehir; Lorenz, T.; Joswig, J.-O.; Lesnyak, V.; Recknagel, Sebastian; Gaponik, N.; Resch-Genger, Ute; Eychmüller, A. Experimental and theoretical investigations of the ligand structure of water-soluble CdTe nanocrystals 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. Cambridge RSC Royal Society of Chemistry 2013 Dalton transactions 42 12733 12740 10.1039/c3dt50802a 2016-02-20 OPUS4-37125 Zeitschriftenartikel Schneider, Ralf; Weigert, Florian; Lesnyak, V.; Leubner, S.; Lorenz, T.; Behnke, Thomas; Dubavik, A.; Joswig, J.-O.; Resch-Genger, Ute; Gaponik, N.; Eychmüller, A. Resch-Genger, Ute; Schneider, Ralf pH and concentration dependence of the optical properties of thiol-capped CdTe nanocrystals in water and D2O The optical properties of semiconductor nanocrystals (SC NCs) are largely controlled by their size and surface chemistry, i.e., the chemical composition and thickness of inorganic passivation shells and the chemical nature and number of surface ligands as well as the strength of their bonds to surface atoms. The latter is particularly important for CdTe NCs, which - together with alloyed CdₓHg₁₋ₓTe - are the only SC NCs that can be prepared in water in high quality without the need for an additional inorganic passivation shell. Aiming at a better understanding of the role of stabilizing ligands for the control of the application-relevant fluorescence features of SC NCs, we assessed the influence of two of the most commonly used monodentate thiol ligands, thioglycolic acid (TGA) and mercaptopropionic acid (MPA), on the colloidal stability, photoluminescence (PL) quantum yield (QY), and PL decay behavior of a set of CdTe NC colloids. As an indirect measure for the strength of the coordinative bond of the ligands to SC NC surface atoms, the influence of the pH (pD) and the concentration on the PL properties of these colloids was examined in water and D₂O and compared to the results from previous dilution studies with a set of thiol-capped Cd₁₋ₓHgₓTe SC NCs in D₂O. As a prerequisite for these studies, the number of surface ligands was determined photometrically at different steps of purification after SC NC synthesis with Ellman's test. Our results demonstrate ligand control of the pH-dependent PL of these SC NCs, with MPA-stabilized CdTe NCs being less prone to luminescence quenching than TGA-capped ones. For both types of CdTe colloids, ligand desorption is more pronounced in H₂O compared to D₂O, underlining also the role of hydrogen bonding and solvent molecules. Cambridge RSC RSC 2016 Physical Chemistry Chemical Physics 18 28 19083 19092 urn:nbn:de:kobv:b43-371253 10.1039/c6cp03123d http://creativecommons.org/licenses/by-nc/3.0/de/deed.de 2016-08-12 OPUS4-52619 Zeitschriftenartikel Witte, F.; Rietsch, P.; Sinha, S.; Krappe, A.; Joswig, J.-O.; Götze, J. P.; Nirmalananthan-Budau, Nithiya; Resch-Genger, Ute; Eigler, S.; Paulus, B. Fluorescence Quenching in J‑Aggregates through the Formation of Unusual Metastable Dimers Molecular aggregation alters the optical properties of a system as fluorescence may be activated or quenched. This is usually described within the well-established framework of H- and J-aggregates. While H-aggregates show nonfluorescent blueshifted absorption bands with respect to the isolated monomer, Jaggregates are fluorescent displaying a redshifted peak. In this publication, we employ a combined approach of experiment and theory to study the complex aggregation features and photophysical properties of diaminodicyanoquinone derivatives, which show unusual and puzzling nonfluorescent redshifted Absorption bands upon aggregation. Our theoretical analysis demonstrates that stable aggregates do not account for the experimental observations. Instead, we propose an unprecedented mechanism involving metastable dimeric species formed from stable dimers to generate nonfluorescent J-aggregates. These results represent a novel kind of aggregation-induced optical effect and may have Broad implications for the photophysics of dye aggregates. ACS Publikations 2021 The Journal of Physical Chemistry 125 17 4438 4446 10.1021/acs.jpcb.1c01600 2021-05-12