TY - JOUR A1 - Witte, F. A1 - Rietsch, P. A1 - Sinha, S. A1 - Krappe, A. A1 - Joswig, J.-O. A1 - Götze, J. P. A1 - Nirmalananthan-Budau, Nithiya A1 - Resch-Genger, Ute A1 - Eigler, S. A1 - Paulus, B. T1 - Fluorescence Quenching in J‑Aggregates through the Formation of Unusual Metastable Dimers N2 - 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. KW - Fluorescence KW - Llifetime KW - Dye KW - Quantum yield KW - Label KW - Reporter KW - Aggregation KW - Monomer KW - Heory KW - Mechanism KW - photophysics PY - 2021 DO - https://doi.org/10.1021/acs.jpcb.1c01600 SN - 1520-5207 VL - 125 IS - 17 SP - 4438 EP - 4446 PB - ACS Publikations AN - OPUS4-52619 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Witke, Klaus A1 - Dietrich, D. A1 - Marx, G. A1 - Götze, J. A1 - Rößler, R. T1 - Cathodoluminescence and RAMAN studies on permineralisations of medullosa sp. T2 - 11. Tagung Festkörperanalytik CY - Chemnitz, Germany DA - 2001-06-25 PY - 2001 PB - GDCh CY - Frankfurt am Main AN - OPUS4-1057 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Witke, Klaus A1 - Dietrich, D. A1 - Götze, J. A1 - Rößler, R. A1 - Marx, G. T1 - Cathodoluminescence microscopy and micro-RAMAN spectroscopy on Medullos stellata v. COTTA - a contribution to the study of the permineralisation process KW - CL microscopy KW - CL Spectroscopy KW - RAMAN spectroscopy KW - Permineralisation PY - 2001 SN - 0937-0633 PB - Springer CY - Berlin AN - OPUS4-1079 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Witke, Klaus A1 - Götze, J. A1 - Rößler, R. A1 - Dietrich, D. A1 - Marx, G. T1 - Raman and cathodoluminescence spectroscopic investigations on Permian fossil wood from Chemnitz - a contribution to the study of the permineralisation process N2 - Samples of different three-dimensionally preserved fossil plants (Medullosa sp., Dadoxylon sp., Calamodendron striatum, Psaronius sp.) from the Lower Permian petrified forest of Chemnitz were examined with regard to their chemical composition and structural order. Raman spectroscopy and cathodoluminescence microscopy are shown to be powerful tools for such investigations. Silicified wood from Chemnitz–Hilbersdorf generally shows yellow cathodoluminescence (CL) of the cell walls and only weak yellow-brownish CL of the cell lumina. By time-resolved cathodoluminescence spectroscopy, a secondary mineralisation of hydrothermal origin was recognized. The latter is shown by short-lived blue CL at the cell walls extinguishing the yellow signal. Therefore, after the primary silicification step a secondary mineralisation step initiated by hydrothermal processes, seems to have taken place at probably slightly higher temperatures. The resulting silica matrix consists of phanerocrystalline and microcrystalline a-quartz as well as microcrystalline moganite, both partially associated with iron oxides. Dadoxylon sp. is a prominent example for parallel permineralisation by a-quartz and fluorspar, which is outstanding for the Chemnitz Petrified Forest. CL on this samples shows parallel silicification and fluoritisation, followed by infiltration of iron oxides. Permineralised samples show very low percentage of original organic remains. The seed fern Medullosa, for example, shows dispersed carbon, which is mainly restricted to the centres of the typical star-shaped vascular bundles. Raman spectroscopy revealed that these carbonaceous particles are of an anthracite structure. For experimental confirmation coal samples of different rank, especially anthracite from different geological times and localities, were studied by means of Raman spectroscopy. The remaining pith of the vascular bundles is white-coloured and consists of a-quartz and moganite, whereas surrounding tracheides exhibit white and reddish coloured parts. The reddish parts, mainly found in the rays, additionally contain a-Fe2O3 and Fe3O4 among the SiO2 polymorphs of a-quartz and moganite. Sometimes iron oxides could have dominated permineralisation processes as the peak intensities of distinct parts of the samples suggest. KW - Raman spectroscopy KW - Cathodoluminescence microscopy KW - Petrified wood KW - Permineralisation KW - Anthracite PY - 2004 UR - http://www.sciencedirect.com/science?_ob=PublicationURL&_cdi=5287&_pubType=J&_auth=y&_acct=C000049503&_version=1&_urlVersion=0&_userid=963821&md5=ebfde1a480f4ae6a3eb0052a1b8e7c2a&jchunk=60#60 DO - https://doi.org/10.1016/j.saa.2003.12.045 SN - 0584-8547 SN - 0038-6987 VL - 60 IS - 12 SP - 2903 EP - 2912 PB - Elsevier CY - Amsterdam AN - OPUS4-4122 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Witte, F. A1 - Rietsch, P. A1 - Nirmalananthan-Budau, Nithiya A1 - Weigert, Florian A1 - Götze, J. P. A1 - Resch-Genger, Ute A1 - Eigler, S. A1 - Paulus, B. T1 - Aggregation-induced emission leading to two distinct emissive species in the solid-state structure of high-dipole organic chromophores N2 - The concept of aggregation-induced emission represents a means to rationalise photoluminescence of usually nonfluorescent excimers in solid-state materials. In this publication, we study the photophysical properties of selected diaminodicyanoquinone (DADQ) derivatives in the solid state using a combined approach of experiment and theory. DADQs are a class of high-dipole organic chromophores promising for applications in non-linear optics and light-harvesting devices. Among the compounds investigated, we find both aggregation-induced emission and aggregation-caused quenching effects rationalised by calculated energy transfer rates. Analysis of fluorescence spectra and lifetime measurements provide the interesting result that (at least) two emissive species seem to contribute to the photophysical properties of DADQs. The main emission peak is notably broadened in the long-wavelength limit and exhibits a blue-shifted shoulder. We employ high-level quantum-chemical methods to validate a molecular approach to a solid-state problem and show that the complex emission features of DADQs can be attributed to a combination of H-type aggregates, monomers, and crystal structure defects. KW - Fluorescence KW - Optical probe KW - Dye KW - Photophysics KW - Theory KW - Quantum yield KW - Mechanism KW - Quantum chemistry KW - Modelling KW - Aggregation KW - Lifetime KW - Single particle KW - Microscopy KW - Solid KW - Crystal PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-531138 DO - https://doi.org/10.1039/d1cp02534a SP - 1 EP - 9 PB - Royal Society of Chemistry AN - OPUS4-53113 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -