TY - JOUR A1 - Hattori, Yohei A1 - Michail, Evripidis A1 - Schmiedel, Alexander A1 - Moos, Michael A1 - Holzapfel, Marco A1 - Krummenacher, Ivo A1 - Braunschweig, Holger A1 - Müller, Ulrich A1 - Pflaum, Jens A1 - Lambert, Christoph T1 - Luminescent Mono-, Di-, and Tri-radicals: Bridging Polychlorinated Triarylmethyl Radicals by Triarylamines and Triarylboranes JF - Chemistry - A European Journal N2 - Up to three polychlorinated pyridyldiphenylmethyl radicals bridged by a triphenylamine carrying electron withdrawing (CN), neutral (Me), or donating (OMe) groups were synthesized and analogous radicals bridged by tris(2,6‐dimethylphenyl)borane were prepared for comparison. All compounds were as stable as common closed‐shell organic compounds and showed significant fluorescence upon excitation. Electronic, magnetic, absorption, and emission properties were examined in detail, and experimental results were interpreted using DFT calculations. Oxidation potentials, absorption and emission energies could be tuned depending on the electron density of the bridges. The triphenylamine bridges mediated intramolecular weak antiferromagnetic interactions between the radical spins, and the energy difference between the high spin and low spin states was determined by temperature dependent ESR spectroscopy and DFT calculations. The fluorescent properties of all radicals were examined in detail and revealed no difference for high and low spin states which facilitates application of these dyes in two‐photon absorption spectroscopy and OLED devices. KW - density functional calculations KW - fluorescence KW - NIR OLED KW - radical KW - two-photon absorption Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-208162 VL - 25 IS - 68 ER - TY - JOUR A1 - Lübtow, Michael M. A1 - Marciniak, Henning A1 - Schmiedel, Alexander A1 - Roos, Markus A1 - Lambert, Christoph A1 - Luxenhofer, Robert T1 - Ultra-high to ultra-low drug loaded micelles: Probing host-guest interactions by fluorescence spectroscopy JF - Chemistry - A European Journal N2 - Polymer micelles are an attractive means to solubilize water insoluble compounds such as drugs. Drug loading, formulations stability and control over drug release are crucial factors for drug‐loaded polymer micelles. The interactions between the polymeric host and the guest molecules are considered critical to control these factors but typically barely understood. Here, we compare two isomeric polymer micelles, one of which enables ultra‐high curcumin loading exceeding 50 wt.%, while the other allows a drug loading of only 25 wt.%. In the low capacity micelles, steady‐state fluorescence revealed a very unusual feature of curcumin fluorescence, a high energy emission at 510 nm. Time‐resolved fluorescence upconversion showed that the fluorescence life time of the corresponding species is too short in the high‐capacity micelles, preventing an observable emission in steady‐state. Therefore, contrary to common perception, stronger interactions between host and guest can be detrimental to the drug loading in polymer micelles. KW - curcumin KW - drug delivery KW - fluorenscence KW - poly(2-oxazine) KW - pol(2-oxazoline) KW - Polymer-drug interaction KW - upconversion Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-206128 VL - 25 IS - 54 ER - TY - INPR A1 - Auerhammer, Nina A1 - Schulz, Alexander A1 - Schmiedel, Alexander A1 - Holzapfel, Marco A1 - Hoche, Joscha A1 - Röhr, Merle I. S. A1 - Mitric, Roland A1 - Lambert, Christoph T1 - Dynamic exciton localisation in a pyrene-BODIPY-pyrene dye conjugate T2 - Physical Chemistry Chemical Physics N2 - The photophysics of a molecular triad consisting of a BODIPY dye and two pyrene chromophores attached in 2-position are investigated by steady state and fs-time resolved transient absorption spectroscopy as well as by field induced surface hopping (FISH) simulations. While the steady state measurements indicate moderate chromophore interactions within the triad, the time resolved measurements show upon pyrene excitation a delocalised excited state which localises onto the BODIPY chromophore with a time constant of 0.12 ps. This could either be interpreted as an internal conversion process within the excitonically coupled chromophores or as an energy transfer from the pyrenes to the BODIPY dye. The analysis of FISH-trajectories reveals an oscillatory behaviour where the excitation hops between the pyrene units and the BODIPY dye several times until finally they become localised on the BODIPY chromophore within 100 fs. This is accompanied by an ultrafast nonradiative relaxation within the excitonic manifold mediated by the nonadiabatic coupling. Averaging over an ensemble of trajectories allowed us to simulate the electronic state population dynamics and determine the time constants for the nonradiative transitions that mediate the ultrafast energy transfer and exciton localisation on BODIPY. KW - Exciton localization dynamics Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-198718 UR - https://doi.org/10.1039/C9CP00908F N1 - Accepted manuscript ER -