169,808 research outputs found
Photophysics of soft and hard molecular assemblies based on luminescent complexes
No full textIn this chapter, we discuss several approaches that have led from molecular entities to supramolecular soft and hard molecular architectures. Systems based on metal complexes with d6 and d8 electronic configuration forming assemblies such as micelles, vesicles, and gels, as well as crystalline structures, will be illustrated. The focus is on the role played by the metal complexes chemical structures as well as the choice of the intermolecular interactions in the ground and/or excited electronic states within the arrays. The selected examples, based on noncovalently linked luminescent systems, aim to the development of multifunctional assemblies, in which the self-organization generates new functions, for potential applications in optically addressable materials. The question is how much we can rationalize the behavior and predict the structures and their properties on the basis of the design
Luminescent gels by self-assembling platinum complexes
No full textA platinum complex bearing a tetraethylene glycol chain has been designed and its self-assembly properties investigated. In solution, only a yellow phosphorescence of the aggregated species is observed. The complex gives luminescent gels of different colours with DCM and DMF, reaching up to 60% photoluminescence quantum yield. © 2012 The Royal Society of Chemistry
Switching on luminescence by the self-assembly of a platinum(II) complex into gelating nanofibers and electroluminescent films
No full textA platinum(II) emitter is able to self-assemble into gelating nanofibers, leading to an unprecedented 90 % photoluminescence quantum yield. Electroluminescent devices processed in solution can be doped with the aforementioned complex. Picture: a) Emission (α) and excitation spectra and photos of the gel, b) REM, and c) TEM images of the nanofibers
Tracking intramolecular interactions in flexibly linked binuclear Platinum(II) complexes
No full textIn this work we describe the synthesis and the photophysical and electrochemical characterization of binuclear PtII complexes. Using a modular click chemistry approach, we decorated different flexible bridging units with (bpy)PtII bisacetylides (bpy = 2,2′-bipyridine). Intramolecular excimer formation originating from PtII-Pt II and π-π interactions was investigated by steady-state and time-resolved emission spectroscopy in dilute solution. We observed that linkers bringing the metallic centers in close proximity favor both ground-state coupling and excimer formation. These interactions lead to changes in the photophysical and electrochemical properties, which can be tuned by the choice of solvent
Dipyrrin based luminescent cyclometallated palladium and platinum complexes
No full textA series of complexes based on the combination of cyclometallated palladium or platinum moieties with functionalized dipyrrin ligands bearing mesityl- or benzonitrile groups have been prepared and characterized both in the solid state and in solution; these compounds exhibit a characteristic dipyrrin-centered luminescence with an emission intensity modulated by the degree of rotational freedom of the aromatic group attached to the dipyrrin chelate
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Photofunctional surfaces for quantitative fluorescence microscopy: monitoring the effects of photogenerated reactive oxygen species at single cell level with spatiotemporal resolution
No full textHerein, we report on the implementation of photofunctional surfaces for the investigation of cellular responses by means of quantitative fluorescence microscopy. The developed substrates are able to produce reactive oxygen species under the fluorescence microscope upon irradiation with visible light, and the behavior of cells grown on these surfaces can be consequently investigated in situ and in real time. Moreover, a suitable methodology is presented to simultaneously monitor phototriggered morphological changes and the associated molecular pathways with spatiotemporal resolution employing time-resolved fluorescence anisotropy at the single cell level. The results showed that morphological changes can be complemented with a quantitative evaluation of the associated molecular signaling cascades for the unambiguous assignment of reactive oxygen species-related photoinduced apoptosis. Indeed, similar phenotypes are associated with different cellular processes. Our methodology facilitates the in vitro design and evaluation of photosensitizers for the treatment of cancer and infectious diseases with the aid of functional fluorescence microscopy.Fil: Stegemann, Linda. Westfalische Wilhelms Universitat; AlemaniaFil: Schuermann, Klaus C.. Institut Max Planck Fur Molekulare Physiologie; AlemaniaFil: Strassert, Cristian A.. Westfalische Wilhelms Universitat; AlemaniaFil: Grecco, Hernan Edgardo. Institut Max Planck Fur Molekulare Physiologie; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentin
Alkylated Aromatic Thioethers with Aggregation-Induced Emission Properties—Assembly and Photophysics
No full textIn this contribution, we present the synthesis and self-assembly of alkylated thioethers with interesting photophysical properties. To this end, the emission, absorption and excitation spectra in organic solvents and as aggregates in water were measured as well as the corresponding photoluminescence quantum yields and lifetimes. The aggregates in aqueous media were visualized and measured using transmission electron microscopy. Besides that, crystal structures of selected compounds allowed a detailed discussion of the structure–property relationship. Furthermore, the mesomorphic behavior was investigated using polarized optical microscopy (POM) as well as differential scanning calorimetry (DSC)
Bidentate NHC pyrozolate ligands in luminescent platinum(ii) complexes
No full textA bidentate C^N donor set derived from an N-heterocyclic carbene (NHC) precursor linked to a trifluoromethyl (CF3) functionalized pyrazole ring is described for the first time. The ligands have been employed to prepare four new phosphorescent complexes by the coordination of platinum(ii) centres bearing cyclometalated phenyl-pyridine/triazole-pyridine chelates. The electronic and steric environments of these complexes were tuned through the incorporation of suitable substituents in the phenyl-pyridine/triazole-pyridine ligands, wherein the position of the phenyl-ring substituent (a CF3 group) also directs the selective adoption of either a trans or a cis configuration between the CNHC and the Cphenyl donor atoms. Molecular structures obtained by X-ray diffraction for three of the complexes confirm a distorted square-planar configuration around the platinum centre, and DFT calculations show that the substituents have a significant influence on the energies of the frontier orbitals. Moreover, a platinum(ii) complex featuring the new bidentate NHC^pyrazolate ligand and a bulky adamantyl functionalized pyridine-triazole luminophore was observed to be highly emissive and exhibiting a sky-blue luminescence (λEm = 470 nm) with photoluminescence quantum yields as high as 50% in doped PMMA matrices. A complete photophysical investigation of all of the complexes in solution as well as in the solid state is herein reported
Correlating the Structural and Photophysical Features of Pincer Luminophores and Monodentate Ancillary Ligands in Pt-II Phosphors
No full textPhosphorescent PtII complexes featuring pincer luminophores of 2,6-bis(1,2,4-triazolyl)pyridine (H2L1) and 2,6-bis(pyrazolyl)pyridine (H2L3) with a bulky adamantyl or tolyl substituent (H2L4) are systematically compared, and their structural features are correlated with their photophysical properties. The combination with 4-amylpyridine (Py), triphenylphosphine (P) or benzimidazol-2-ylidene (N-heterocyclic carbene, NHC) donors as monodentate ancillary ligands gave a series of highly luminescent triplet emitters with variable aggregation properties. The molecular structures of four of these complexes, namely, Pt-L1-P, Pt-L1-NHC, Pt-L3-P, and Pt-L4-P were garnered from single-crystal X-ray diffraction analysis. The coordination complexes displayed green phosphorescence in solution and in the solid state. In doped poly(methyl methacrylate) (PMMA) matrices, most of the complexes exhibited high phosphorescence quantum yields, which reached 59 % for Pt-L3-P. A comparative analysis between the spectroscopic data and the computed parameters derived from time-dependent density functional theory (TD-DFT) calculations suggests that the emission originates from metal-perturbed ligand-centered excited triplet states (3MP-LC). The radiationless deactivation rate constants of the emissive states can be correlated with the aggregation properties derived from the substitution pattern at the tridentate luminophores and the ancillary ligands, whereas the radiative rate constants are determined by the electronic structures of the complexes. We found that PtII complexes containing pyrazolate donors showed an enhanced charge-transfer character in the excited state, whereas bulky adamantyl moieties and triphenylphosphine ancillary ligands suppress bimolecular aggregation and quenching phenomena
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