Browsing by Subject "PHOTOPHYSICAL PROPERTIES"

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  • Valiev, Rashid R.; Cherepanov, Victor N.; Nasibullin, Rinat T.; Sundholm, Dage; Kurten, Theo (2019)
    Effective and fast algorithms for calculating rate constants for internal conversion (IC) and intersystem crossing (ISC) in the Franck-Condon and Herzberg-Teller approximations have been developed and implemented. The methods have been employed for calculating IC and ISC rate constants for the pyrromethene-567 dye (PM567), hetero[8]circulene (4B) and free-base porphyrin (H2P). The fluorescence quantum yields obtained by comparing calculated rate constants for the radiative and non-radiative processes are in good agreement with experimental data.
  • Shakirova, Julia R.; Sadeghi, Amir; Koblova, Alla A.; Chelushkin, Pavel S.; Toropainen, Elisa; Tavakoli, Shirin; Kontturi, Leena-Stiina; Lajunen, Tatu; Tunik, Sergey P.; Urtti, Arto (2020)
    Two iridium [Ir(NC)(2)(NN)](+) complexes with the diimine NN ligand containing a long polymethylene hydrophobic chain were synthesized and characterized by using NMR and ESI mass-spectrometry: NN - 2-(1-hexadecyl-1H-imidazol-2-yl)pyridine, NC - methyl-2-phenylquinoline-4-carboxylate (Ir1) and 2-phenylquinoline-4-carboxylic acid (Ir2). These complexes were used to prepare the luminescent PEGylated DPPC liposomes (DPPC/DSPE-PEG2000/Ir-complex = 95/4.5/1 mol%) using a thin film hydration method. The narrowly dispersed liposomes had diameters of about 110 nm. The photophysics of the complexes and labeled liposomes were carefully studied. Ir1 and Ir2 give red emission (lambda(em) = 667 and 605 nm) with a lifetime in the microsecond domain and quantum yields of 4.8% and 10.0% in degassed solution. Incorporation of the complexes into the liposome lipid bilayer results in shielding of the emitters from interaction with molecular oxygen and partial suppression of excited state nonradiative relaxation due to the effect of the relatively rigid bilayer matrix. Delivery of labeled liposomes to the cultured ARPE-19 cells demonstrated the usefulness of Ir1 and Ir2 in cellular imaging. Labeled liposomes were then injected intravitreally into rat eyes and imaged successfully with optical coherence tomography and funduscopy. In conclusion, iridium complexes enabled the successful labeling and imaging of liposomes in cells and animals.
  • Valiev, R. R.; Cherepanov, V. N.; Baryshnikov, G. V.; Sundholm, D. (2018)
    A method for calculating the rate constants for internal-conversion (k(IC)) and intersystem-crossing (k(ISC)) processes within the adiabatic and Franck-Condon (FC) approximations is proposed. The applicability of the method is demonstrated by calculation of k(IC) and k(ISC) for a set of organic and organometallic compounds with experimentally known spectroscopic properties. The studied molecules were pyrromethene-567 dye, psoralene, hetero[8]circulenes, free-base porphyrin, naphthalene, and larger polyacenes. We also studied fac-Alq(3) and fac-Ir(ppy)(3), which are important molecules in organic light emitting diodes (OLEDs). The excitation energies were calculated at the multi-configuration quasi-degenerate second-order perturbation theory (XMC-QDPT2) level, which is found to yield excitation energies in good agreement with experimental data. Spin-orbit coupling matrix elements, non-adiabatic coupling matrix elements, Huang-Rhys factors, and vibrational energies were calculated at the time-dependent density functional theory (TDDFT) and complete active space self-consistent field (CASSCF) levels. The computed fluorescence quantum yields for the pyrromethene-567 dye, psoralene, hetero[8]circulenes, fac-Alq(3) and fac-Ir(ppy)(3) agree well with experimental data, whereas for the free-base porphyrin, naphthalene, and the polyacenes, the obtained quantum yields significantly differ from the experimental values, because the FC and adiabatic approximations are not accurate for these molecules.
  • Valiev, Rashid; Kurten, Theo; Valiulina, Lenara I.; Ketkov, Sergey Yu.; Cherepanov, Viktor N.; Dimitrova, Maria; Sundholm, Dage (2022)
    The magnetically induced current-density susceptibility tensor (CDT) of the lowest singlet and triplet states of the metallocenothiaporphyrins, where the metal is V, Cr, Mn, Fe, Co, Ni, Mo, Tc, Ru, or Rh, have been studied with the gauge-including magnetically induced currents (GIMIC) method. The compounds containing V, Mn, Co, Tc or Rh were studied as cations because the neutral molecules have an odd number of electrons. The calculations show that the aromatic nature of most of the studied molecules follows the Huckel and Baird rules of aromaticity. CDT calculations on the high-spin states of the neutral metallocenothiaporphyrins with V, Mn, Co, Tc or Rh also shows that these molecules follow a unified extended Huckel and Baird aromaticity orbital-count rule stating that molecules with an odd number of occupied conjugated valence orbitals are aromatic, whereas molecules with an even number of occupied conjugated orbitals are antiaromatic.
  • Zippel, Christoph; Israil, Roumany; Schüssler, Lars; Hassan, Zahid; Schneider, Erik K.; Weis, Patrick; Nieger, Martin; Bizzarri, Claudia; Kappes, Manfred M.; Riehn, Christoph; Diller, Rolf; Braese, Stefan (2021)
    The modular synthesis of Au(I)/Ru(II) decorated mono- and heterobimetallic complexes with pi-conjugated [2.2]paracyclophane is described. [2.2]Paracyclophane serves as a rigid spacer which holds the metal centers in precise spatial orientations and allows metal-to-metal distance modulation. A broad set of architectural arrangements of pseudo -geminal, -ortho, -meta, and -para substitution patterns were employed. Metal-to-metal distance modulation of Au(I)/Ru(II) heterobimetallic complexes and the innate transannular pi-communication of the cyclophanyl scaffold provides a promising platform for the investigations of structure-activity relationship and cooperative effects. The Au(I)/Ru(II) heterobimetallic cyclophanyl complexes are stable, easily accessible, and exhibit promising catalytic activity in the visible-light promoted arylative Meyer-Schuster rearrangement.
  • Bizzarri, Claudia; Arndt, Andreas P.; Kohaut, Stephan; Fink, Karin; Nieger, Martin (2018)
    A mononuclear and two dinuclear heteroleptic Cu(I) complexes have been successfully prepared, using the chelating bis [(2-diphenylphosphino)phenyl] ether (DPEPhos) and pyrid-2'-yl-1H-1,2,3-triazole as chelating ligands. They show good luminescence in solution at room temperature with long-lived excited states. Furthermore, bimolecular quenching experiments of these new complexes with the catalyst Ni(cyclam)Cl-2 encourage the use of such compounds as photosensitizers for the photoreduction of carbon dioxide. (C) 2018 Elsevier B.V. All rights reserved.
  • Grupe, Merten; Boden, Pit; Di Martino-Fumo, Patrick; Gui, Xin; Bruschi, Cecilia; Israil, Roumany; Schmitt, Marcel; Nieger, Martin; Gerhards, Markus; Klopper, Wim; Riehn, Christoph; Bizzarri, Claudia; Diller, Rolf (2021)
    Chemical and spectroscopic characterization of the mononuclear photosensitizers [(DPEPhos)Cu(I)(MPyrT)](0/+) (CuL, CuLH) and their dinuclear analogues (Cu2L', Cu2L'H-2), backed by (TD)DFT and high-level GW-Bethe-Salpeter equation calculations, exemplifies the complex influence of charge, nuclearity and structural flexibility on UV-induced photophysical pathways. Ultrafast transient absorption and step-scan FTIR spectroscopy reveal flattening distortion in the triplet state of CuLH as controlled by charge, which also appears to have a large impact on the symmetry of the long-lived triplet states in Cu2L' and Cu2L'H-2. Time-resolved luminescence spectroscopy (solid state), supported by transient photodissociation spectroscopy (gas phase), confirm a lifetime of some tens of mu s for the respective triplet states, as well as the energetics of thermally activated delayed luminescence, both being essential parameters for application of these materials based on earth-abundant copper in photocatalysis and luminescent devices.