TY - JOUR A1 - Bold, Kevin A1 - Stolte, Matthias A1 - Shoyama, Kazutaka A1 - Krause, Ana‐Maria A1 - Schmiedel, Alexander A1 - Holzapfel, Marco A1 - Lambert, Christoph A1 - Würthner, Frank T1 - Macrocyclic Donor‐Acceptor Dyads Composed of Oligothiophene Half‐Cycles and Perylene Bisimides JF - Chemistry – A European Journal N2 - A series of donor‐acceptor (D−A) macrocyclic dyads consisting of an electron‐poor perylene bisimide (PBI) π‐scaffold bridged with electron‐rich α‐oligothiophenes bearing four, five, six and seven thiophene units between the two phenyl‐imide substituents has been synthesized and characterized by steady‐state UV/Vis absorption and fluorescence spectroscopy, cyclic and differential pulse voltammetry as well as transient absorption spectroscopy. Tying the oligothiophene strands in a conformationally fixed macrocyclic arrangement leads to a more rigid π‐scaffold with vibronic fine structure in the respective absorption spectra. Electrochemical analysis disclosed charged state properties in solution which are strongly dependent on the degree of rigidification within the individual macrocycle. Investigation of the excited state dynamics revealed an oligothiophene bridge size‐dependent fast charge transfer process for the macrocyclic dyads upon PBI subunit excitation. KW - donor-acceptor dyad KW - macrocycle KW - oligothiophene KW - perylene bisimide KW - photoinduced electron transfer Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-276435 VL - 28 IS - 30 ER - TY - JOUR A1 - Bold, Kevin A1 - Stolte, Matthias A1 - Shoyama, Kazutaka A1 - Holzapfel, Marco A1 - Schmiedel, Alexander A1 - Lambert, Christoph A1 - Würthner, Frank T1 - Macrocyclic donor-acceptor dyads composed of a perylene bisimide dye surrounded by oligothiophene bridges JF - Angewandte Chemie Internationale Edition N2 - Two macrocyclic architectures comprising oligothiophene strands that connect the imide positions of a perylene bisimide (PBI) dye have been synthesized via a platinum-mediated cross-coupling strategy. The crystal structure of the double bridged PBI reveals all syn-arranged thiophene units that completely enclose the planar PBI chromophore via a 12-membered macrocycle. The target structures were characterized by steady-state UV/Vis absorption, fluorescence and transient absorption spectroscopy, as well as cyclic and differential pulse voltammetry. Both donor–acceptor dyads show ultrafast Förster Resonance Energy Transfer and photoinduced electron transfer, thereby leading to extremely low fluorescence quantum yields even in the lowest polarity cyclohexane solvent. KW - organic chemistry KW - photoinduced electron transfer KW - donor–acceptor dyads KW - macrocycles KW - oligothiophenes KW - perylenebisimide Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256569 VL - 61 IS - 1 ER - TY - JOUR A1 - Spenst, Peter A1 - Young, Ryan M. A1 - Wasielewski, Michael R. A1 - Würthner, Frank T1 - Guest and solvent modulated photo-driven charge separation and triplet generation in a perylene bisimide cyclophane JF - Chemical Science N2 - Cofacial positioning of two perylene bisimide (PBI) chromophores at a distance of 6.5 angstrom in a cyclophane structure prohibits the otherwise common excimer formation and directs photoexcited singlet state relaxation towards intramolecular symmetry-breaking charge separation (τ\(_{CS}\) = 161 +/- 4 ps) in polar CH\(_2\)Cl\(_2\), which is thermodynamically favored with a Gibbs free energy of ΔG\(_{CS}\) = -0.32 eV. The charges then recombine slowly in τ\(_{CR}\) = 8.90 +/- 0.06 ns to form the PBI triplet excited state, which can be used subsequently to generate singlet oxygen in 27% quantum yield. This sequence of events is eliminated by dissolving the PBI cyclophane in non-polar toluene, where only excited singlet state decay occurs. In contrast, complexation of electron-rich aromatic hydrocarbons by the host PBI cyclophane followed by photoexcitation of PBI results in ultrafast electron transfer (<10 ps) from the guest to the PBI in CH\(_2\)Cl\(_2\). The rate constants for charge separation and recombination increase as the guest molecules become easier to oxidize, demonstrating that charge separation occurs close to the peak of the Marcus curve and the recombination lies far into the Marcus inverted region. KW - photoinduced electron transfer KW - Marcus inverted region KW - cyclic perylene bisimide KW - PBI cyclophane Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-191252 VL - 7 IS - 8 ER - TY - THES A1 - Klein, Johannes Hubert T1 - Electron Transfer and Spin Chemistry in Iridium-Dipyrrin Dyads and Triads T1 - Elektronentransfer und Spinchemie in Iridium-Dipyrrin-Dyaden und -Triaden N2 - The successful synthesis of a family of donor-iridium complex-acceptor triads (T1–T6, pMV1 and mMV1) and their electrochemical and photophysical properties were presented in this work. Triarylamines (TAA) were used as donors and naphthalene diimide (NDI) as acceptor. A bis-cyclometalated phenylpyrazole iridium dipyrrin complex acts as a photosensitiser. In addition, a molecular structure of T1 was obtained by single crystal X-ray diffraction. Transient absorption spectroscopy experiments of these triads resembled that upon excitation a photoinduced electron transfer efficiently generates long-lived, charge-separated (CS) states. Thereby, the electron-transfer mechanism depends on the excitation energy. The presence of singlet and triplet CS states was clarified by magnetic-field dependent transient-absorption spectroscopy in the nanosecond time regime. It was demonstrated that the magnetic field effect of charge-recombination kinetics showed for the first time a transition from the coherent to the incoherent spin-flip regime. The lifetime of the CS states could be drastically prolonged by varying the spacer between the iridium complex and the NDI unit by using a biphenyl instead of a phenylene unit in T4. A mixed-valence (MV) state of two TAA donors linked to an iridium metal centre were generated upon photoexcitation of triad pMV1 and mMV1. The mixed-valence character in these triads was proven by the analysis of an intervalence charge-transfer (IV-CT) band in the (near-infrared) NIR spectral region by femtosecond pump-probe experiments. These findings were supported by TD-DFT calculations. The synthesis of dyads (D1–D4) was performed. Thereby the dipyrrin ligand was substituted with electron withdrawing groups. The electrochemical and photophysical characterisation revealed that in one case (D4) it was possible to generate a CS state upon photoexcitation. N2 - In dieser Arbeit wurden die erfolgreiche Synthese einer Donor-Iridiumkomplex-Akzeptor-Familie (Triaden T1–T6, pMV1 und mMV1) und deren elektrochemischen und photophyiskalischen Eigenschaften vorgestellt. Als Donor wurden Triarylamine (TAA) verwendet, als Akzeptoreinheit diente ein Naphthalin-Diimid (NDI). Ein bis-cyclometallierter Phenylpyrazol-Iridium-Dipyrrin-Komplex übernahm die Aufgabe des Photosensibilisators. Die synthetischen Arbeiten konnten mit einer molekularen Struktur von T1 mittels Röntgenbeugung eines Einkristalls ergänzt werden. Bei Photoanregung der Triaden mit transienter Absorptions-Spektroskopie wurde die sehr effiziente Bildung von langlebigen, ladungsgetrennten (CS) Zuständen beobachtet. Es wurde zudem herausgefunden, dass der Elektronentransfer (ET)-Mechanismus von der verwendeten Anregungswellenlänge abhängt. Der Nachweis von Singulett und Triplett CS-Zuständen wurde mittels magnetfeldabhängiger, transienter Absorptions-Spektroskopie erbracht. Eine Analyse des Magnetfeldeffekts der Ladungsrekombinations-Kinetik zeigte zum ersten Mal einen Übergang von einem kohärenten zu einem inkohärenten Spinumkehrprozess. Die Lebenszeit des CS-Zustandes ließ sich dramatisch verlängern indem die Phenylen- durch eine Biphenyl-Brückeneinheit zwischen dem Iridiumkomplex und dem NDI ersetzt wurde. Gemischvalente Zustände konnten mittels photinduziertem Elektronentransfer in den Triaden pMV1 und mMV1 erzeugt werden. Im Fall von pMV1 wurde eine intensive Intervalenz-Ladungstransfer (IV-CT) Bande im nahinfraroten Spektralbereich mittels Femtosekunden transienter Anregungs-Abfrage-Spektroskopie beobachtet werden. Die Analyse dieser IV-CT Bande wurde mit TD-DFT Rechnungen vervollständigt. Die Synthese von Dyaden (D1–D4) wurde erfolgreich durchgeführt, dabei wurde der Dipyrrin-Ligand mit elektronenziehenden Substituenten versehen. Die spektroskopische und elektrochemische Analyse erbrachte nach erfolgter Lichtanregung in einem Fall (D4) ebenfalls einen CS-Zustand. KW - Elektronentransfer KW - Spin flip KW - Triad KW - Ladungstransfer KW - Photosensibilisator KW - photoinduced electron transfer KW - charge-separated state KW - spin chemistry KW - donor-photosensibilisator-acceptor triad KW - iridium complex KW - photoinduzierter Elektronentransfer KW - Spinchemie KW - Donor-Photosensibilisator-Akzeptor Triade KW - Iridiumkomplexe Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-118726 ER -