@article{MerzDietzVonhausenetal.2020,
  author    = {Merz, Julia and Dietz, Maximilian and Vonhausen, Yvonne and W{\"o}ber, Frederik and Friedrich, Alexandra and Sieh, Daniel and Krummenacher, Ivo and Braunschweig, Holger and Moos, Michael and Holzapfel, Marco and Lambert, Christoph and Marder, Todd B.},
  title     = {Synthesis, Photophysical and Electronic Properties of New Red-to-NIR Emitting Donor-Acceptor Pyrene Derivatives},
  series = {Chemistry - A European Journal},
  volume    = {26},
  journal   = {Chemistry - A European Journal},
  number    = {2},
  doi       = {10.1002/chem.201904219},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-207486},
  pages     = {438-453},
  year      = {2020},
  abstract  = {We synthesized new pyrene derivatives with strong bis(para -methoxyphenyl)amine donors at the 2,7-positions and n -azaacene acceptors at the K-region of pyrene. The compounds possess a strong intramolecular charge transfer, leading to unusual properties such as emission in the red to NIR region (700 nm), which has not been reported before for monomeric pyrenes. Detailed photophysical studies reveal very long intrinsic lifetimes of >100 ns for the new compounds, which is typical for 2,7-substituted pyrenes but not for K-region substituted pyrenes. The incorporation of strong donors and acceptors leads to very low reduction and oxidation potentials, and spectroelectrochemical studies show that the compounds are on the borderline between localized Robin-Day class-II and delocalized Robin-Day class-III species.},
  language  = {en}
}
@article{HattoriMichailSchmiedeletal.2019,
  author    = {Hattori, Yohei and Michail, Evripidis and Schmiedel, Alexander and Moos, Michael and Holzapfel, Marco and Krummenacher, Ivo and Braunschweig, Holger and M{\"u}ller, Ulrich and Pflaum, Jens and Lambert, Christoph},
  title     = {Luminescent Mono-, Di-, and Tri-radicals: Bridging Polychlorinated Triarylmethyl Radicals by Triarylamines and Triarylboranes},
  series = {Chemistry - A European Journal},
  volume    = {25},
  journal   = {Chemistry - A European Journal},
  number    = {68},
  doi       = {10.1002/chem.201903007},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-208162},
  pages     = {15463-15471},
  year      = {2019},
  abstract  = {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.},
  language  = {en}
}
@article{MieczkowskiSteinmetzgerBessietal.2021,
  author    = {Mieczkowski, Mateusz and Steinmetzger, Christian and Bessi, Irene and Lenz, Ann-Kathrin and Schmiedel, Alexander and Holzapfel, Marco and Lambert, Christoph and Pena, Vladimir and H{\"o}bartner, Claudia},
  title     = {Large Stokes shift fluorescence activation in an RNA aptamer by intermolecular proton transfer to guanine},
  series = {Nature Communications},
  volume    = {12},
  journal   = {Nature Communications},
  doi       = {10.1038/s41467-021-23932-0},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-254527},
  pages     = {3549},
  year      = {2021},
  abstract  = {Fluorogenic RNA aptamers are synthetic functional RNAs that specifically bind and activate conditional fluorophores. The Chili RNA aptamer mimics large Stokes shift fluorescent proteins and exhibits high affinity for 3,5-dimethoxy-4-hydroxybenzylidene imidazolone (DMHBI) derivatives to elicit green or red fluorescence emission. Here, we elucidate the structural and mechanistic basis of fluorescence activation by crystallography and time-resolved optical spectroscopy. Two co-crystal structures of the Chili RNA with positively charged DMHBO+ and DMHBI+ ligands revealed a G-quadruplex and a trans-sugar-sugar edge G:G base pair that immobilize the ligand by π-π stacking. A Watson-Crick G:C base pair in the fluorophore binding site establishes a short hydrogen bond between the N7 of guanine and the phenolic OH of the ligand. Ultrafast excited state proton transfer (ESPT) from the neutral chromophore to the RNA was found with a time constant of 130 fs and revealed the mode of action of the large Stokes shift fluorogenic RNA aptamer.},
  language  = {en}
}
@article{TurkinHolzapfelAgarwaletal.2021,
  author    = {Turkin, Arthur and Holzapfel, Marco and Agarwal, Mohit and Fischermeier, David and Mitric, Roland and Schweins, Ralf and Gr{\"o}hns, Franziska and Lambert, Christoph},
  title     = {Solvent Induced Helix Folding of Defined Indolenine Squaraine Oligomers},
  series = {Chemistry—A European Journal},
  volume    = {27},
  journal   = {Chemistry—A European Journal},
  number    = {32},
  doi       = {10.1002/chem.202101063},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256869},
  pages     = {8380-8389},
  year      = {2021},
  abstract  = {A protecting group strategy was employed to synthesise a series of indolenine squaraine dye oligomers up to the nonamer. The longer oligomers show a distinct solvent dependence of the absorption spectra, that is, either a strong blue shift or a strong red shift of the lowest energy bands in the near infrared spectral region. This behaviour is explained by exciton coupling theory as being due to H- or J-type coupling of transition moments. The H-type coupling is a consequence of a helix folding in solvents with a small Hansen dispersity index. DOSY NMR, small angle neutron scattering (SANS), quantum chemical and force field calculations agree upon a helix structure with an unusually large pitch and open voids that are filled with solvent molecules, thereby forming a kind of clathrate. The thermodynamic parameters of the folding process were determined by temperature dependent optical absorption spectra.},
  language  = {en}
}
@article{BoldStolteShoyamaetal.2022,
  author    = {Bold, Kevin and Stolte, Matthias and Shoyama, Kazutaka and Holzapfel, Marco and Schmiedel, Alexander and Lambert, Christoph and W{\"u}rthner, Frank},
  title     = {Macrocyclic donor-acceptor dyads composed of a perylene bisimide dye surrounded by oligothiophene bridges},
  series = {Angewandte Chemie Internationale Edition},
  volume    = {61},
  journal   = {Angewandte Chemie Internationale Edition},
  number    = {1},
  doi       = {10.1002/anie.202113598},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256569},
  year      = {2022},
  abstract  = {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 F{\"o}rster Resonance Energy Transfer and photoinduced electron transfer, thereby leading to extremely low fluorescence quantum yields even in the lowest polarity cyclohexane solvent.},
  language  = {en}
}
@article{MieczkowskiSteinmetzgerBessietal.2021,
  author    = {Mieczkowski, Mateusz and Steinmetzger, Christian and Bessi, Irene and Lenz, Ann-Kathrin and Schmiedel, Alexander and Holzapfel, Marco and Lambert, Christoph and Pena, Vladimir and H{\"o}bartner, Claudia},
  title     = {Large Stokes shift fluorescence activation in an RNA aptamer by intermolecular proton transfer to guanine},
  series = {Nature Communications},
  volume    = {12},
  journal   = {Nature Communications},
  doi       = {10.1038/s41467-021-23932-0},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-270274},
  year      = {2021},
  abstract  = {Fluorogenic RNA aptamers are synthetic functional RNAs that specifically bind and activate conditional fluorophores. The Chili RNA aptamer mimics large Stokes shift fluorescent proteins and exhibits high affinity for 3,5-dimethoxy-4-hydroxybenzylidene imidazolone (DMHBI) derivatives to elicit green or red fluorescence emission. Here, we elucidate the structural and mechanistic basis of fluorescence activation by crystallography and time-resolved optical spectroscopy. Two co-crystal structures of the Chili RNA with positively charged DMHBO+ and DMHBI+ ligands revealed a G-quadruplex and a trans-sugar-sugar edge G:G base pair that immobilize the ligand by π-π stacking. A Watson-Crick G:C base pair in the fluorophore binding site establishes a short hydrogen bond between the N7 of guanine and the phenolic OH of the ligand. Ultrafast excited state proton transfer (ESPT) from the neutral chromophore to the RNA was found with a time constant of 130 fs and revealed the mode of action of the large Stokes shift fluorogenic RNA aptamer.},
  language  = {en}
}
@article{BoldStolteShoyamaetal.2022,
  author    = {Bold, Kevin and Stolte, Matthias and Shoyama, Kazutaka and Krause, Ana-Maria and Schmiedel, Alexander and Holzapfel, Marco and Lambert, Christoph and W{\"u}rthner, Frank},
  title     = {Macrocyclic Donor-Acceptor Dyads Composed of Oligothiophene Half-Cycles and Perylene Bisimides},
  series = {Chemistry - A European Journal},
  volume    = {28},
  journal   = {Chemistry - A European Journal},
  number    = {30},
  doi       = {10.1002/chem.202200355},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-276435},
  year      = {2022},
  abstract  = {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.},
  language  = {en}
}