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Instruments / Technical Area	Publication Details	Published
I07-Surface & interface diffraction	Vacancy control in acene blends links exothermic singlet fission to coherence Clemens Zeiser , Chad Cruz , David R. Reichman , Michael Seitz , Jan Hagenlocher , Eric L. Chronister , Christopher J. Bardeen , Roel Tempelaar , Katharina Broch Nature Communications 12 DOI: 10.1038/s41467-021-25395-9 Diamond Proposal Number(s): [21899] Open Access Show Abstract ▼ Abstract: The fission of singlet excitons into triplet pairs in organic materials holds great technological promise, but the rational application of this phenomenon is hampered by a lack of understanding of its complex photophysics. Here, we use the controlled introduction of vacancies by means of spacer molecules in tetracene and pentacene thin films as a tuning parameter complementing experimental observables to identify the operating principles of different singlet fission pathways. Time-resolved spectroscopic measurements in combination with microscopic modelling enables us to demonstrate distinct scenarios, resulting from different singlet-to-triplet pair energy alignments. For pentacene, where fission is exothermic, coherent mixing between the photoexcited singlet and triplet-pair states is promoted by vibronic resonances, which drives the fission process with little sensitivity to the vacancy concentration. Such vibronic resonances do not occur for endothermic materials such as tetracene, for which we find fission to be fully incoherent; a process that is shown to slow down with increasing vacancy concentration.	Aug 2021
I07-Surface & interface diffraction	Photophysics of charge transfer complexes formed by tetracene and strong acceptors Christoph P. Theurer , Ana M. Valencia , Julian Hausch , Clemens Zeiser , Vipilan Sivanesan , Caterina Cocchi , Petra Tegeder , Katharina Broch The Journal Of Physical Chemistry C DOI: 10.1021/acs.jpcc.0c10815 Diamond Proposal Number(s): [21899] Show Abstract ▼ Abstract: Organic charge transfer complexes (CTCs) with near-infrared absorption received growing interest in the past years, but the details of their photophysics, especially in thin films, remain largely unknown. We combined experimental and computational methods to thoroughly investigate and compare CTCs formed by tetracene with 2,2′-(perfluoronaphthalene-2,6-diylidene)dimalononitrile and 2,3,5,6-tetrafluoro-7,7,8,8,-tetracyanoquinodimethane, respectively. Using ultrafast transient absorption spectroscopy, the photophysics of these small bandgap CTCs was revealed, which is dominated by a sub-picosecond relaxation of the excitons back to the ground state. In equimolar blends, tetracene singlet fission is suppressed while in blends with excess of tetracene reduced lifetimes of tetracene, singlet and triplet excitons were found.	Mar 2021
I07-Surface & interface diffraction	Thin film texture and optical properties of donor:acceptor complexes. Diindenoperylene:F6TCNNQ vs Alpha-Sexithiophene:F6TCNNQ Giuliano Duva , Linus Pithan , Clemens Zeiser , Berthold Reisz , Johannes Dieterle , Bernd Hofferberth , Paul Beyer , Laura Bogula , Andreas Opitz , Stefan Kowarik , Alexander Hinderhofer , Alexander Gerlach , Frank Schreiber The Journal Of Physical Chemistry C DOI: 10.1021/acs.jpcc.8b03744 Show Abstract ▼ Abstract: In this work two novel donor:acceptor (D:A) complexes, namely diindenoperylene(DIP):1,3,4,5,7,8-hexafluoro-tetracyanonaphthoquinodimethane(F6TCNNQ) and alpha-sexithiophene(6T):F6TCNNQ, are studied. The D:A complexes segregate in form of π-π stacked D:A co-crystals and can be observed by X-ray scattering. The different conformational degrees of freedom of the donor molecules, respectively, seem to affect the thin film crystalline texture and composition of the D:A mixtures significantly. In equimolar mixtures, for DIP:F6TCNNQ the crystallites are mostly uniaxially oriented and homogeneous, whereas for 6T:F6TCNNQ a mostly 3D (isotropic) orientation of the crystallites and coexistence of domains of pristine compounds and D:A complex, respectively, are observed. Using optical absorption spectroscopy we observe for each of the two mixed systems a set of new, strong transitions located in the near-IR range below the gap of the pristine compounds: such transitions are related to charge-transfer (CT) interactions between donor and acceptor. The optical anisotropy of domains of the D:A complexes with associated new electronic states is studied by ellipsometry. We infer that the CT-related transition dipole moment is perpendicular to the respective π-conjugated planes in the D:A complex.	Jul 2018

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