Interfacial synthesis of novel phthalocyanine dyes – Publication by A4 (Gottfried), A6 (Tonner) & A7 (Sundermeyer)

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In their study published in Nature Communications, the authors from three SFB-projects with expertise in interface chemistry, organometallic synthesis, and theoretical chemistry, jointly publish their research into template-controlled interfacial synthesis of unprecedented extended phthalocyanine dyes.

Interfacial template approach: control over the topology of the reaction products is achieved by using differently-sized metal templates in 2D confinement. (after publication-Fig. 1) Copyright by CC-BY 4.0.

Phthalocyanines possess unique optical and electronic properties and thus are widely used in (opto)electronic devices, coatings, photodynamic therapy, etc. Extending the π-conjugation of phthalocyanine dyes, while synthetically challenging, has the potential to produce desirable new molecular materials.

Here, Dr. Qitang Fan and coworkers use a templated interface approach to synthesize several extended phthalocyanine derivatives from the same building block, including an unprecedented lanthanide superphthalocyanine and an open-chain polycyanine (fig. left). The former represents the first superphthalocyanine without uranium center, while the latter provides an intriguing model for an organic semiconducting polymer with an absorption band in the visible range. Detailed study of these new materials by scanning tunneling microscopy, photoemission spectroscopy, and density functional theory calculations (fig. below), reveal their chemical structure and mechanical as well as electronic properties.

Orbitals: Lowest unoccupied molecular orbitals of Fe-NPc and Gd-SNPc, lowest unoccupied crystal orbital of polycyanine, from density-functional theory calculation. Copyright by CC-BY 4.0. 

See also natureresearch’s “Behind The Paper”-contribution by Michael Gottfried on “Synthesis in flatland: rings and chains grown on surfaces”.

Publication

Q. Fan, J.-N. Luy, M. Liebold, K. Greulich, M. Zugermeier, J. Sundermeyer, R. Tonner, J.M. Gottfried, Template‐controlled on‐surface synthesis of a lanthanide supernaphthalocyanine and its open‐chain polycyanine counterpart, Nature Commun. 10 (2019) 5049 DOI:s41467-019-13030-7

Contact

Prof. Dr. Michael Gottfried
Philipps-Universität Marburg
SFB 1083 project A4
Tel.: 06421 28 22541
EMAIL

Metal chalcogenide clusters on doped TMDC-layers – Publication by A9 (Dehnen) & A6 (Tonner)

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In their study published in the Journal of the American Chemical Society, Eike Dornsiepen, Fabian Pieck, Ralf Tonner, and Stefanie Dehnen report on the synthesis of molecular model systems for the up to now unknown adsorption of organotin chalcogenide cluster molecules on TMDC surfaces. Computational studies reveal similar covalent bonding interactions for the model system as well as for the adsorption on a TMDC surface.

Reprinted with permission from Journal of the American Chemical, 2019, 141,41, 16494-16500.

Transition metal dichalcogenides (TMDCs) like MoS2 or WS2 have gained large interest for their potential in electronic applications. Combinations with other 2D materials in heterostructures have already been demonstrated as useful in various devices, such as tunneling transistors or solar cells. Hybrid systems combining 2D materials with layers of adsorbed molecules have proven to be interesting for optoelectronic applications, as they allow for tailoring of electronic properties and high photoabsorption of molecular materials. In most of these studies, the adsorbed molecules were organic molecules like pentacene or coordination compounds like phthalocyanines, which interacted with the surface by means of dispersion interactions. The interaction of larger organometallic systems with TMDCs, however, has not yet been studied. This is in part due to the fact that the chemisorption of molecules on TMDC surfaces is relatively weak, hence adsorbents tend to move randomly around.

With the aim to mimic the yet unknown covalent deposition of metal chalcogenide clusters on transition metal dichalcogenide MoS2 or WS2 layers, and thereby explore the interaction between the two systems and potential consequences for the physical properties of the TMDC material, the authors synthesized heterobimetallic model systems. The heterocubane-type cluster [(SnCl3) WCp)3S4], the organotin-sulfidomolybdate cluster [{(PhSn)3SnS6}{(MoCp)3S4}], and the corresponding tungstate [(PhSn)3SnS6{(WCp)3S4}] were obtained in ligand exchange reactions from [(PhSn)4S6] and [M(CO)3CpCl] (with M = Mo, W). Indeed, the {M3S4} cages in the three compounds resemble a section of the respective TMDC monolayers, altogether representing minimal molecular model systems for the adsorption of organotin sulfide clusters on MoS2 or WS2. The interaction between the {(MCp)3S4} and {(PhSn)3SnS6} subunits is characterized by multicenter bonding, rendering the respective Sn atom as Sn(II), hence driving the clusters into a mixed-valence Sn(IV)/Sn(II) situation, and the M atoms as M(IV) upon an in situ redox process. The attachment is thus weaker than via regular covalent M-S bonds, but definitely stronger than via van der Waals interactions that have been characteristic for all known interactions of clusters on TMDC surfaces so far. Calculations of a periodic model system that simulates the attachment of the {(PhSn3S6} fragment to MS2 surfaces reveal striking similarities in structure and bonding situation, given the MS2 surfaces are doped with titanium or other electron-poor metal atoms. This renders the new compounds as relevant molecular models for covalent attachment of larger organometallic systems on TMDCs.

Publication

E. Dornsiepen, F. Pieck, R. Tonner, S. Dehnen, [{(PhSn)3SnS6}{(MCp)3S4}] (M = W, Mo): minimal molecular models of the covalent attachment of metal chalcogenide clusters on doped transition metal dichalcogenide layers, J. Am. Chem Soc. (2019) DOI: 10.1021/jacs.9b09209

Contact

Prof. Dr. Stefanie Dehnen
Philipps-Universität Marburg
SFB 1083 project A9
Tel.: 06421 28 25751
EMAIL

Growth of extended DNTT fibers on metal substrates by suppression of step-induced nucleation – Publication by A2 (Witte)

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In their study published in Nanoscale Horizons, Maximilan Dreher, Dayeon Kang, Tobias Breuer and Gregor Witte introduce and validate a new concept to suppress the defect-driven fiber nucleation at surface steps by selective blocking of the active step sites using small molecules, so that the formation of crystalline, organic fibers is only governed by the intrinsic epitaxial growth on ideal, defect-free surface regions.

DNTT fiber structures grown on Ag(111) substrates without (left) and with (right) pre-exposition of oxygen to the surface. The oxygen suppresses the DNTT molecules to adsorb at the step edges, which leads to straight, elongated and epitaxially aligned fibers. (Image: M. Dreher). Reproduced with permission from the Royal Society of Chemistry.

Due to their anisotropic optoelectronic properties, crystalline organic fibers constitute an interesting class of nanoscale materials with great potential for integration into future optoelectronic devices based on organic-inorganic hybrid systems. While chemical synthesis allows for flexible tailoring of electronic molecular properties, well-established structuring methods such as, e.g. lithography are hardly applicable to most molecular materials. Therefore, self-organization is an important alternative route for structuring molecular materials especially for organic/inorganic hybrid architectures. While molecular materials often form crystalline fibers, their length and orientation is, however, limited by surface defects such as steps of the supports that cannot be prevented even on very perfect, single crystalline substrates, hence drastically restricting their use in device applications.

In their study the authors analyzed the influence of surface step edges on the initial growth of fibers for the case of the high performing organic semi¬conductor dinaphthothienothiophene (DNTT) and developed a new concept to suppress the defect–driven fiber nucleation. Based on a comparison of the organic film growth on densely packed, flat noble metal surfaces and on a regularly stepped, vicinal surface, they first showed how substrate steps affect the azimuthal molecular orientation in the seed layer and also the subsequent fiber formation. In a next step they demonstrate that this parasitical step-induced fiber nucleation that occurs also on densely packed Ag(111) surfaces can be suppressed by first exposing the metal support to oxygen, or even briefly to ambient condition, which causes a selective saturation of the active step sites. They show that this not only leads to an exclusive growth of epitaxial DNTT fibers but also strongly increases the fiber size to several hundreds of microns. This novel approach is quite versatile and allows a distinct improvement of template assisted growth and thereby the quality of organic/inorganic hybrids.

Publication

M. Dreher, D. Kang, T. Breuer and G. Witte,
Growth of extended DNTT fibers on metal substrates by suppression of step-induced nucleation
Nanoscale Horizons (2019) DOI:10.1039/C9NH00422J

Poster Award
The paper’s first author Maximilian Dreher is currently a Master’s student within SFB-project A2. We congratulate him on receiving the prize for his poster on the above research which he presented at the Cecam Workshop on “Fabrication processes and molecular organization in organic thin films: Theory and simulation meet experiments” held in Lecco, Italy from July 17-20, 2019.

Contact

Prof. Dr. Gregor Witte
Philipps-Universität Marburg
SFB 1083 project A2
Tel.: 06421 28 21384
EMAIL