NEWS
19.07.2019

Decision in the German Excellence Strategy

The Berlin University Alliance has won funding as a group in the Universities of Excellence funding line of the German federal and state governments’ Excellence Strategy. The German Council of Science and Humanities announced the decision on July 19, 2019, in Bonn. The four Berlin partners – Freie Universität Berlin, Humboldt-Universität zu Berlin, Technische Universität Berlin, and Charité – Universitätsmedizin Berlin – submitted a joint proposal entitled Crossing Boundaries toward an Integrated Research Environment and in a highly competitive process were able to convince the reviewers of its feasibility.

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19.07.2019

Article of IRIS junior research group leader Michael J. Bojdys published in Nature Communications

The IRIS junior research group leader Michael J. Bojdys and his international team have achieved a great success: Their article “Real-time optical and electronic sensing with a β-amino enone linked, triazine-containing 2D covalent organic framework” has been selected to be published in the renowned journal Nature Communications.
Bojdys article deals with aromatic two-dimensional covalent organic frameworks (2D COFs), which are a class of porous polymers that allow the precise incorporation of organic units into periodic structures.COFs can be chemically designed to incorporate particular surface functional groups which can be exploited to tune the optical and electronic properties. However, low stability towards chemical triggers has hampered their practical implementations.
Together with a team from the Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences (Prague, Czech Republic), IRIS junior research group leader Michael J. Bojdys and his team from Humboldt-Universität zu Berlin have explored a new design principle for COFs that makes use of strong, overall conjugation and incorporation of donor-acceptor domains. In this study a new, a highly stable chemoresistant β-amino enone linked, triazine-containing COF was used as a real-time, reversible optical and electronic sensor for volatile acids and bases. The team was further able to conclude that the sensing capabilities of the COF was achieved by preferential protonation
of the electron accepotor – a triazine ring in the structure – , resulting in an optical response visible to the naked eye and an increase of bulk electrical conductivity by two orders of magnitude. These findings demonstrate a powerful approach to design more practical sensors and switches, and take genuine advantage of the chemoresistant make-up, porous structure, and overall conjugation of fully-aromatic systems.
IRIS Adlershof would like to congratulate Michael J. Bojdys and his team on this successful study and its publication in Nature Communications!
Due to his great enthusiasm for the concept of IRIS Adlershof and the research carried out here, ERC-grant holder Bojdys joined the Humboldt-Universität zu Berlin and IRIS Adlershof in 2018 as leader of the junior research group “Functional Materials”. The group’s research aims at the development of metal-free, electronic components for transistors and sensors on the basis of functional materials made up of light, covalently-bonded atoms. At the heart of the project lies the challenge to transfer the control mechanisms and modularity known from molecular, organic chemistry to macroscopic structures.

Real-time optical and and electronic sensing with a β-amino enone linked, triazine-containing 2D covalent organic framework
R. Kulkarni, Y. Noda, D.K Barange, Y.S. Kochergin, P. Lyu, B. Balcarov, P. Nachtigall, and M.J. Bojdys
Nat. Commun 10 (2019) 3228


Click here for the press release of the Humboldt-Universität zu Berlin!

05.06.2019

Organic electronics: a novel semiconductor from the family of carbon nitrides

Research teams from the Humboldt-Universität and the Helmholtz Zentrum Berlin (HZB) have investigated a new material from the family of carbon nitrides. Triazine-based graphitic carbon nitride (TGCN) is a semiconductor that is useful in optoelectronic applications. Its structure is two-dimensional and layered, and it resembles that of graphene. Unlike graphene, its conductivity between the layers is 65-times higher than in-plane.

Some organic materials can be used in optoelectronics just like silicon-based semiconductors. Whether in solar cells, light-emitting diodes, or as transistors – the important property is the bandgap, i.e. the energy-difference of the electrons in the valence band and the conduction band. The basic principle underlying all electronic components is that electrons can be promoted by light or by voltage between the valence and the conduction band. Here, bandgaps between 1 and 2 eV are ideal.

A team led by the chemist Dr. Michael J. Bojdys from the chemistry department and IRIS Adlershof of the Humboldt-Universität zu Berlin, has recently synthesized an organic semiconductor from the family of carbon nitrides. This triazine-based graphitic carbon nitride (TGCN) consists exclusively from carbon and nitrogen atoms and can be grown as a brown film on quartz glass substrates. The C- and N-atoms connect in hexagonal, honeycomb patterns like carbon atoms in graphene. Just like in graphene, the crystal structure of TGCN is based on layered, two-dimensional sheets. In graphene, in-plane conductivity is excellent, however, it is much lower through the planes. In the case of TGCN, the opposite is observed: through-plane conductivity is 65-times higher than in-plane. With a bandgap of 1.7 eV TGCN is a good candidate for optoelectronic applications.

The HZB-physicist Dr. Christoph Merschjann has examined the charge carrier transport in samples of TGCN using time-resolved absorption measurements in the femto- to nanosecond regime at the laser lab JULiq – a joint lab between the HZB and the Freie Universität Berlin. Such laser experiments offer a unique way to correlate macroscopic conductivity and microscopic transport models. From his measurements, he was able to deduce how the charge carriers diffuse throughout the material. “Electrons do not exit the hexagonal honeycombs of triazine units horizontally, but they move at a slope to the nearest triazine-unit in the neighboring layer. The crystal structure of the material leads to a preferred movement of charge carriers along tube-like channels.” This mechanism could explain why the conductivity of TGCN is fundamentally higher through-plane than in-plane. “TGCN is the hitherto best candidate to replace silicon semiconductors and the critical, rare-earth dopants used in their manufacture”, says Michael Bojdys. “The production method for TGCN that we developed in my group at the Humboldt-Universität zu Berlin yields flat layers of semiconducting TGCN on insulating quartz glass. This enables relatively easy upscaling and device production.”

These results were recently published in the international edition of the renowned journal "Angewandte Chemie".