Format and motivation
1. Short term research stay for young as well as established researchers
2. Mobility for the preparation of joint research proposals
This proposal project aims at fostering and further sustain the recently initiated interdisciplinary cooperation between the research groups of Prof. Elena Grachova (Institute of Chemistry SPU) and Prof. Dr. Christian Müller (Institute of Chemistry and Biochemistry FUB). The general idea and the global goal of the project is the development of a new generation of technologically significant coordination compounds, having specific functional properties, which are controlled by the composition, structure and electronic characteristics of their components.
The first contact between Prof. Elena Grachova and Prof. Dr. Christian Müller was established during a series of public lectures organized by the German-Russian Interdisciplinary Scientific Center (G-RISC), the German House of Science and Innovation (DWIH), and the German Academic Exchange Service (DAAD) in June 2019 in St. Petersburg.
After then, a fruitful scientific discussion about the possibility to apply phosphinine-based ligands in the design and application of novel luminescent transition metal complexes has been followed by an invited lecture of Prof. E. Grachova during a visit at FUB in October 2019 and research visit of A. Paderina (post-graduate student from SPU) at FUB in June 2021 with support of the German-Russian Interdisciplinary Science Center (G-RISC). During this visit, the first promising experimental results have been obtained and a joint publication is currently in progress.

Plan and goal of the proposed activity
The design and development of novel organoelement compounds (here: ligands) and the application of their respective transition metal complexes (TMCs) as highly efficient molecular emitters in the field of optoelectronics (such as OLEDs), is one of the principal trends in modern coordination and material chemistry. The exponential growth of technologies using such compounds requests the continuous search for new systems with controlled properties. However, it must be conceded, that the currently known pool of classical ligands for luminescent TMCs is close to exhaustion. Consequently, the development of luminescent TMCs based on novel organoelement compounds is of fundamental importance, also with respect to the design of energy-efficient electroluminescent devices and sustainable lighting in the future.
From a fundamental and conceptual point of view, the design and synthesis of novel luminescent TMCs based on polydentate phosphinine ligands is the main topic addressed in this proposal. Phosphinines are a class of organophosphorus compounds exhibiting unusual donor-acceptor properties. Polydentate phosphinines possess a range of coordination modes and are therefore particularly versatile for the construction of novel transition metal complexes. Recent attempts to stabilize transition metal centers in medium to high oxidation states by chelating phosphinines have led to the development of a new range of complexes with potential applicability in single-molecule-based materials. Although phosphinines appear as very promising ligands due to their rich and flexible electronic and steric properties, these phosphorus heterocycles have not been widely used for the design of emissive molecules and materials. For now this field is limited by only a few fragmentary examples, with Prof. Dr. Christian Müller as one of the first pioneers in this field (see picture to the right).
Within the framework of this project and for the anticipated long-term mission, TMCs composed of heavy transition metals (Ir(III), Pt(II), Cu(I), Zn(II), Ln(III)) and phosphinine-based ligands, that contain an additional nitrogen functionality (bidentate P,N-hybrid ligands), are in the center of the investigations. These TMCs are luminescent upon excitation in the UV-Vis region due to metal-to-ligand energy transfer or due to the activation of intraligand energy transfer caused by a heavy atom effect.
The project consists of (a) the synthesis and complete characterization of novel phosphinine-based TMCs (Ir(III), Pt(II), Cu(I), Zn(II), Eu(III)) using X-ray crystallography, NMR- and FTIR spectroscopy, mass spectrometry and elemental analysis and (b) a comprehensive investigation of their photophysical properties. The results will not only be of quantitative (the development of a set of new coordination compounds with unique properties) but also of qualitative nature (new knowledge in the field of chemistry and photonics of TMCs based on phosphinines) with valuable contributions to chemistry and materials science.

Envisaged synergies between FUB and SPU
The key aspect of the project is the combination of a complementary expertise of the two research groups: the design, synthesis and characterization of the required phosphorus-based ligands and transition metal complexes (Prof. Dr. Christian Müller) and the design and photophysical characterization of the novel molecular emitters (Prof. Elena Grachova). The principal investigators are highly distinguished in their respective research fields. All the relevant resources, which are necessary for the synthesis and characterization of the new organophosphorus compounds and TMCs are available at FUB, while the highly important equipment and experience for the detailed measurement of the optoelectronic properties of the TMCs is available at SPU. This partnership will provide a very visible and highly representative sign for the alliance between Berlin and St. Petersburg.
The proposed project is in line with the main trends of modern organoelement and coordination chemistry. The use of new ligands (in this case phosphinines) for the construction of molecular materials with desired properties (luminescent complexes of transition metals) will allow to make the next step to real ‘smart’ materials and will contribute to the development of modern and future technologies based on the generation of radiation in the sunlight wavelength range.
In the framework of the proposed collaborative research, the methods for the directed and controlled synthesis and characterization of phosphinine-based ligands and their respective TMCs will be developed. In the future, the second fundamental question of the project will be addressed, which is related to a detailed study of the key factors that determine the photophysical behavior of the novel functional luminophores.

Concreteness of future joint research
Since the interdisciplinary cooperation between the research groups of Prof. Elena Grachova and Prof. Dr. Christian Müller was started, the first phosphinine-based coordination compounds of Cu(I) have been prepared and structurally characterized. These complexes demonstrate bright photoluminescence upon irradiation with UV-light at room temperature with sufficient red shift of the energy comparing with diimine-based analogies. Moreover, the phosphinine-based complexes of Cu(I) are TADF (thermally activated delayed fluorescence) emitters that makes them promising objects to create a real OLED material. This preliminary result of the joint project nicely demonstrates the proof of concept. A detailed investigation on the photophysical properties of these novel TMCs is currently curried out and a joint publication is in progress.

Compatibility of the FUB/SPU research profiles
This proposal fosters the recently initiated interdisciplinary cooperation between the leading research groups of the Institute of Chemistry at SPU and the Institute of Chemistry and Biochemistry at FUB in the fields of organoelement chemistry, coordination chemistry and photonics of luminescent transition metal complexes. The research expertise (vide infra) of the principle investigators are complementary and are perfectly compatible with the FUB/SPU research profiles. Prof. Elena Grachova and Prof. Dr. Christian Müller are internationally highly reputed and have more than 15 years experience in their respective research fields.

Future funding beyond the initial phase
To further strengthen and to support the envisaged long-term cooperation between the two groups further funding will be attracted from several sources (see graphic below). Prof. Elena Grachova is a Humboldt alumni and can apply for the Humboldt alumni-research group linkage program. It is designed to foster a sustainable basis for long-term international academic collaboration between alumni of Alexander von Humboldt Foundation programs abroad and academics in Germany. Joint research projects can be sponsored with a funding amount of up to € 55,000 over a period of up to three years. The funding may be used to finance reciprocal research visits, conferences and workshops and consumables. The RSF-DFG program facilitates the support of collaborative work between German and Russian research groups for the funding period 2022–2024 in all fields of science. The German Academic exchange programs (DAAD) support short-term visits by researchers and students to Berlin and St. Petersburg.