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Dendrimers for photonic devices

Final Report Summary - DPHOTOD (Dendrimers for photonic devices)

The chemistry teams of the DphotoD project synthesized more than thirty new compounds.
During the preparation procedures more than one hundred of precursors and semi-products have been also designed and then prepared in substantial quantities. Such work was possible only because of very extensive exchanges between chemists in Leuven (Belgium) and Ivanovo (Russia).
The family of the dendrimer compounds is represented by several series of molecules constructed by connecting carbazole-based dendrons of different sizes and geometries to the porphyrin core using different linkers. Metal-exchange reactions were found to be very effective for synthesis of complexes of meso-substituted porphyrins with metals of variable valence, which can find wide applications for designing of red-ox processes catalysts and photochromic materials.
Different optical spectroscopy methods were used to study the influence of the dendritic shell on the luminescence properties of the core. Our first task was to understand fundamental mechanisms of such influence and while the second task was to find conditions when such dendrimers can be used as molecular sensors.
We found that probably the most important factor that influences the optical properties is how the porphyrin core “feels” the dendritic shell is the attachment positions of the dendrons and the nature of the linkers – small molecular bridges - through which the dendrons are attached to the core molecule. The photophysics of the porphyrin core is strongly influenced by the nature of the dendrons and their connection via mechanical and electronic communication.
Signatures for the molecules flexibility and mechanical stress applied on the porphyrin core were established in fluorescence, infra-red and Raman spectra. These are important characterization methods which can be used both in fundamental and in applied science. Porphyrin dendrimers with very flexible dendritic shells are shown to be promising viscosity sensors at molecular scale.
By experimenting with different type of linkers between the porphyrin core and dendrons we found conditions for stabilization of mono-protonated form of porphyrin depending on the ability of the linkers to rotate. Rationalizing of the factors responsible for stabilization of mono- and di-protonated forms of the porphyrin core allowed us to suggest dendrimers with porphyrin cores as sensitive proton sensors with luminescent response for large pH ranges.
We also realized the importance of the direct conjugated linkage of the dendrons to the core for the further enhancement of the sensing ability of dendrimers with a porphyrin core. This is definitely the direction to explore in future research.
We found and studied complex formation between the dendrimers and some specific molecules including heterocycles and molecules containing nitrogen atoms and between porphyrin-based dendrimers themselves, which is important for the fundamental and applied research since it provides a basis for utilizing such compounds as molecular sensors and candidates for drug delivery.
The results of the project have both fundamental and applied importance.
During its implementation, scientists and students from Russia, Belarus, Germany, Belgium and Sweden accomplished more than 70 visits of the partners’ laboratories. The work has been presented on 17 international conferences and workshops, 21 peer-reviewed articles have been published by the end of the 3-year period. As the result this joint activity strong connections between Universities of Lund (Sweden), Leuven (Belgium), Technical University of Ilmenau (Germany) and Institute of Solution Chemistry (Russia) and B.I. Stepanov Institute of Physics (Belarus) have been developed at the scientific and educational levels. Importantly, the collaboration between the partners will continue in the future through long-term agreements on exchange and collaboration.
The project has a special socio-economical importance for the Institute of Solution Chemistry (Ivanovo, Russia) in the light of the current re-organization of the Russian Academy of Sciences.