Hierarchical Self-organization of Cyclic Chromophore Arrays for Artificial Light Harvesting
Zusammenfassung der Projektergebnisse
Multichromophore supramolecular cyclic arrays are common structural motifs of natural light harvesting systems. The structural beauty and intriguing functional properties of such natural dye arrays have inspired chemists to develop their artificial counterparts, and thus this has been an active research field in past decade. However, for the ration design of multichromophore cyclic dye assemblies with light harvesting function in-depth understanding of photophysical characteristics of individual dye constituents in cyclic assemblies is of crucial interests. Therefore, the aim of this project was the detailed characterization of photophysical properties of monomeric perylene bisimides (PBIs) by single-molecule spectroscopy, and then investigate the supramolecular cycles of these monomeric dye units to understand their mutual interactions in the assembly. Thus, we have studied the photophysical parameters of three PBI dyes by single-molecule spectroscopy, time-resolved spectroscopy, and fluorescence-correlation spectroscopy revealing high fluorescence lifetimes, low singlet to triplet intersystem crossing rates and short triplet lifetimes. These photophysical characteristics qualify the PBI dyes as excellent fluorophores for light harvesting cyclic arrays. We have then studied the single molecule photophysical properties of a dimer system consists of two identical PBI units that are covalently linked through a calix[4]arene spacer. These studies revealed photoinduced radical anion formation of one of the PBI units in this dimer and different energy transfer rate from the neutral PBI molecule to the radical anion species, leading to various photoblinking behaviours. According to our original project plan, we have also attempted singlemolecule spectroscopic investigation of a metallosupramolecular PBI cycle but unfortunately failed due to the insufficient thermodynamic stability of the metallosupramolecular bonds upon dilution. Despite we have explored the self-organization behaviour of this PBI cyclic array on HOPG surface by AFM and found that it forms honeycomb-structured two-dimensional nanopatterns possessing some resemblance to the supramolecular organization of dyes in photosynthetic membranes. Although some of the envisioned goals of this project could not be achieved yet, our results are encouraging for further investigations of PBI cycles by different modern spectroscopic techniques, including single-molecule spectroscopy; however, for the latter design and synthesis of appropriate cyclic scaffolds need to be approached in future. In this regard we recently accomplished the synthesis of the first covalently connected PBI macrocycles which are studied in the framework of the DFG-funded research group 1809 “Light-induced dynamics in molecular aggregates” at the University of Würzburg.
Projektbezogene Publikationen (Auswahl)
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Comparison of the Photophysical Parameters for Three Perylene-Bisimide Derivatives by Single-Molecule Spectroscopy Chem. Phys. Chem. 2007, 8, 1487-1496
E. Lang, R. Hildner, H. Engelke, P. Osswald, F. Würthner, J. Köhler
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Hierarchical Self-Assembly of Cyclic Dye arays into Two-Dimensional Honeycomb Nanonetworks Small 2008, 4, 2158-2161
V. Stepanenko, F. Würthner
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Photoblinking Dynamics in Single Calix[4]arene-linked Perylene Bisimide Dimers Chem. Phys. Lett. 2009, 482, 93-98
D. Ernst, R. Hildner, C. Hippius, F. Würthner, J. Köhler
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Self-assembly and layer-by-layer deposition of metallosupramolecular perylene bisimide polymers J. Mater. Chem. 2009, 19, 6816–6826
V. Stepanenko, M. Stocker, P. Müller, M. Büchner, F. Würthner
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Single molecule studies of calix[4]arene-linked perylene bisimide dimers: Relationship between blinking, lifetime and/or spectral fluctuations Phys. Chem. Chem. Phys. 2012, 14, 10789-10798
A. Issac, R. Hildner, D. Ernst, C. Hippius, F. Würthner, J. Köhler
