Molecular push-pull nanographene-derivatives as vis/NIR fluorescent dyes

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The aim of this research project is to prepare and characterize new fluorescent dyes based on the diaminodicyanoquinone (DADQ) motif in order to derive structure-property relationships for the optical spectroscopic and photophysical properties of these DADQ derivatives in different microenvironments and nanostructures. This implies the following steps: First, nanographene-like push-pull dyes with DADQ motif are synthesized. Here, imidazole donor and dicyanomethylene acceptors are incorporated as push- and pull- substituents, respectively. The pi-systems are extended based on the hexabenzocoronene (HBC) motif and the pentaphene motif, which we discovered recently. The aim is to here to shift the absorption and emission bands of these DADQ derivatives to longer wavelength relative to the basic DADQ motif. Then, functionalization with polar and ionic groups is performed at the periphery of the chromophoric motif to control the local polarity and aggregation behavior. In addition, the solubility is varied by substituents such as alkyl, F-containing alkyl or ether groups. Subsequently, the optical and photophysical properties of the prepared DADQ derivatives are studied in microenvironments of different polarity and/or proticity and viscosity to identify DADQ structures with particularly interesting fluorescence properties (moderate to high quantum yields; preferably long-wavelength fluorescence) and high photostability. For this purpose, steady state and time-resolved fluorescence studies are performed in different solvents and solvent mixtures to determine the molecular environments/environmental parameters relevant for efficient fluorescence, such as polarity and viscosity. For selected DADQs, the temperature dependence of fluorescence is also investigated for mechanistic conclusions. Furthermore, the optical spectroscopic properties of the prepared DADQ derivatives in the solid state or crystal are investigated as well as the aggregation behavior of selected DADQs in different microenvironments and their photostability. Based on these results, interesting DADQ dyes are selected for the incorporation into water-dispersible nanostructures of different material compositions and thus varied polarity such as polymer and silica particles (non-porous; mesoporous) of different sizes. In addition, the encapsulation of DADQ dyes in micellar structures is investigated. By comparing the optical and photophysical properties of the DADQ derivatives in particles or micellar systems with those in solution and in the solid state, structure-property relationships can be derived, especially for the DADQ fluorescence as well as their potential for future use as a novel dye class.