Chiroptical Properties of Oligomeric Squaraine Dyes

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Chiral chromophores are widely used as chiroptical molecular sensors, as catalyst in photochemical reactions and as emitters in OLEDs with circular polarized luminescence (CPL). The generation of strong chiroptical effects, that is, a high rotatory strength of circular dichroism and an intense circular polarized luminescence, are in focus of the development and application of chiral chromophores. Molecular oligomeric and polymeric squaraine dyes also possess a broad potential for applications in biomedicine and optoelectronic devices. They show intense absorption bands in the red to near-infrared spectral region with high fluorescence quantum yields. Thus, we intend to use these advantageous optical properties and to extend them with chiroptical properties. The synthesis of chiral oligomeric squaraine dyes and the characterisation of their chiroptical properties for future applications in optoelectronic devices thus is the prime goal of this project. Hereby, we shall incorporate the chiral centre directly into the pi-system of the indolenine squaraine dyes, and not, as has be done in previously known chiral squaraines, by simply attaching chiral side chains. In that way, we hope to increase the chiroptical properties significantly. These properties shall further be enhanced by the synthesis of dimers and helical foldamers, because for oligomers we expect a coupling of optical transitions of monomeric squaraines by the exciton chirality effect.