Squaraines are a class of organic dyes with unique absorption and fluorescence properties. Due to their donor-acceptor-donor structure, they typically have a sharp and intense absorption in the red to NIR region. In the field of organic solar cells, qualitative good substances that absorb light in the NIR region are still missing. Low band gap polymers and small molecule dyes are potentially suitable materials for organic solar cells due to the intrinsic conductivity and light harvesting properties respectively. In our group, dye polymers are synthesized to investigate the combination of the aforementioned.

The properties of squaraines can be tuned by exchange of the central acceptor unit, by variation of the outer donor units or by addition of further chromophores. In our group, all those variation possibilities are used to design various monomeric squaraine dyes as model compounds for potential low band gap polymers which are than synthesized via polycondensation reactions. The syntheses include basic standard reactions like condensations, alkylations or Fischer-Indole-Synthesis. Furthermore, various transition metal assisted or catalyzed reactions like for example the Yamamoto-, Buchwald-Hartwig- or Suzuki-coupling are applied.

Investigation of the spectral and electronic properties by absorption- and fluorescence measurements, cyclovoltammetry and spectroelectrochemistry enables the comparison of monomeric and polymeric substances like red shift and broadening of the absorption due to exciton coupling for example. Suitable substances are than further investigated as materials in organic solar cells by our cooperation partners.