Syntheses and spectroscopic properties of energy transfer systems based on squaraines

The purpose of this project was to prepare fluorescent dyes that could absorb energy at relatively short wavelengths, and fluoresce in the near-IR region. To achieve this, copper- and palladium-mediated C–N couplings were used to prepare the ‘cassettes’, i.e the carbazole derivative and the carbazole-, phenothiazine-, and phenoazine-squaraines . These compounds have carbazole, phenothiazine, and phenoazine donor-components that absorb around about 300–320 nm, and squaraine acceptor-parts that fluoresce in the range 650–700 nm. The efficiencies of energy transfer from the donor to the acceptor, and the overall quantum yields of the cassettes were determined.