Design of novel dyes towards the near-infrared
A series of seven functionalized near-infrared aza-BODIPY dyes have been synthesized and their spectroscopic properties measured. Their fluorescence emissions could be tuned by altering the electronic substituents on the aryl-groups. A through-bond energy transfer cassette featuring two fluorescein units as donor, and an aza-BODIPY dye as acceptor, was then synthesized and its preliminary spectroscopic properties examined. This cassette exhibited absorption and fluorescence characteristics that were highly dependent on the pH and the solvent polarity. Furthermore, no energy transfer was observed upon excitation of the donor. Novel near-infrared aza-BODIPY were also synthesized via a one-pot, two step reaction. Upon demethylation and intermolecular cyclization onto the B-atom, a ~ 100 nm red?shift of both the absorption and fluorescence emission maxima could be observed. Through-bond energy transfer cassettes based on squaraines have also been synthesized and their spectroscopic properties studied. These cassettes exhibited fast and efficient energy transfer from the donor to the acceptor. In depth experiments have also been realized to correlate the rate of energy transfer and structure on 3 different sets of through-bond energy transfer cassettes. No correlations could be made between the rate of the energy transfer and the nature of the acceptor, and the distance between the donor and acceptor. Finally, the use of DPP (diketo-pyrrolopyrolle) pigment as a potential donor for through-bond energy transfer cassettes was investigated. Three water-soluble DPPs dyes were prepared and studied. They all displayed weak fluorescence in water.