Productive Manipulation of Cyanine Dye π-Networks

Abstract

Polymethine bridges in cyanine dyes may be constrained by setting them into edge-fused ring systems, or extended by conjugation with carefully chosen heterocycles. Recent studies have shown that modifications like these can give significantly brighter dyes with red-shifted absorbance and emission maxima.

Keywords: cyanine; dyes; fluorescence; heptamethine.

Figure 1.

Schnermann’s route to conformationally constrained cyanines.

Figure 2.

Delocalizations around strategically placed heteroatoms increase the extent of significant resonance.

Figure 3.

Isomerization of the substituted cyanine 5c transforms it into a substituted merocyanine and significantly changes its fluorescence properties.

Figure 4.

The phenyl group of merocyanine 6 forces it to adopt an S-cis conformation wherein it shows a significant fluorescence enhancement on binding to a protein, which was attributed to the protein restricting rotation of the phenyl group.