Ultrabright and Serum-Stable Squaraine Dyes

Highly stable symmetric and asymmetric
squaraine fluorophores have
been synthesized featuring an internal salt bridge between a quaternary
ammonium cation and the central oxycyclobutenolate ring of the chromophore.
Some of our newly synthesized symmetric and asymmetric compounds display
increased molar absorptivity, quantum yield in serum, and thermal/photochemical
stability over previously reported squaraine-based dyes. Consequently,
both classes show great promise in resurfacing the normal environment-labile
squaraine dyes as novel imaging agents and scaffolds for fluorescence
sensing. Furthermore, incorporating a covalent attachment point away
from the conjugated system allows for biological tagging applications
without disturbing the optimum optical characteristics of the newly
designed fluorophore.