Ultrabright and Serum-Stable Squaraine Dyes
Yogesh Yadav, Eric A. Owens, Shinsuke Nomura, Takeshi Fukuda, Yoonji Baek, Satoshi Kashiwagi, Hak Soo Choi, Maged Henary
Abstract
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.