Water-soluble 1,4-bis(4-aminostyryl)benzene derivatives for biological two-photon applications

1,4-Bis(4-aminostyryl)benzene derivatives have been shown to exhibit large two-photon cross-sections at ca. 730-745 nm and are typically highly fluorescent in organic solvents. For biological imaging applications, we have been interested in identifying water-soluble dyes with high two-photon cross-sections and fluorescence quantum yields. Four new bis(aminostyryl)benzene chromophores have been synthesized; these chromophores are functionalized with phosphate, sulfonate, and sulfate hydrophilic groups. In some cases, this substitution pattern renders the chromophores water-soluble and, for the sulfonate and sulfate cases, moderate fluorescence quantum yields are retained in water.