Anellated Hemicyanine Dyes with Large Symmetrical Solvatochromism of Absorption and Fluorescence

A novel class of amphiphilic hemicyanine dyes is described where electron-pushing aniline and electron-pulling pyridinium are joined by anellated benzene rings. Enhancing the solvent polarity, the absorption band of these ANNINE dyes is shifted to the blue and the fluorescence band is shifted to the red at an invariant 00 energy. The increasing Stokes shift spans the whole visible spectrum. The divergent symmetrical solvatochromism of the positively charged chromophores is parametrized by a monopole−dipole model using a Born−Onsager−Marcus approach. From the intramolecular charge shift that is induced by electronic excitation, the linear Stark effect that is expected when the ANNINE dyes are used as voltage-sensitive probes in a biomembrane is estimated.