Self-Deprotonation and Colorization of 1,3-Bis(dicyanomethylidene)indan in Polar Media: A Facile Route to a Minimal Polymethine Dye for NIR Fluorescence Imaging

Colorless 1,3-bis(dicyanomethylidene)indan is an organic acid (pKa approximate to 3.0) that turns blue in polar media owing to self-deprotonation. Moreover, its colored conjugate base shows potential as a minimal anionic polymethine dye for probing biomolecules in cells and in vivo through noncovalent complexation and near-infrared fluorescence signaling.