Facile synthesis of monofunctional pentamethine carbocyanine fluorophores

A high-yield route to symmetric, conjugatable pentamethine carbocyanine dyes with far-red/near infrared (NIR) emission between 650 and 700 nm is reported. The dyes are prepared via condensation of indolium or benz[e]indolium inner salts with an alkyl carboxylic acid derivatized malonaldehyde dianil or alternatively in a one-pot reaction without isolation of the malonaldehyde intermediate. The fluorophores are water-soluble, have bright fluorescence emission, are easily prepared in good yield, and are promising candidates for use in a variety of biochemical and in vivo imaging applications.

Research highlights
► Water-soluble, near-infrared conjugatable symmetric carbocyanine fluorophores.
► High-yielding one-pot synthetic procedure.
► Strong fluorescence emission with improved photostability.