Push–pull fluorophores based on NHS esters of bithiophene for labelling of biomolecules containing primary amines

Fluorescent labelling is a versatile tool to visualize biomolecules containing primary amines in their cellular environment, allowing the study of their function or interactions. Here, three organic fluorophores that can irreversibly bind to the primary amine group on the target biomolecule are reported. They consist of push-pull heterocyclic dyes based on bithiophene and incorporating a terminal <i>N</i>-hydroxysuccinimidyl ester as a reactive group for labelling primary amine groups from biomolecules as (poly)amines, peptides or proteins. Their potential as chemosensors for primary amines, using N_α-Boc protected amino acid l-lysine as a model, was assessed through UV-Visible, fluorescence and ¹H NMR titrations.