Daisuke Sawada

We describe a π‐topological transformation‐based synthetic method for the preparation of a new type of near‐infrared (NIR)‐emissive rhodamine dye called Polymethine‐embedded Rhodamine Fluorophore ( PeR Fluor ). In contrast to conventional NIR‐emissive dyes that require tedious synthetic steps and/or a high cost, linear fully π‐conjugated PeR Fluor can be regioselectively prepared in one step by mixing different nucleophiles with ABPXs, a family of rhodamines with a cross‐conjugated structure. PeR Fluor exhibits bright NIR fluorescence emission and high photostability owing to the cooperative π‐electron system of rhodamines and polymethine scaffolds. Large bathochromic shifts of the absorption and fluorescence emission maxima can be achieved by modifying the N ‐substituted group to obtain NIR‐absorbing/emitting PeR Fluor . We also demonstrate the stimulus‐responsive functionality of PeR Fluor through the addition of chemicals (acid/base), which shows switchable NIR and visible fluorescence response. Our π‐topological transformation‐based synthetic method is a promising approach to produce new functionalized rhodamine dyes.