Development of red-shifted Fei-Mao dyes with elongated polymethine chain and their imaging studies in plants

Abstract Fei-Mao (FM) dyes, amphiphilic styryl pyridiniums, are widely used as yellow or red fluorescent probes for visualizing the dynamic behavior of membrane compartments. In the present study, we developed red-shifted FM dyes functioning as near-infrared fluorescence probes. The newly developed FM dyes, which have 4 or 5 double bonds in their polymethine chain, exhibited emission maxima in the near-infrared region (≥681 nm) in plant cell membranes. Despite their low fluorescence quantum yields (≤1.5%), the red-shifted FM dyes exhibited sufficient fluorescence emission for microscopic imaging and could be used to visualize the dynamics of endocytic pathways. This study illustrates the potential and limitations of the polymethine elongation strategy for developing red-shifted FM dyes.