Thio-squaraines

The photostability of ring-substituted squaraines, especially dicyanomethylene-and f/no-squaraines is, in general, higher compared to oxo-squaraines and cyanines (Fig. 2). Increasing of the number of sulfo groups further improves the photostability of these dyes the photostability for hydrophilic dyes increases in the order 10b < 13b < Cy5 < 41h < 41i 41j < 41f < 41g [18]. Thio-squaraine dyes... 

Due to their displayed higher photostability, indolenine-based cyanines and squaraines are preferred for the design of fluorescent tracers. Dicyanomethylene- and thio-squaraines with substituted squaraine oxygens also show potential as highly photostable fluorescent probes. 

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