Fig.9 Some squaramide-linked glycoconjugates with special functions [158-161]

ho2ch2c \_/ ch2co2h

In the squaraine chemistry, biologically interesting heterocyclic squaryl-ium dyes are also being explored (Fig. 11). Potential usefulness in photo-dynamic therapy was envisioned by effective singlet oxygen generation of benzothia(selena)zole-derived squarylium dye 207 and halogenated squaryl-ium dye [175,176]. Some chemosensors for some metal ions were based on the red-fluorophore of azacrown-appended squarylium dyes 208. Related podand-based (H-aggregation) squarylium dyes 209 were demonstrated to detect alkaline and earth-alkaline metal ions (Na+, K+, Mg2+, Ca2+) selectively [177,178]. Carbohydrates and proteins were monitored by labeling with properly functionalized symmetric and asymmetric dyes (e.g., 210) [179182].

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