Tellurapyrylium dyes

The Te(IIH>Te(IV) oxidation reactions of tellurapyrylium dyes 126 are much faster than reactions of the carbon 8-backbone. Singlet oxygen reacts with 126 (Y = Se, Te) with a second-order rate of about 10 dm3mol s l. An extremely high rate of oxidation was detected when ozone was used as an oxidant. The large second-order rate constant... 

The reaction serves as an illustrative example of the synthetic utilization of the Te(II)—>Te(IV) two-electron shuttle. Another promising application is seen in photodynamic therapy in which tellurapyrylium dyes 119 can function as photosensitizers to produce either singlet oxygen or superoxide radical-anions (via electron transfer), thereby serving as cytotoxic agents. An important useful property of tellurapyrylium dyes is their absorbance in the near-infrared region where biological tissues are most important. 

The tellurophenopyridazine (M) decomposed under the influence of light and oxygen to 4,5-dibenz-oylpyridazine (66) via the peroxide (65) derived from Diels-Alder reaction of singlet oxygen widi (64 Scheme 24). Tellurapyrylium dyes such as (67) react with singlet oxygen within a few seconds to give dihydroxides (68 Scheme 25). ... 

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