6 research outputs found
Organotellurium Fluorescence Probes for Redox Reactions: 9‑Aryl-3,6-diaminotelluroxanthylium Dyes and Their Telluroxides
Several 9-aryl-3,6-diaminotelluroxanthylium
dyes with
phenyl, 2-methylphenyl, and 2,4,6-trimethylphenyl substituents at
the 9-position were prepared. The characterization of these compounds
included determination of <sup>125</sup>Te NMR spectra, fluorescence
quantum yields (Φ<sub>F</sub>), and quantum yields for the generation
of singlet oxygen [Φ(<sup>1</sup>O<sub>2</sub>)]. While these
compounds were essentially nonfluorescent (Φ<sub>F</sub> <
0.005), they produce <sup>1</sup>O<sub>2</sub> with Φ(<sup>1</sup>O<sub>2</sub>) between 0.43 and 0.90. The tellurorosamines were oxidized
with <sup>1</sup>O<sub>2</sub> via self-photosensitization to the
corresponding telluroxides, which allowed their preparation free of
excess oxidant. Telluroxides with a 9-(2-methylphenyl) or 9-(2,4,6-trimethylphenyl)
substituent were fluorescent with quantum yields for fluorescence
between 0.20 and 0.31. Steric bulk at the 9-position of the resulting
telluroxides impacted rates of inter- and intramolecular attack of
nucleophiles and stability of the telluroxide in aqueous media near
physiological pH. The yield of reduction of the telluroxide with glutathione
was also dependent on the steric bulk of the 9-aryl substituent. The
structure of products from oxidation of the 9-(4-bromophenyl) tellurorosamine
was determined by X-ray crystallography and indicated the addition
of oxygen nucleophiles to the 9-position of the telluroxide oxidation
state of the tellurorosamine
Synthesis and Properties of Heavy Chalcogen Analogues of the Texas Reds and Related Rhodamines
Analogues
of Texas red incorporating the heavy chalcogens S, Se,
and Te atoms in the xanthylium core were prepared from the addition
of aryl Grignard reagents to appropriate chalcogenoxanthone precursors.
The xanthones were prepared via directed metalation of amide precursors,
addition of dichalcogenide electrophiles, and electrophilic cyclization
of the resulting chalcogenides with phosphorus oxychloride and triethylamine.
The Texas red analogues incorporate two fused julolidine rings containing
the rhodamine nitrogen atoms. Analogues containing two “half-julolidine”
groups (a trimethyltetrahydroquinoline) and one julolidine and one
“half-julolidine” were also prepared. The photophysics
of the Texas red analogues were examined. The S-analogues were highly
fluorescent, the Se-analogues generated single oxygen (<sup>1</sup>O<sub>2</sub>) efficiently upon irradiation, and the Te-analogues
were easily oxidized to rhodamines with the telluroxide oxidation
state. The tellurorhodamine telluroxides absorb at wavelengths ≥690
nm and emit with fluorescence maxima >720 nm. A mesityl-substituted
tellurorhodamine derivative localized in the mitochondria of Colo-26
cells (a murine colon carcinoma cell line) and was oxidized <i>in vitro</i> to the fluorescent telluroxide