Organotellurium Fluorescence Probes for Redox Reactions: 9-Aryl-3,6-diaminotelluroxanthylium Dyes and Their Telluroxides

Abstract

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 125Te NMR spectra, fluorescence quantum yields (ΦF), and quantum yields for the generation of singlet oxygen [Φ(1O2)]. While these compounds were essentially nonfluorescent (ΦF < 0.005), they produce 1O2 with Φ(1O2) between 0.43 and 0.90. The tellurorosamines were oxidized with 1O2 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

“…20 To this end, 9-mesityltellurorhodamine 27 was prepared in 83% yield by the addition of the Grignard reagent from 2-bromomesitylene to telluroxanthone 2-Te at ambient temperature in THF followed by work-up with aqueous HPF 6 (Scheme 5). Tellurorhodamine 27 absorbed light with a λ max of 617 nm and ε of 1.65 × 10 5 M –1 cm –1 in MeOH (Table 2).…”

Core–shell polymeric nanoparticles co-loaded with photosensitizer and organic dye for photodynamic therapy guided by fluorescence imaging in near and short-wave infrared spectral regions

“…Singlet oxygen generation was also evaluated directly via its luminescence (phosphorescence) emission peaked at 1270 nm [28,29]. A Fluorolog-3 spectrofluorometer equipped with an infrared spectrometer (iHR320, Horiba) was employed to detect singlet oxygen emission.…”

Moving Beyond Boron-Based Substituents To Achieve Phosphorescence in Tellurophenes

“…[25][26][27] A number of structurally novel luminescent (predominantly fluorescent) tellurium complexes have also been synthesized recently. [28][29][30][31][32][33][34][35][36][37] Particularly salient examples include the tellurium-containing dibenzobarrelenes prepared by Ishii and coworkers, 33 and fluorescent xanthyliumbased tellurones reported by Detty and coworkers. 31 Thus far, published tellurophene emitters from our laboratories each share a common structural motif: namely, the presence of proximal BPin substituents at the 2-and/or 5-positions of a tellurophene (or benzotellurophene) ring.…”

“…[28][29][30][31][32][33][34][35][36][37] Particularly salient examples include the tellurium-containing dibenzobarrelenes prepared by Ishii and coworkers, 33 and fluorescent xanthyliumbased tellurones reported by Detty and coworkers. 31 Thus far, published tellurophene emitters from our laboratories each share a common structural motif: namely, the presence of proximal BPin substituents at the 2-and/or 5-positions of a tellurophene (or benzotellurophene) ring. 24,38 In addition, these compounds have been shown to be non-emissive in aerated solutions, leaving two possible dominant quenching pathways: 1) non-radiative quenching of excited triplet states (Tn) mediated by O2, and/or 2) non-emissive relaxation modulated through molecular vibration/rotation or solvent interactions.…”