"Design, Synthesis, and Photophysical Properties of Novel Chalcogenorhodamine Dyes for Various Applications"
Kryman, Mark William
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Chalcogenorhodamine dyes bearing thioamide or amide moieties are transported at different rates by P-gp, with amide-containing dyes being transported more rapidly than the analogous thioamide derivatives. Additionally, thiorhodamine dyes with fused ring moieties at the 3-amino position have shown decreased ATPase stimulation and increased binding affinity for P-gp relative to the analogous dimethylamino dyes. Based on these results, a synthetic route toward a new rhodamine precursor with fused ring moieties at both 3- and 6- amino positions, the bis(julolidyl) xanthone (57-E), was developed. The two julolidyl moieties impart added rigidity, increased lipophilicity, and bathochromic shifts in the wavelength of maximum absorption in the resulting dyes. The thioamide- and amide-containing bis(julolidyl) selenorhodamines are more effective photosensitizers in the PDT of P-gp-expressing cancer cells, with EC 50 values an order of magnitude lower than previously reported selenium-containing photosensitizers. The bis(julolidyl) selenorhodamine 6 is rapidly transported by P-gp, localizes in the mitochondria of cancer cells, and selectively photodepletes malignant T cells while sparing T cells necessary for healthy immune function. Several tellurorhodamines with phenyl, 2-methylphenyl, and 2,4,6-trimethylphenyl substituents at the 9-position were prepared and evaluated for their potential use as reversible fluorescence probes based on a Te(II)/Te(IV) redox cycle. While the tellurides were essentially nonfluorescent (f FL < 0.005), they were found to produce 1 O 2 with f( 1 O 2 ) between 0.43 and 0.90. The tellurides were oxidized with 1 O 2 via self-photosensitization to the corresponding telluroxides. Telluroxides with a 9-(2-methylphenyl) or 9-(2,4,6-trimethylphenyl) substituent were fluorescent with f FL 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 the subsequent stability of the telluroxide in aqueous media near physiological pH. The reversibility of the Te(II)/Te(IV) fluorescence probe was also dependent on the steric bulk of the 9-aryl substituent. Telluroxides functionalized with a 9-(2,4,6-trimethylphenyl) substituent displayed increased hydrolytic stability and reversibility relative to those bearing a 9-phenyl or 9-(2-methylphenyl) substituent. Bis(julolidyl) and bis(half-julolidyl) rhodamine analogues with phosphonic, carboxylic, and hydroxamic acid anchoring groups were synthesized and evaluated as photosensitizers in dye-sensitized solar cells (DSSCs) and dye-sensitized photocatalysts (DSPs). Phosphonic acid and hydroxamic acid functionalized dyes maintained similar incident photon to current conversion efficiencies (IPCEs of 52-64%) over a 100 min time period while the IPCE values of the analogous carboxylic acid derivatives decreased rapidly. Desorption studies in acidified acetonitrile show that the phosphonic acid derivatives bind more tightly to TiO 2 relative to the analogous carboxylic and hydroxamic acids over a 48 h time period. Additionally, preliminary results show that the phosphonic acid 36 generates 3500 turnover numbers (TONs) of hydrogen within 48 hours, 3-4 times more than the analogous carboxylic and hydroxamic acid derivatives. These results suggest that the phosphonic acid may be a more efficient anchoring group for DSSC and DSP systems. Lastly, a new class of NIR absorbing extended rhodamines with extended conjugation in the xanthylium core has been designed and synthesized. The synthesis of both 'linear' and 'bent' extended rhodamines was accomplished through the selective directed ortho -metallation (D o M) of a 2-naphthamide. The resulting 9-phenyl dyes exhibit extension of absorption maxima into the near-IR, high molar extinction coefficients, broadened absorption bands, and large Stokes shifts. These dyes are attractive leads for biological and solar energy conversion applications.