Computational Analysis and Synthetic Strategies towards Novel Heavy-Chalcogenorhodamine Analogues for use in Dye-Sensitized Solar Cells, Dye-Sensitized Photocatalysts and the Inhibition of P-Glycoprotein
Calitree, Brandon David
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Detailed herein is the synthetic approach to prepare novel rhodamine analogues with 9-(3- or 4-carboxyphenyl) and 9-(3-nitrophenyl) substituents. Rhodamines analogues were prepared from xanthone precursors in a 'one-pot' procedure via Pd-mediated Suzuki cross coupling between a xanthone triflate and an arylboroxin. The procedure also works well with thio- and selenoxanthones. Rhodamine analogues with 9-(2-, 3- or 4-carboxyphenyl) substituents were evaluated as photosensitizers in dye-sensitized solar cells (DSSC) and dye-sensitized photocatalysts (DSP). Analogues with the 9-(2-carboxyphenyl) substituent containing O, S, and Se in the xanthene core showed the highest power conversion efficiencies (η%) of 0.23, 0.57 and 0.43, respectively, in DSSC; as well as giving turnover numbers (TON) as high as 9000 for the generation of hydrogen in DSP via the reduction of water using a cobalt(II) catalyst. Thiorhodamine derivatives containing amide and thioamide functionality have also been examined for their ability to stimulate P-glycoprotein (P-gp)-His 10 , to promote uptake of calcein AM and vinblastine into multidrug-resistant, P-gp-overexpressing MDCKII-MDR1 cells. Thioamide-derivatives were transported less rapidly then amide-containing derivatives. Time Dependent Density Functional Theory (TDDFT) and Natural Bond Order (NBO) analyses were used to evaluate a series of heavy chalcogen tetramethylrosamine dyes which have shown experimental trends of lowered excitation energies with increased chalcogen size. The computations indicated that the trend is a direct result of the heteroatom lone pair orbitals and the ability to contribute to the overall π-system.