Adsorption orientation control of porphyrin on titania-nanosheet
2020
Tominaga, Shota | Sano, Keito | Hirade, Yugo | Shimada, Tetsuya | Ishida, Tamao | Takagi, Shinsuke
In this study, cis-di(N-methyl-2-pyridine)-diphenyl porphyrin (cis-DMPyP²⁺⁾was adsorbed on titania-nanosheet (TNS, Ti₀.₈₉□₀.₁₁O₂.₀₀⁰.¹¹⁻ (□: vacant)) monolayer film prepared by Langmuir-Blodgett method. The adsorption behavior such as maximum adsorption density and adsorption orientation change behavior of cis-DMPyP²⁺ were examined by absorption and dichroic waveguide spectroscopy, respectively. By the adsorption on TNS, the maximum absorption wavelength (λₘₐₓ) of cis-DMPyP²⁺ shifted from 421 to 456 nm in water. The maximum adsorption amount without aggregation was ca. 100% vs. cation exchange capacity of TNS. The orientation angle of cis-DMPyP²⁺ on TNS in water was less than 5°, that is porphyrin plane was almost parallel to the TNS surface. On the other hand, λₘₐₓ of cis-DMPyP²⁺ on TNS was 429 nm in ethanol. The adsorption orientation angle of cis-DMPyP²⁺ on TNS in ethanol was turned out to be 45°. These results indicate that the adsorption orientation angle of cis-DMPyP²⁺ depends on the solvent. It was demonstrated that the adsorption angle of organic molecules can be controlled on TNS surface by changing the solvent environments.
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