Protic Properties of Water Confined in the Pores of Oxidized Porous Silicon Studied by Excited-State Proton Transfer from a Photoacid

Abstract

The properties of water confined in the pores of oxidized porous silicon (PSi) were studied using the wellknown photoacidic 8-hydroxy-1,3,6-pyrenetrisulfonate trisodium salt. We used porous silicon samples, whose pores have an average diameter of 10 nm and a depth of 2 µm. We found that the rate of the excitedstate proton transfer to water in PSi pores is slightly enhanced with respect to bulk water. We found that the transferred proton reaches the pore's walls and is subsequently reflected back with no appreciable loss. Since the proton diffusion occurs inside the elongated space of the cylindrical pore the proton-photoacid molecule pair distribution function tends to deviate from spherical symmetry at long times. The detailed analysis of the time-resolved emission of the protonated species of the photoacid (ROH*) shows that at long-times after excitation the diffusion space is nearly two-dimensional, and consequently it does not have a spherical symmetry.

Photochemistry and Photophysics in Silica-Based Materials: Ultrafast and Single Molecule Spectroscopy Observation

“…Thus, the H-bonding interactions between HPTS and the MCM41 framework and the restricted diffusion space available to the adsorbed HPTS result in slower dynamics . However, a different behavior was observed when HPTS interacts with other SBMs such as alumino-silica surfaces and hydrated porous silicon (10 nm pore size). , For both complexes, the ESPT mechanism is similar to that observed for HPTS in bulk water. This similarity is because the HPTS molecules are covalently linked to the alumino-silica surfaces and retain their photoacid character, while in the hydrated porous silicon, the large pore size of the host does not affect the ESPT dynamics. , Clearly, the different behaviors of HPTS when interacting with these materials reflect how the molecular environment and the restriction of the host affect the ESPT reaction of the PT dye and its related dynamics.…”

“…However, a different behavior was observed when HPTS interacts with other SBMs such as alumino-silica surfaces and hydrated porous silicon (10 nm pore size). , For both complexes, the ESPT mechanism is similar to that observed for HPTS in bulk water. This similarity is because the HPTS molecules are covalently linked to the alumino-silica surfaces and retain their photoacid character, while in the hydrated porous silicon, the large pore size of the host does not affect the ESPT dynamics. , Clearly, the different behaviors of HPTS when interacting with these materials reflect how the molecular environment and the restriction of the host affect the ESPT reaction of the PT dye and its related dynamics.…”

“…This similarity is because the HPTS molecules are covalently linked to the alumino-silica surfaces and retain their photoacid character, while in the hydrated porous silicon, the large pore size of the host does not affect the ESPT dynamics. 188,192 Clearly, the different behaviors of HPTS when interacting with these materials reflect how the molecular environment and the restriction of the host affect the ESPT reaction of the PT dye and its related dynamics.…”

Study of Thioflavin-T Immobilized in Porous Silicon and the Effect of Different Organic Vapors on the Fluorescence Lifetime

“…Samples were prepared using p-type doped Si substrates, which were 405–645 μm thick with a resistivity of 0.01–0.02 Ω cm and (100) crystal orientation, obtained from WaferNet Inc. Details of the fabrication process can be found elsewhere . Briefly, electrochemical etching was performed using an electrolyte solution containing 15% HF solution, and the current was applied using a Princeton Applied Research 273A potentiostat.…”

“…Details of the fabrication process can be found elsewhere. 27 Briefly, electrochemical etching was performed using an electrolyte solution containing 15% HF solution, and the current was applied using a Princeton Applied Research 273A potentiostat. The surface exposed to the solution was 1 cm 2 .…”