The adsorption of large biomolecules such as proteins is of high relevance in medicine; adsorbed proteins can initiate undesirable biological reactions such as blood coagulation or immune responses, which adversely affect the human body and the functioning of medical devices. Thus, the suppression of protein adsorption onto material surfaces is essential for medical and biomedical applications. Interfacial water molecules may play a key role in protein adsorption. In this context, in this study, we prepare various types of surfaces (hydrophobic, hydrophilic, anionic, cationic, and zwitterionic) using polymer brushes with different molecular structures. We analyze the adsorption of negatively and positively charged proteins using a quartz crystal microbalance (QCM) to quantitatively investigate protein adsorption onto the polymer brush surfaces. The structure of the interface between the polymer brushes and water media is investigated using sum frequency generation (SFG) spectroscopy. Our comparison of the protein adsorption characteristics with the properties of the interfacial water molecules of each polymer brush indicates that the interfacial water molecules, which strongly interact with polymer brushes, are important for suppressing protein adsorption. The findings can significantly contribute to the functional biomaterial design.

Disulfides, with a series of alkyl spacers containing porphyrins at both ends, were prepared to evaluate the effect of the spacer length on the interfacial structure and photoelectrochemical properties of selfassembled monolayers (SAMs) on a gold electrode. The structure of the SAMs was investigated using UV-visible absorption spectroscopy, cyclic voltammetry, and photoelectrochemical studies. These measurements showed that as the length of the spacers increases, the SAMs tend to form a highly ordered structure on the gold electrode. Photoelectrochemical studies, using modified Au and Pt electrodes, were carried out in the presence of methyl viologen as an electron carrier. The photocurrents decrease dramatically with a decrease in the spacer length, indicating that there are two competitive deactivation pathways for the excited porphyrin, i.e., the quenching by the electrode and electron carrier.

Three different kinds of C 60 alkanethiols have been prepared by changing systematically the linking positions, ortho, meta, and para, at a phenyl group on a pyrolidine ring fused to the C 60 moiety. Electrochemical measurements showed that well-ordered structures are formed in self-assembled monolayers of these C 60 alkanethiols on gold electrodes. Photoelectrochemical studies were carried out using gold electrodes modified with self-assembled monolayers of the C 60 . A stable anodic photocurrent was observed in the presence of an electron sacrificer when the modified gold electrode was illuminated with a monochromic light. Dependence of the photocurrents on the applied potential together with the agreement of the action spectra with the absorption spectra support the following photocurrent generation mechanism: the generation of a vectorial electron flow from the electron sacrificer to the gold electrode via the excited triplet state of the C 60 . The quantum yields vary from 7.5% to 9.8%, depending on the linking positions.

Self-assembled monolayers (SAMs) technique has been applied to porphyrin-linked fullerene systems to mimic supramolecular photoinduced charge-separation (CS) events in photosynthesis. Porphyrin-linked C60 molecules with a sulfide group were designed to self-assemble on a gold surface using S–Au interaction. The structure of the SAMs formed on gold electrodes was investigated by spectroscopic methods including X-ray photoelectron spectroscopy (XPS), ultraviolet (UV)-visible spectroscopic ellipsometry, UV-visible absorption spectroscopy, and Fourier transform infrared (FTIR) spectroscopy as well as electrochemical studies. These results indicate that the SAMs have loosely packed structure; the porphyrin-C60 molecules are tilted and nearly parallel onto the gold surface. Short-circuit photocurrent with a level of sub-μA cm−2 was observed for the photoelectrochemical cell in the presence of methylviologen (MV) under illumination with ca. 4 mW cm−2. The maximum intensity of the photocurrent in free-base porphyrin-C60 system is five times larger than that in the corresponding free-base porphyrin system, indicating that C60 is an effective mediator in multistep electron transfer (ET) processes. A possible mechanism for the photocurrent generation is discussed in terms of the photodynamics of porphyrin-linked fullerenes in solution.