Dependence of the Molecular Adsorption Orientation and Photo-Absorption Behavior of Porphyrins on the Surface Property of Inorganic Nanosheets.

Organic/inorganic hybrids have been extensively studied across various research fields. However, the presence of kinks, steps, and terraces and the exposure of different crystal faces on inorganic surfaces complicate the understanding of molecular adsorption behavior. Nanosheets, plate-like particles with nanometer-scale thickness, provide uniform adsorption sites due to their atomically flat surfaces and high crystallinity. This study investigates the adsorption behavior of cationic porphyrin (-DMPyP) on anionic niobia, titania, and clay nanosheets (NNS, TNS, and CNS, respectively). Absorption and fluorescence spectroscopies revealed that -DMPyP densely adsorbed on the NNS surface in a monomeric phase with up to 75% surface coverage. The adsorption orientation angle relative to the nanosheet surface () was 41°, whereas a parallel adsorption state ( ∼ 0°) was previously observed on the TNS and CNS surfaces. This difference arises from the weaker hydrophobic interactions between -DMPyP and NNS, as NNS has a more hydrophilic surface compared to TNS and CNS. In pyridinium-based porphyrins, the excitation energy shift increases as decreases due to the surface-fixation effect on the nanosheet surface. Since depends on the surrounding medium, this research will aid in extrinsically controlling the adsorption and absorption properties of organic/inorganic hybrids to enhance their intriguing characteristics fully.