Highly ordered surface structure of large-scale porphyrin aggregates assembled from protonated TPP and water

• A doublet finding near 1000 cm−1 establishes proton sharing in water–porphyrin complex.
• The 1608 and 1483 cm−1 frequencies characterize behavior of protonated dimeric complex.
• Vibrational properties of water confined in aggregates depend on solid or liquid support.
• Highly ordered structures of the protonated TPP aggregates are found by SEM.
• Structural features on the surface indicate an intimate relation to liquid water structure.

Large-scale aggregates assembled from protonated meso-tetraphenylporphine (TPP) dimers and water have been investigated by IR and resonance Raman spectroscopy and also by scanning electron microscopy (SEM). It was found that the properties of water confined in the aggregates depend on the physical state of the support. When the aggregates were deposited on a solid CaF2 plate, they showed properties consistent with a quasi-crystalline structure. But when the aggregates were dispersed in oil, their IR characteristics were different; the vibration bands of the confined water were like those of water in liquid state. A doublet at about 1000 cm−1, components of which have been attributed to specific vibrations of H3O+ and H2O bound in the structure of water-porphyrin dimeric complex, was found in IR and resonance Raman spectra (λex = 441.6 nm) of protonated TPP aggregates. This doublet indicates the hydrogen ion involving in the vibrational system of water-porphyrin dimeric complex with hydrogen bonding by similar way as in so-called Zundel cation. The resonance Raman spectrum shows evidence for proton sharing between protonated water dimer and N groups of the pyrrole rings. SEM results indicate that the large-scale aggregates of the protonated porphyrin possess highly ordered structure, are only observed when using extremely pure water.