Resonance Raman Enhancement of the ν4 Band in Fe (TMPP)Cl at NIR Laser Excitation Attributed to Supramolecular Interaction

Abstract

The strong enhancement when applying near-infrared excitation wavelengths, of totally symmetric modes of heme derivatives including β-hematin (malaria pigment), was hypothesized to be due to supramolecular interaction. Specifically, the intensity of the electron density or oxidation state marker band, ν4, is in part strongly affected by CH(((X hydrogen bonding interactions when X is an electron-donating entity. Chlorotetra (p-methoxyphenyl) porphyrinatoiron (III), Fe (TMPP)Cl, is a model compound that supports this hypothesis. The single crystal X-ray structure of Fe (TMPP)Cl, recrystallized by vapor diffusion of diethyl ether into dichloromethane solution, was determined. There are πpor···πpor interactions and numerous additional supramolecular interactions in the form of CH···Cl and CH···O, and CH···π hydrogen bond interactions. The corresponding resonance Raman intensity of Fe (TMPP)Cl exhibited great enhancement of the ν4 band when using 780 and 830 nm laser sources supporting the correlation of the strong CH(((X hydrogen bonding interaction and the strong resonance Raman enhancement of totally symmetric modes, especially ν4, observed in malaria pigment supramolecular arrays when applying near-infrared wavelengths.