Correlation of Molecular Mechanics to the Red Shift in the Optical Absorption of Phenyl Substituted Porphyrins

Correlation of Molecular Mechanics to the Red Shift in the Optical Absorption of Phenyl Substituted Porphyrins

According to the results in experimental data, there was reason to believe that the red shift in the soret through protonation correlated with conformational changes as substituents were added on to the phenyl groups of the meso-tetra-phenyl porphyrin (TPP). The shift in wavelengths for the added substituents of carboxyphenyl and trimethylanillium on the T PP had minor changes on wavelength(s) shift. However, when analyzing the meso-tetra (p-hydroxyphenyl) porphyrin there seemed to be a strong correlation as to there not only being conformational changes in the porphyrin, but also high electronic contributions. This was observed by greater shifts of the Soret and by recognizing that the hydroxyl group takes part in strongly activating the porphyrin core donating its electrons. In the meso-tetra (m-hydroxyphenyl) porphyrin the electronic effect was still a contributing factor, but conformational changes were dominating because of steric interactions between the hydroxyl group and the porphyrin core. According to the MM+ model, the conformational changes were viewed as the more accurate contribution towards the meso-tetra (m-hydroxyphenyl) porphyrin. However, when the substituent groups in the para positions of the phenyl group are not strongly activating or deactivating groups, then there was no doubt to assume that the conformational changes in the para phenyl substituted porphyrins are strictly adhered to the porphyrin protonation.