Abstract
We have used a combination of computational methods with spectroscopic analyses to investigate the effect of substituents on the β-pyrrolic position of porphyrin systems.
Certain types of substituents perturb the frontier molecular orbitals of the porphyrin to significantly change the electronic absorption spectrum through the introduction of new non-porphyrin transitions. There new transitions have been characterised by resonance Raman spectroscopy and are predicted by density functional theory. They offer a further method of altering the electronic spectral properties of porphyrin systems. We have studied a very wide range of these groups from thiophene systems through indandione substituents.
For example, in a study of porphyrins with indandione substituents we found that the electronic absorption spectrum showed significant perturbation with a long wavelength feature at 681 nm being attributed to the indandione moiety as evidenced by enhancement of modes associated with this group in the resonance Raman spectrum.