Magnetic Circular Dichroism Studies. 62.¹Sign Variation in the Magnetic Circular Dichroism Spectra of Some Perimeter Symmetric Free-Base Porphyrins

Magnetic circular dichroism spectroscopy of cobalt tetraphenyltetraacenaphthoporphyrin

“…Our earlier analysis of a reversal in the alignment of the l À moment due to the differing effects of ligand folding on the orbital angular momentum (OAM) properties of the HOMOs and the LUMO can be applied here as well. As has been observed previously by Djerassi and coworkers [26][27][28], structural perturbations, which result in a significant DHOMO value, tend to initially reverse only the sign of the A 1 term associated with the Q band. When jDHOMO À DLUMOj is small, the introduction of the larger l + moment into Eqs.…”

Electron-Withdrawing meso-Substituents Turn On Magneto-Optical Activity in Porphyrins

“…Djerassi has argued that the a 2u orbital is actually lower in energy than the a 1u orbital in Zn(TPFPP), whereas this ordering is reversed in Zn-(TPP). 44,48 However, recent calculations on Pd(TPFPP) show the a 2u to be of higher energy than the a 1u orbital. 49 Nevertheless, the precise ordering of these orbitals and their energy difference will be determined by a complicated mix of interactions involving the meso-substituent, metal based orbitals and the a 2u orbital.…”

“…In this series of complexes, the a 1u orbital is essentially constant as only the a 2u orbital features atomic contributions from the meso -carbon atoms (the electronics of which are perturbed by attachment to either C 6 H 5 or C 6 F 5 groups). Djerassi has argued that the a 2u orbital is actually lower in energy than the a 1u orbital in Zn­(TPFPP) , whereas this ordering is reversed in Zn­(TPP) . , However, recent calculations on Pd­(TPFPP) show the a 2u to be of higher energy than the a 1u orbital . Nevertheless, the precise ordering of these orbitals and their energy difference will be determined by a complicated mix of interactions involving the meso - substituent, metal based orbitals and the a 2u orbital.…”

Electron Withdrawing meso-Substituents Turn-on Magneto-Optical Activity in Porphyrins

“…Djerassi has argued that the a2u orbital is actually lower in energy than the a1u orbital in Zn(TPFPP), whereas this ordering is reversed in Zn(TPP). 43,47 However, recent calculations on Pd(TPFPP) show the a2u to be of higher energy than the a1u orbital. 48 Nevertheless, the precise ordering of these orbitals and their energy difference will be determined by a complicated mix of interactions involving the meso-substituent, metal based orbitals and the a2u orbital.…”