Porphin, molecular orbitals, energy

Chang and coworkers, using extended Huckel MO calculations provided an explanation for the easier oxidations and harder reductions as the porphyrin macrocycle is progressively reduced [93]. The calculated energy levels for the highest occupied (HOMO) and lowest unoccupied (LUMO) molecular orbitals of porphine, chlorin, iBC and BC complexes of Zn(II) are shown in Fig. 7. As the... 

Figure 6 The results of calculations on Mg porphin. The active molecular orbitals are shown in the upper part of the figure. Ae orbital energy...

Spiro and co-workers carried out an extensive study on resonance Raman spectra of various heme proteins. As is shown in Fig. 1-18, ferrocyiochrome c exhibits two electronic transitions referred to as the Qq (or a) and B (or Soret) bands along with a vibronic side band (Q or /S) in the 400-600cm region. According to MO (molecular orbital) calculations on the porphine core of symmetry, the Qa and B transitions result from strong interaction between the iH( J ) Cg(7r ) and a uiir) transitions which have similar energies... 

Porphyrins and their chlorin and bacteriochlorin derivatives provide numerous illustrations of the importance of configuration interactions [26], In porphin (Fig. 4.14, left), the highly symmetrical parent compound, the two highest filled molecular orbitals (t/i and 1/2 in order of increasing energy) are nearly isoenergetic, as are the two lowest unoccupied orbitals ( 03 and 1/4). The 0] —> 1/4 and 02 03... 

Fig. 4.14 Structures, energy diagrams, and excitations of poiphin, chlorin and bacteriochlorin. The horizontal bars are schematic representations of the energies of the highest two occupied molecular orbitals ( i and 2) and the first two unoccupied orbitals (V>3 and >4). relative to the energy of r/ij in each molecule. Arrows indicate excitations from one of the ocupied orbitals to an empty orbital, x and y correspond to the molecular axes shown as dotted lines with the porphin structure, and convey the symmetry of the product of the initial and final wavefunctions for each configuration, e.g., —> 4. Configurations with the same symmetry mix in the excited stales, and...

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