Charge-transfer states, porphyrin

Quantum Mechanical Studies of Charge-Transfer States in Porphyrin Heterodimers... 

PETKE AND MAGGIORA Charge-Transfer States in Porphyrin Hetewdimers 25... 

The large number of electronic configuration of iron porphyrins with oxidative states of 2+ or 3+, high and low spin forms, and charge transfer states with different axial ligands offer the possibility of a number of non-radiative decay pathways ( ). In... 

Copper-reconstituted cytochrome c ( cyt-c) has also been investigated with transient absorption methods (49). No evidence of ghotoinduced ejection of the fifth ligand is observed in either cyt-c or the model Cu-porphyrin 5-coordinate complexes (60-62). This is consistent with the likely transient state being a non-dissociative w w or d 2 2 charge-transfer state. 

Magnesium porphine-porphines See also Porphyrins charge transfer states, 20-50 description, photodynamic role of triplet states, 42-44 dipole moments, 31-35 effect of added chloride ion, 39-42... 

Braterman, Davies and Williams (44) considered the possibility of configuration interaction between the porphyrin n states and the charge transfer states. According to the four-orbital model of Gouterman, discussed in Section IIB, the Soret and a— excited states are of Eu symmetry. The only allowed charge transfer transitions are from the porphyrin a u and aexcited states, and from the porphyrin a2u orbital to the metal... 

Analysis of the UV-visible, ESR and redox potential data suggests the absence of any exciton couphng between the porphyrin rings and these trimers. Energies of the singlet and charge transfer states are shown in Figure 1. H2 means H2L , Ge means [(L ) Ge (0H)2] and Zn means ML M . 

Photocatalytic CO2 reduction of a supramolecule with a Zn porphyrin unit, which is a redox photosensitizer that can absorb even wider ranges of visible light, connected to a rhenium complex (ZnTMP-ReCl) was considered (101,102). In this system, ultrafast (l.SxlO s ) electron transfer from the S2 excited state of the ZnTMP unit to the rhenimn imit was observed. Reduction of CO2 proceeded with generation of the OER species of the rhenium unit by the reduction of this intramolecular charge-transfer state by TEA. 

Experimentally, this imphes that selective excitation of the two types of chromophores is feasible (e.g., 100% FBI at 585 mn, 62% Ru(TPP)(CO) at 530 nm). The energy level diagram of 16 (Fig. 35) can be considered as a simple superposition of those of the separated constituents, with the addition of a charge transfer state in which PBI is reduced and the Ru porphyrin is oxidized (energy estimated from electrochemistry). 

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