Theoretical investigations of the electronic states of porphyrins. IV. Low‐lying electronic states of bisammineporphinatoiron(II)

Ab initio CI calculations are reported on the lowest quintet, triplet, and singlet states of Fe II (P) (NH 3 ) 2 . The lowest singlet state has strong mixing between the configuration ( d xy 2 ( d π ) 4 and ( d xy ) 2 ( d π ) 3 e g π*. The lowest quintet is mixed between 6 A 1 g ) d π and ( 6 A 1 g )e g π*, where 6 A 1 g refers to the high‐spin ferric configuration. We calculate many low‐energy states as 3 (π→π*) ring and metal triplet and quintet configurations [“triptriplets” and “tripquintets”]. The calculations also show low‐energy charge‐transfer configurations of ring anion excited quartets and ferric quartets and sextets [“quartquartets” and “quartsextets”]. The farthest red x,y ‐polarized bands of the experimental spectra of low‐spin hemoproteins are identified as d xy → e g π* or d π → d   z   2mixed with d π → d   x   2 ‐ y   2and the z ‐polarized bands are assigned as d π → e g π*. The farthest red x,y ‐polarized bands of the high‐spin hemoproteins are identified as excited quartsextet states. Picosecond transients observed in Fe II (TPP) (pip) 2 are attributed to an initial 1 ( d π → e g π*) state, which inter‐system crosses to high‐spin states that lose one ligand.