Saddle distortion of a sterically unhindered porphyrin ring in a copper porphyrin with electron-donating substituents

Two crystalline porphyrins, CuT(4′-OMePh)P (1) and H ₂T(4′-OMePh)P (2) (T(4′-OMePh)P^2- = 5, 10, 15,20-tetrakis(4-methoxyphenyl)-21H,23H-porphyrin dianion), have been synthesized and characterized by a single-crystal X-ray diffraction. Compound 1 is crystallized in the orthorhombic system with a space group of Pna2 ₁, but compound 2 is crystallized in the monoclinic system with a space group of P2/c. Compound 1 is characterized as an isolated structure with a saddle-distorted nonplanar porphyrin macrocycle and an embedded cupric ion coordinating to four pyrrole nitrogen atoms. Nonmetalated compound 2 also displays an isolated structure, but the macrocycle of porphyrin is close to a perfect plane. The molecules in 2 are interconnected through five C-HA·A·A·π hydrogen bonding interactions to yield a 3-D supramolecular network. However, the molecules in 1 are interlinked via five C-HA·A·A·π interactions and two C- HA·A·A·O hydrogen bonding interactions to yield a more complex 3-D supramolecular motif. The two more C-HA·A·A·O hydrogen bonding interactions are attributed to the distortion of porphyrin macrocycle, resulting from the metalation. The metalation brought changes not only in the crystal structures and supramolecular motifs but also in the properties. The photophysical and redox properties of 1 and 2 in solution have also been studied by steady-state absorption and fluorescence, cyclic voltammetry, fluorescence lifetime and nanosecond transient absorption techniques.