Transient resonance Raman spectroscopic studies of some paramagnetic metalloporphyrins: effects of axial ligand on charge-transfer and photoreduction processes

Abstract

The presence of odd electrons in d-orbitals of the central metal ions of these metalloporphyrins gives rise to a strong interaction with porphyrin p-electronic system, which affects the energy relaxation pathways of their photoexcited states. The formation and energy of porphyrin $ metal (p,d) or (d,p * ) charge-transfer (CT) and metal (d,d) states are sensitive to the solvents employed, especially to the axial ligation ability of the solvents. Based on the change in Raman wavenumbers induced by the structural change in the exciplex formation of photoexcited Cu II TPP with the solvents, two intermediate ( p,d) CT states below the 2 T/ 4 T (p,p * ) states are proposed, one being less affected by the ligating solvent (CT 1 ; Cu II porphyrins * ) and the other strongly influenced by a s-donor axial ligand [CT 2 ; Cu II porphyrins * (ligand)]. As for XCr III TPP (X = Cl or Br), the photodissociation of axial ligand halogen atoms was observed in benzene.On the other hand, in THF upon photoexcitation, the axial ligand halogen atoms were replaced by the solvent molecules to form the five-coordinate Cr III TPP(THF). A significant reduction in the lifetimes of photoexcited ClCr III TPP in THF was observed, which is probably due to the participation of the low-lying (p,d p ) CT state in the energy relaxation of the five-

Extraction of hydrophobic analytes from organic solution into a titanate 2D-nanosheet host: Electroanalytical perspectives

“…The latter group of peaks could be related to Raman peaks observed previously in organic solution [46]. The band at 1350 cm À1 could be related to data reported for resonance Raman measurements in different solvents [47].…”

Electrochemically Triggered Dynamics Within a Hybrid Metal-Organic Electrocatalyst

“…Thus, the Mn(III) to Mn(II) transition could potentially involve the loss of an axial ligand. [34][35] Component fit analysis 36 of the spectral series revealed that there were indeed two species present in the spectra that interconverted at -0.8V, matching the observations from UV-Vis absorbance (Fig. 3c).…”

Electrochemically Triggered Dynamics within a Hybrid Metal–Organic Electrocatalyst

“…The ν 8 mode was found at 378 cm –1 and matches well with the frequency expected for Mn­(II) porphyrin in the absence of axial coordination. Thus, the Mn­(III) to Mn­(II) transition can involve the loss of an axial ligand. , The detachment of the fifth ligand bound to the oxidized Mn is also corroborated by disappearance of bands in the low-frequency region below 500 cm –1 upon reduction. This frequency window typically reflects metal–ligand (M–L) vibrations such as the aforementioned ν 8 (Mn–N).…”

“…This frequency window typically reflects metal–ligand (M–L) vibrations such as the aforementioned ν 8 (Mn–N). For example, loss of a chloride ligand in Mn tetraphenyl porphyrins was successfully monitored via the decay of the ν­(Mn–Cl) vibration located at around 270–300 cm –1 . , In this respect, the bands at 223 and 241 cm –1 could represent Mn–L vibrations in the present system and were found to disappear upon formation of Mn­(II) (Figure S7, SI). Though bands at 283 and 343 cm –1 also significantly decrease in intensity, they can still be visibly detected in the Mn­(II) spectrum, suggesting that they are present in both systems and the lower intensity arises from the lower resonance enhancement of the reduced species.…”