Deciphering Charge-Transfer and Triplet-Multiplet Excited States in Substituted MnIII and CrIII Phthalocyanines: Insights from UV-Vis-NIR, MCD, and Theory
Year: 2026
Type: preprint
Abstract: Charge-transfer (metal-to-ligand, MLCT, ligand-to-metal, LMCT, and interligand, (LLCT) and intraligand (π−π* and triplet-multiplet) transitions observed in the UV-vis-NIR and magnetic circular dichroism (MCD) spectra of high-spin Pc tBu Cr III Cl, Pc tBu Mn III Cl, and Pc OBu Mn III Cl (Pc tBu is the dianion of the 2,9(10),16(17),23(24)-tetra-tert-butyl-phthalocyanine and Pc OBu is the dianion of the 1,4,8,11,15,18,22,25-octa-n-butoxy-phthalocyanine) complexes were analyzed with the help of group theory combined with time-dependent density functional theory and ab initio (CASSCF and NEVPT2(13e,14o)) calculations. The energy shift between tert-butylated and butoxylated Pc rings, the energy shift between Mn and Cr centers, and the change in solvent donicity between dichloromethane/chloroform (DCM / CHCl 3 ) and N,N-dimethylformamide (DMF) were used to systematically perturb the energies of electronic transitions. It was demonstrated that the triplet-multiplet transitions dominate the NIR region of the UV-vis-NIR and MCD spectra, while LMCT bands dominate the “phthalocyanine window” (350-550 nm) region of the UV-vis-NIR and MCD spectra. Like other trivalent transition-metal phthalocyanines, MLCT transitions were predicted in the UV region of the UV-vis-NIR and MCD spectra. General trends in triplet-multiplet transitions across d 1 -d 9 configurations as well as the function of axial ligands for a given metal are delineated and parameterized. These studies will be used for further understanding of wavelength-dependent photochemical activity and the effects of structural substitutions on electrocatalytic and photocatalytic transformations.
Source: ChemRxiv
Institutions: University of Tennessee at Knoxville, Simon Fraser University
Language: English
Subfield: Materials Chemistry
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7213769119