Investigation of Ferrocene Linkers in β-Substituted Porphyrins

A series of β-ferrocene-modified zinc porphyrins, with various electron-withdrawing units appended to the ferrocene, were synthesized, and their electronic properties were investigated. The ferrocene was able to be modified with the substituents, with its oxidation potential increased by up to 0.3 V, without significantly perturbing the porphyrin core. A small red-shift of the strongest absorption band (B band) occurred upon the addition of the electron-withdrawing substituents (270 cm^-1), occurring alongside a broadening of the band. The singlet state is unaffected by the ferrocene substitution; however, the triplet state lifetimes are decreased by 10.4-10.6 μs from that of the unsubstituted ferrocene porphyrin (18.1 μs). Computational studies showed that the changes in the optical properties are due to a loss of degeneracy of the porphyrin lowest unoccupied molecular orbitals; this is supported by resonance Raman spectroscopy studies, which show different enhancement patterns when probing the high- and low-energy edges of the B band.