The effect on the electroche
mical oxidation and reduction potentials of 5,10,15,20-tetrakis(benzo-15-crown-5)porphyrin (TCP) and its
metal derivatives (MTCP; M = Mg(II), VO(IV), Co(II), Ni(II), Cu(II), Zn(II), Pd(II), Ag(II))upon potassiu
m ion induced di
merization of the porphyrins was syste
matically perfor
med in benzonitrile containing0.1 M (TBA)ClO
4 by differential pulse volta
mmetry technique. The HOMO-LUMO energy level diagra
m constructedfro
m the electroche
mical data revealed destabilization of the HOMO level and stabilization of the LUMO level upondi
mer for
mation while such a perturbation was larger for the HOMO level than the LUMO level. The geo
metry andelectronic structure of a representative ZnTCP and its di
mer, K
4(ZnTCP)
2, were evaluated by the ab initio B3LYP
method utilizing a
mixed basis set of 3-21G(*) for Zn, K, O, and N and STO-3G for C and H. The inter-porphyrinring distance of the di
mer calculated fro
m the opti
mized geo
metry agreed with the spectroscopically deter
minedone, and the calculated HOMO and LUMO frontier orbitals revealed delocalization on both of the porphyrins rings.The
metal-
metal distances calculated fro
m the triplet ESR spectra of the K
+ induced porphyrin di
mers bearingpara
magnetic
metal ions in the cavity followed the trend Cu-Cu < VO-VO < Ag-Ag. However, the spectral shiftsresulting fro
m the exciton coupling of the interacting porphyrin
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ms revealed no specific trend with respectto the
metal ion in the porphyrin cavity. Additionally, linear trends in the electroche
mically
measured HOMO-LUMO gap and the energy corresponding to the
most intense visible band of both MTCP and K
4(MTCP)
2 wereobserved. A reduced HOMO-LUMO gap predicted for the di
mer by B3LYP/(3-21G(*), STO-3G) calculations wasconfir
med by the results of optical absorption and electroche
mical studies.