Application of the Perimeter Model to the Assignment of the Electronic Absorption Spectra of Gold(III) Hexaphyrins with [4n+2] and [4n] π‐Electron Systems

Abstract

The electronic excited states of two forms of meso-hexakis(pentafluorophenyl)-substituted gold(III) hexaphyrin(1.1.1.1.1.1) have been investigated by density functional calculations and magnetic circular dichroism (MCD) spectroscopy, in order to assign their low-energy excited singlet states. We found that the perimeter model can be successfully applied to the interpretation of the electronic states. In the case of the neutral forms (Au(2)-N, Au-N), the absorption bands observed in the NIR and visible region can be assigned to pi-pi* transitions referred to as the L and B bands, respectively, analogous to the Q and Soret bands of regular porphyrins. In marked contrast with the neutral forms, the absorption bands of the reduced forms (Au(2)-R and Au-R) are attributed to pi-pi* transitions involving six frontier molecular pi orbitals. By applying the 4N-electron perimeter model, the six orbitals are labeled as h(-), h(+), s(-), s(+), l(-), and l(+), while the observed absorption bands can be assigned to the S, N(1), N(2), P(1), and P(2) transitions, in order of increasing energy.

Gram‐Scale Synthesis of Nickel(II) Norcorrole: The Smallest Antiaromatic Porphyrinoid

“…[14] The MCD spectrum of 2 (Figure 2 a) exhibits the spectral features of antiaromatic compounds; very weak bands with a forbidden nature in the lower energy region and clear Faraday B terms at 521 and 431 nm, indicating that 2 possesses an antiaromatic conjugation system with a closed-shell ground state, as is suggested by NMR spectroscopy. Allowed bands of antiaromatic compounds comprise four HOMO!SOMO (h À !s + and h + !s + ) and SOMO!…”

Rectangular-Shaped Expanded Phthalocyanines with Two Central Metal Atoms

“…In addition, the theoretical absorption spectrum ( Figure 6) and a molecular orbital (MO) diagram ( Figure 8) were calculated for Opt2A using time-dependent density functional theory (TD-DFT) (B3LYP/6-31G(d) for C, H, N, and O and LANL2DZ for Mo) 28 and compared with those of substituentfree H 2 Pc. The symmetry-split Q bands of Opt2A were Figure 6).…”

Boron(III) Induced Skeletal Rearrangement of Hexaphyrin(1.1.1.1.1.1) to Hexaphyrin(2.1.1.0.1.1)

“…[13] Distinct bond-length alternation along the 28p electron circuit is also apparent. [5,16] Cyclic voltammetry measurement revealed reversible oxidation potentials at 0.24 and 0.54 V (vs. Fc/Fc + ; Fc= [(C 5 H 5 ) 2 Fe]) and reduction potentials at À0.67 and À1.07 V, hence indicating a small electrochemical HOMO-LUMO gap (0.91 V), which is characteristic of antiaromatic species (Supporting Information). The formation of 4 requires a drastic and unprecedented skeletal rearrangement, namely the transposition of an aryl-substituted mesoposition over pyrrole units.…”

“…Bond lengths of the directly connected a-a carbon bond and the central bond in the s-trans 1,3-butadienyl linkage are 1.46 and 1.45 , respectively, which are similar to that of the central C À C bond of 1,3-butadiene (1.48 ). [16] The weakness of antiaromaticity may be ascribed to the large dihedral angle (728) between directly linked bipyrrole unit. The mechanism of this rearrangement is still not settled, but is considered to involve the formation of a-a and meso-meso bonds and the subsequent cleavage of two meso-a bonds (Scheme 3 and Supporting Information).…”