Details

Autor(en) / Beteiligte

• Miwa, Hideya
• Makarova, Elena A.
• Ishii, Kazuyuki
• Luk'yanets, Evgeny A.
• Kobayashi, Nagao

Titel

Spectroscopy, Electrochemistry, and Molecular Orbital Calculations of Metal‐Free Tetraazaporphyrin, ‐chlorin, ‐bacteriochlorin, and ‐isobacteriochlorin

Ist Teil von

• Chemistry : a European journal, 2002-03, Vol.8 (5), p.1082-1090

Ort / Verlag

Weinheim: WILEY‐VCH Verlag GmbH

Erscheinungsjahr

2002

Link zum Volltext

Quelle

Wiley Online Library - AutoHoldings Journals

Beschreibungen/Notizen

• Metal‐free tetraazachlorin (TAC), ‐bacteriochlorin (TAB), and ‐isobacteriochlorin (TAiB) were characterized by electronic absorption, magnetic circular dichroism (MCD), fluorescence, and time‐resolved ESR (TR‐ESR) spectroscopy, and by cyclic voltammetry. The results are compared with those of metal‐free tetraazaporphyrin (TAP). The potential difference ΔE between the first oxidation and reduction couples decreases in the order TAP>TAiB>TAC>TAB. The splitting of both the Q and Soret bands decreases in the order TAB>TAC>TAP>TAiB. Corresponding to the split absorption bands, MCD spectra show a minus‐to‐plus pattern with increasing energy in both the Q and Soret regions, which suggests that the energy difference between the HOMO and second HOMO is larger than that between the LUMO and second LUMO. These spectroscopic properties and redox potentials were reproduced by molecular orbital calculations using the ZINDO/S Hamiltonian. The fluorescence quantum yields of the reduced species are much smaller than that of TAP. The zero‐field splitting (ZFS) parameters D and E of the excited triplet states (T1) of these species decrease and increase, respectively, on going from TAP to TAC and further to TAB. The D and E values of TAiB are larger than those of the other species. The results are supported by the absence of interaction between the spin over reduced pyrrole moieties of the HOMO and over the LUMO, and by calculations of ZFS under a half‐point‐charge approximation. The hydrogenated pyrrole moieties in tetraazachlorin, ‐bacteriochlorin, and ‐isobacteriochlorin (TAiB) lower the extent and symmetry of their π‐electron systems and thus influence their physicochemical properties, which were characterized by electronic absorption, magnetic circular dichroism, fluorescence, and time‐resolved ESR spectroscopy, and by cyclic voltammetry. The data are compared with those of tetraazaporphyrin (TAP).