Excited states and electronic spectra of extended tetraazaporphyrins.
Electronic excited states, electronic absorption, and magnetic circular dichroism (MCD) spectra of free-base tetraazaporphyrin (TAP), phthalocyanine (Pc), naphthalocyanine (Nc), and anthracocyanine (Ac) were studied by quantum chemical calculations using the symmetry-adapted cluster-configuration interaction (SAC-CI) method. Not only optically allowed states including the Q- and B-bands but also optically forbidden states were calculated for transitions whose excitation energies were lower than 4.5 eV. The present SAC-CI calculations consistently assigned the absorption and MCD peaks as optically allowed π→π(∗) excitations, although these calculations using double-zeta basis limit quantitative agreement and discussion. For Nc and Ac, excited states beyond the four-orbital model appeared in the low-energy region. The low-energy shifts of the Q-bands with the extension of molecular size were explained by the orbital energies. The splitting of the Q-bands decreases with extension of the molecular size. This feature was reproduced by the SAC-CI calculations but the configuration interaction with single excitations and time-dependent density functional theory calculations failed to reproduce this trend. Electron correlation in the excited states is important in reproducing this splitting of the Q-bands and in describing the energy difference between the B(2u) and B(3u) states of free-base porphyrins.
Department of Theoretical and Computational Molecular Science, Institute for Molecular Science, 38 Nishigo-Naka, Myodaiji, Okazaki 444-8585, Japan. fukuda@ims.ac.jp
Ryoichi
R
Fukuda
Masahiro
M
Ehara
Hiroshi
H
Nakatsuji
D002942:Circular Dichroism / Q000379:methods*; D004563:Electrochemistry; D004583:Electrons / Q000145:classification; D007211:Indoles / Q000737:chemistry*; D054833:Isoindoles; D046032:Microscopy, Energy-Filtering Transmission Electron / Q000379:methods; D011166:Porphyrins / Q000737:chemistry*; D013053:Spectrophotometry / Q000379:methods*
D007211:Indoles; D054833:Isoindoles; D011166:Porphyrins; C013647:phthalocyanine