Electronic excited states of macrocyclic compounds: direct SAC-CI study

We developed the direct SAC-CI (symmetry-adapted cluster-configuration interaction) method for accurate calculations of electronic excited states of large molecules. The direct SAC-CI method uses an efficient MO (molecular orbital) direct scheme that is compatible with the perturbation-selection technique with using sparse linear algebra techniques. The direct SAC-CI can calculate large molecules with moderate computational cost. Using the direct SAC-CI method, excited states of free-base tetraazaporphyrin, phthalocyanine, naphthalocyanine, and anthracocyanine were studied. An interesting feature of the observed spectra is that the splitting of the Q-bands decreases with increasing molecular size. The SAC-CI calculation well reproduced the observed trend of excitation energies and showed the importance of electron correlation effects in the excited states