Hybrid Density Functional Theory (DFT) Study on Electronic States of Halogen-Substituted Organic-Inorganic Hybrid Compounds: Al-NTCDA

摘要

Hybrid density functional theory (DFT) calculations have been carried out for high-performance molecular devices, complexes of naphthalene tetracarboxylic dianhydride (NTCDA) and halogen-substituted NTCDA with aluminum (denoted by Al_4(X)_4NTCDA, where X denotes H, F, Cl or Br). The four hydrogen atom of NTCDA were substituted with X atoms. It was found that the electronic state of the complex in the ground state is composed of a charge-transfer state expressed by (Al_4)~(δ+)((X)_4NTCDA)~(δ-). Also, it was predicted that the binding energy of the Al atom was enhanced by the halogen substitution, indicating that the complex of (X)_4NTCDA (X = halogen atoms) is more stable in terms of energy than that of pure NTCDA (X = H). The large binding energy results in the high material stability in atmosphere. By photoirradiation of the complex, the interaction between Al and NTCDA was changed from ionic to covalent. This electronic excitation was assigned to the back donation of an electron from NTCDA to Al, and it was predicted theoretically that the absorption spectrum appears as a charge-transfer (CT) band in the near infrared region. The effects of halogen-substitution on the electronic states of NTCDA are discussed on the basis of theoretical results.