title: Effect of periodic replacement of the heteroatom on the spectroscopic properties of indole and benzofuran derivatives.
abstract: The electronic structures of a homologous series of indole and benzofuran derivatives, in which the nitrogen or oxygen atom is replaced by group 15 and group 16 heavier heteroatoms, have been investigated by means of various spectroscopic techniques coupled with density functional calculations. It was found that the excitation energies of the group 16 benzoheteroles systematically shift to the red in the order of benzofuran (6), benzothiophene (7), benzoselenophene (8), and benzotellurophene (9). In contrast, the electronic absorption spectra of the group 15 benzoheteroles, 1-phenyl derivatives of indole (1b), phosphindole (2b), arsindole (3b), stibindole (4b), and bismuindole (5b), did not exhibit this type of spectral shift. X-ray analysis and density functional theory (DFT) studies revealed that 2b-5b adopt a bent conformation both in the crystalline and in the solution phases. In contrast, planar structures were calculated for the group 16 heterocycles. Using the observed spectroscopic properties and time-dependent density functional theory (TDDFT) calculations, the electronic absorption spectra of the present heterocycles were assigned. A molecular orbital analysis was performed to rationalize the effect of replacement of the heteroatom on the electronic structures. The observed magnetic circular dichroism (MCD) sign patterns of these heterocycles are interpreted according to Michl's perimeter model.
authors.affiliation: Advanced Elements Chemistry Laboratory, the Institute of Physical and Chemical Research (RIKEN), Wako-shi, Saitama, Japan. atsuya-muranaka@riken.jp
authors.forename: Atsuya
authors.initials: A
authors.lastname: Muranaka
authors.forename: Shuji
authors.initials: S
authors.lastname: Yasuike
authors.forename: Ching-Yuan
authors.initials: CY
authors.lastname: Liu
authors.forename: Jyoji
authors.initials: J
authors.lastname: Kurita
authors.forename: Naoki
authors.initials: N
authors.lastname: Kakusawa
authors.forename: Takashi
authors.initials: T
authors.lastname: Tsuchiya
authors.forename: Masako
authors.initials: M
authors.lastname: Okuda
authors.forename: Nagao
authors.initials: N
authors.lastname: Kobayashi
authors.forename: Yotaro
authors.initials: Y
authors.lastname: Matsumoto
authors.forename: Kengo
authors.initials: K
authors.lastname: Yoshida
authors.forename: Daisuke
authors.initials: D
authors.lastname: Hashizume
authors.forename: Masanobu
authors.initials: M
authors.lastname: Uchiyama
mesh_terms: D000042:Absorption; D001572:Benzofurans / Q000737:chemistry*; D002942:Circular Dichroism; D018360:Crystallography, X-Ray; D004583:Electrons; D007211:Indoles / Q000737:chemistry*; D008280:Magnetics; D011789:Quantum Theory; D013997:Time Factors
chemical_list: D001572:Benzofurans; D007211:Indoles; C105430:benzofuran