| Abstract
| - Electroabsorption and electrofluorescence spectroscopies were conducted for tri-9-anthrylborane (TAB) dopedin poly(methyl methacrylate) films (1.0 mol %) to reveal the spectroscopic and excited-state properties of thecompound. TAB showed three distinct absorption bands: bands I [(19 − 25) × 103 cm-1], II [(25−31) ×103 cm-1], and III (>31 × 103 cm-1). The electroabsorption spectrum demonstrated that the electronic transitionsin bands I and III accompanied electric dipole moment changes (Δμ), while the change in the molecularpolarizability contributed mainly to electroabsorption band II. Because of the similarities of the electroabsorptionspectrum of band II with that of anthracene itself, band II was assigned to the electronic transition to thelocally excited (LE) state of the anthryl group. On the other hand, bands I and III were best described by theelectronic transitions to the excited charge-transfer (CT) states. The study demonstrated furthermore that theΔμ value of TAB accompanied by the lowest-energy electronic transition was as large as 7.8 D, which agreedvery well with that determined by the solvent dependences of the absorption and fluorescence maximumenergies of TAB (∼8.0 D, ref 1): Δμ = 7.8−8.0 D. The results proved explicitly that the excited state ofTAB was localized primarily on the p orbital of the boron atom. Despite the dipole moment change (Δμ =7.8−8.0 D) for the lowest-energy electronic transition (band I), the electrofluorescence of TAB accompaniedthe change in the molecular polarizability. The spectroscopic and excited-state properties of TAB includingthe curious behavior of the electrofluorescence spectrum as mentioned above were discussed on the basis oftheoretical considerations.
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