title: Fluorescence properties of (E,E,E)-1,6-di(n-naphthyl)-1,3,5-hexatriene (n = 1, 2): effects of internal rotation.
abstract: The fluorescence spectroscopic properties of (E,E,E)-1,6-di(n-naphthyl)-1,3,5-hexatrienes (1, n = 1; 2, n = 2) have been investigated in solution and in the solid state. In solution, the absorption maxima (λ(a)) of the lowest-energy band (1, 374 nm; 2, 376 nm in methylcyclohexane) were similar for 1 and 2, whereas the fluorescence maxima (λ(f)) (1, 545 nm; 2, 453 nm) and quantum yields (φ(f)) (1, 0.046; 2, 0.68) were very different regardless of the solvent polarity. The fluorescence spectrum of 1 was independent of the excitation wavelength (λ(ex)), whereas the spectrum of 2 was weakly λ(ex)-dependent. In the solid state, the spectroscopic properties of 1 and 2 were similar (λ(a) = 437-438 nm, λ(f) = 496-505 nm, φ(f) = 0.04-0.07). The origins of emission are both considered to be mainly monomeric. With the help of single-crystal X-ray structure analysis and ab initio quantum chemical calculation, we conclude that the red-shifted and weak emission of 1 in solution originates from a planar excited state having small charge transfer character, reached from a twisted Franck-Condon state by the excited-state geometrical relaxation accompanied by the internal rotation around the naphthalene (Ar)-CH single bond. The similar fluorescence properties of 1 and 2 in the solid state can be attributed to the restriction of the geometrical relaxation. The effects of the Ar-CH rotational isomerism on the fluorescence properties in solution, for 2 in particular, are also discussed.
authors.affiliation: Electronics and Photonics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Higashi 1-1-1, Tsukuba, Ibaraki 305-8562, Japan. y.sonoda@aist.go.jp
authors.forename: Yoriko
authors.initials: Y
authors.lastname: Sonoda
authors.forename: Yukihiro
authors.initials: Y
authors.lastname: Shimoi
authors.forename: Midori
authors.initials: M
authors.lastname: Goto
authors.forename: Norimitsu
authors.initials: N
authors.lastname: Tohnai
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Kanesato
mesh_terms: D018360:Crystallography, X-Ray; D005453:Fluorescence; D008958:Models, Molecular; D015394:Molecular Structure; D009281:Naphthalenes / Q000737:chemistry*; D011090:Polyenes / Q000737:chemistry*; D011789:Quantum Theory; D012399:Rotation; D013050:Spectrometry, Fluorescence; D013237:Stereoisomerism
chemical_list: D009281:Naphthalenes; D011090:Polyenes