title: Solid-emissive fluorophores constructed by a non-planar heteropolycyclic structure with bulky substituents: synthesis and X-ray crystal structures.
abstract: Novel solid-emissive indeno[1,2-b]benzo[4,5-e]pyran-11-one-type fluorophores having non-planar structures with sterically hindered substituents (R = butyl, phenyl, and thienyl) have been designed and conveniently synthesized. The fluorescence quantum yields of in 1,4-dioxane were (Phi = 0.053) >> (Phi = 0.013) > (Phi = 0.003). On the other hand, the solid-state fluorescence quantum yields of the fluorophores were (Phi = 0.39) > (Phi = 0.15) > (Phi = 0.06). To elucidate the large differences in the quantum yields in solution and in the solid state and among the fluorophores , we performed time-resolved fluorescence spectroscopic measurements, semi-empirical molecular orbital calculations (AM1 and INDO/S), and X-ray crystallographic analyses of . The comparison of the values of the radiative and non-radiative rate constants determined by the time-resolved spectroscopic measurements in solution and in the crystalline state supported that non-radiative decay is reduced by restriction of the rotation of the phenyl and thienyl rings in the solid state. In addition, the X-ray crystal structures demonstrated that, in and , the non-planar structure with sterically hindered substituents prevents the fluorophores from forming short pi-pi contacts and produces strong solid-state fluorescence. On the other hand, in the crystal of , the formation of continuous intermolecular CH[dot dot dot]S bonding between neighboring fluorophores was found to increase short pi-pi contacts and reduce the fluorescence intensity.
authors.affiliation: Department of Material Science, Faculty of Science, Kochi University, Akebono-cho, Kochi 780-8520, Japan.
authors.forename: Yousuke
authors.initials: Y
authors.lastname: Ooyama
authors.forename: Shintaro
authors.initials: S
authors.lastname: Yoshikawa
authors.forename: Shigeru
authors.initials: S
authors.lastname: Watanabe
authors.forename: Katsuhira
authors.initials: K
authors.lastname: Yoshida
mesh_terms: D001578:Benzopyrans / Q000737:chemistry*; D003198:Computer Simulation; D018360:Crystallography, X-Ray; D005456:Fluorescent Dyes / Q000138:chemical synthesis* / Q000737:chemistry*; D007189:Indans / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D015394:Molecular Structure; D011789:Quantum Theory; D012680:Sensitivity and Specificity; D013050:Spectrometry, Fluorescence / Q000379:methods
chemical_list: D001578:Benzopyrans; D005456:Fluorescent Dyes; D007189:Indans