title: Highly fluorescent flavins: rational molecular design for quenching protection based on repulsive and attractive control of molecular alignment.
abstract: Unprecedented intense fluorescent emission was observed for a variety of flavin compounds bearing a perpendicular cyclic imide moiety at the C7 position of an isoalloxazine platform. A series of alloxan-substituted flavins was prepared selectively by reduction of the corresponding N-aryl-2-nitro-5-alkoxyanilines with zinc dust and subsequent reaction with alloxan monohydrate in the presence of boric acid. Analogues bearing oxazolidine-2,4-dione functionality were obtained on methylation of the alloxan-substituted flavins with methyl iodide and subsequent rearrangement in the presence of an inorganic base. The flavin compounds exhibit intense white-green fluorescent emission in the solution state under UV excitation at 298 K, with emission efficiencies Φ298 K greater than 0.55 in CH3 CN, which are higher than the values for all reported flavin compounds under similar conditions. The highest Φ298 K value of 0.70 was obtained in CH3 CN for isoalloxazine bearing C7-alloxan and N10-2,6-diisopropylphenyl groups. The temperature dependence of the emission intensities indicates that the pronounced emission properties at 298 K are attributable to the highly heat resistant properties towards emission decay with increasing temperature. Mechanistic studies, including X-ray diffraction analysis, revealed that the good emission properties and high heat resistance of the alloxan-substituted flavins are due to a synergetic effect of the associative nature of the C7-alloxan unit and the repulsive nature of the perpendicular bulky substituents at the C7 and N10 positions.
authors.affiliation: Department of Chemistry, Graduate School of Engineering Science, Osaka University, Machikaneyama, Toyonaka, Osaka 560-8531 (Japan).
authors.forename: Haruka
authors.initials: H
authors.lastname: Suzuki
authors.affiliation: Department of Chemistry, Graduate School of Engineering Science, Osaka University, Machikaneyama, Toyonaka, Osaka 560-8531 (Japan).
authors.forename: Ryo
authors.initials: R
authors.lastname: Inoue
authors.affiliation: Department of Chemistry, Graduate School of Engineering Science, Osaka University, Machikaneyama, Toyonaka, Osaka 560-8531 (Japan).
authors.forename: Soichiro
authors.initials: S
authors.lastname: Kawamorita
authors.affiliation: Department of Chemistry, Graduate School of Engineering Science, Osaka University, Machikaneyama, Toyonaka, Osaka 560-8531 (Japan).
authors.forename: Naruyoshi
authors.initials: N
authors.lastname: Komiya
authors.affiliation: Department of Chemistry, Graduate School of Engineering Science, Osaka University, Machikaneyama, Toyonaka, Osaka 560-8531 (Japan).|Present address: Department of Chemical Science and Technology, Institute of Technology and Science, Tokushima University, Minamijosanjima, Tokushima 770-8506 (Japan).
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Imada
authors.affiliation: Department of Chemistry, Graduate School of Engineering Science, Osaka University, Machikaneyama, Toyonaka, Osaka 560-8531 (Japan). naota@chem.es.osaka-u.ac.jp.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Naota
mesh_terms: D000496:Alloxan / Q000737:chemistry*; D000814:Aniline Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D005415:Flavins / Q000737:chemistry*; D005456:Fluorescent Dyes / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D014961:X-Ray Diffraction
chemical_list: D000814:Aniline Compounds; D005415:Flavins; D005456:Fluorescent Dyes; C008173:isoalloxazine; D000496:Alloxan
keywords: flavins; fluorescence; hydrogen bonds; molecular design; steric hindrance