title: New 2,6-distyryl-substituted BODIPY isomers: synthesis, photophysical properties, and theoretical calculations.
abstract: A 2,6-distyryl-substituted boradiazaindacene (BODIPY) dye and a new series of 2,6-p-dimethylaminostyrene isomers containing both α- and β-position styryl substituents were synthesized by reacting styrene and p-dimethylaminostyrene with an electron-rich diiodo-BODIPY. The dyes were characterized by X-ray crystallography and NMR spectroscopy and their photophysical properties were investigated and analyzed by carrying out a series of theoretical calculations. The absorption spectra contain markedly redshifted absorbance bands due to conjugation between the styryl moieties and the main BODIPY fluorophore. Very low fluorescence quantum yields and significant Stokes shifts are observed for 2,6-distyryl-substituted BODIPYs, relative to analogous 3,5-distyryl- and 1,7-distyryl-substituted BODIPYs. Although the fluorescence of the compound with β-position styryl substituents on both pyrrole moieties and one with both β- and α-position substituents was completely quenched, the compound with only α-position substituents exhibits weak emission in polar solvents, but moderately intense emission with a quantum yield of 0.49 in hexane. Protonation studies have demonstrated that these 2,6-p-dimethylaminostyrene isomers can be used as sensors for changes in pH. Theoretical calculations provide strong evidence that styryl rotation and the formation of non-emissive charge-separated S1 states play a pivotal role in shaping the fluorescence properties of these dyes. Molecular orbital theory is used as a conceptual framework to describe the electronic structures of the BODIPY core and an analysis of the angular nodal patterns provides a reasonable explanation for why the introduction of substituents at different positions on the BODIPY core has markedly differing effects.
authors.affiliation: Key Laboratory of Organosilicon Chemistry and Material Technology, Ministry of Education, Hangzhou Normal University, Hangzhou, 310012 (P.R. China), Fax: (+86) 571-2886-8529; State Key Laboratory of Coordination Chemistry, Nanjing National Laboratory of Microstructures, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing, 210093 (P.R. China), Fax: (+86) 25-8331-4502.
authors.forename: Lizhi
authors.initials: L
authors.lastname: Gai
authors.forename: John
authors.initials: J
authors.lastname: Mack
authors.forename: Hua
authors.initials: H
authors.lastname: Lu
authors.forename: Hiroko
authors.initials: H
authors.lastname: Yamada
authors.forename: Daiki
authors.initials: D
authors.lastname: Kuzuhara
authors.forename: Guoqiao
authors.initials: G
authors.lastname: Lai
authors.forename: Zhifang
authors.initials: Z
authors.lastname: Li
authors.forename: Zhen
authors.initials: Z
authors.lastname: Shen
keywords: NMR spectroscopy; density functional calculations; dyes/pigments; fluorescence; photophysics; synthetic methods