title: Tuning the Electronic Properties of Acetylenic Fluorenes by Phosphaalkene Incorporation.
abstract: Versatile synthetic protocols for 2,7- and 3,6-diacetylenic fluorene-9-ylidene phosphanes (F9Ps) were developed. Protodesilylation of trimethylsilyl-protected acetylenic F9Ps affords terminal acetylenes that can be employed in Sonogashira and Glaser-type C-C coupling reactions to give thienyl-decorated and butadiyne-bridged fluorene-9-ylidene phosphanes, respectively. As evidenced by UV/Vis spectroscopy and cyclic voltammetry and corroborated by ab initio calculations, the presence of the P center in the F9Ps induces a significantly reduced HOMO-LUMO splitting that originates from stabilization of the LUMO levels. Variation of the acetylene substitution pattern is an additional tool to influence the optical and electronic properties. Whereas 3,6-disubstituted F9Ps have strong absorptions around 400 nm, mainly due to π-π* transitions, 2,7-diacetylenic F9Ps exhibit longest-wavelength absorptions that have significant charge-transfer character with an onset around 520 nm.
authors.affiliation: Department of Chemistry - Ångström Laboratory, Uppsala University, Box 523, 75120, Uppsala, Sweden.
authors.forename: Yurii V
authors.initials: YV
authors.lastname: Svyaschenko
authors.affiliation: Department of Chemistry - Ångström Laboratory, Uppsala University, Box 523, 75120, Uppsala, Sweden. Andreas.Orthaber@kemi.uu.se.
authors.forename: Andreas
authors.initials: A
authors.lastname: Orthaber
authors.affiliation: Department of Chemistry - Ångström Laboratory, Uppsala University, Box 523, 75120, Uppsala, Sweden. Sascha.Ott@kemi.uu.se.
authors.forename: Sascha
authors.initials: S
authors.lastname: Ott
keywords: alkynes; conjugation; electrochemistry; fluorenes; phospaalkenes