title: Optical excitations in star-shaped fluorene molecules.
abstract: A detailed study of the low-energy optical transitions in two families of star-shaped molecules is presented. Both families have 3-fold rotational symmetry with oligofluorene arms attached to a central core. In one family, the core of the molecule is a rigid meta-linked truxene, while the other is a meta-linked benzene moiety. The low-energy transitions were studied both experimentally and using time-dependent density functional theory (TD-DFT). The optical transitions of these new star-shaped molecules were compared with corresponding linear oligofluorenes. Both families of star-shaped molecules showed higher absorption and fluorescence dipoles and photoluminescence quantum yields than straight chain oligofluorenes. TD-DFT calculations show that absorption takes place across the entire molecule, and after excited state relaxation, the emission results from a single arm. In both theory and experiment the transition dipole moments show an approximate n(0.5) dependence on the number of fluorene units in each arm.
authors.affiliation: Organic Semiconductor Centre, SUPA, School of Physics and Astronomy, University of St. Andrews, North Haugh, St. Andrews, Fife, KY16 9SS, United Kingdom.
authors.forename: Neil A
authors.initials: NA
authors.lastname: Montgomery
authors.forename: Jean-Christophe
authors.initials: JC
authors.lastname: Denis
authors.forename: Stefan
authors.initials: S
authors.lastname: Schumacher
authors.forename: Arvydas
authors.initials: A
authors.lastname: Ruseckas
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Skabara
authors.forename: Alexander
authors.initials: A
authors.lastname: Kanibolotsky
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Paterson
authors.forename: Ian
authors.initials: I
authors.lastname: Galbraith
authors.forename: Graham A
authors.initials: GA
authors.lastname: Turnbull
authors.forename: Ifor D W
authors.initials: ID
authors.lastname: Samuel
mesh_terms: D005449:Fluorenes / Q000737:chemistry*; D049449:Luminescence; D008958:Models, Molecular; D015394:Molecular Structure; D011789:Quantum Theory
chemical_list: D005449:Fluorenes