title: Tuning the electronic coupling in a low-bandgap donor-acceptor copolymer via the placement of side-chains.
abstract: We present a spectroscopic and theoretical investigation of the effect of the presence and position of hexyl side-chains in the novel low-bandgap alternating donor-acceptor copolymer poly[bis-N,N-(4-octylphenyl)-bis-N,N-phenyl-1,4-phenylenediamine-alt-5,5'-4',7',-di-2-thienyl-2',1',3'-benzothiadiazole] (T8TBT). We use electronic absorption and Raman spectroscopic measurements supported by calculations of chain conformation, electronic transitions, and Raman modes. Using these tools, we find that sterically demanding side-chain configurations induce twisting in the electronic acceptor unit and reduce the electronic interaction with the donor. This leads to a blue-shifted and weakened (partial) charge-transfer absorption band together with a higher photoluminescence efficiency. On the other hand, sterically relaxed side-chain configurations promote coupling between donor and acceptor units and exhibit enhanced absorption at the expense of luminescence efficiency. The possibility of tuning the donor-acceptor character of conjugated polymers by varying the placement of side-chains has very important ramifications for light emitting diode, Laser, display, and photovoltaic device optimization.
authors.affiliation: Cavendish Laboratory, J J Thomson Avenue, Cambridge CB3 0HE, United Kingdom.
authors.forename: Philipp M
authors.initials: PM
authors.lastname: Oberhumer
authors.forename: Ya-Shih
authors.initials: YS
authors.lastname: Huang
authors.forename: Sylvain
authors.initials: S
authors.lastname: Massip
authors.forename: David T
authors.initials: DT
authors.lastname: James
authors.forename: Guoli
authors.initials: G
authors.lastname: Tu
authors.forename: Sebastian
authors.initials: S
authors.lastname: Albert-Seifried
authors.forename: David
authors.initials: D
authors.lastname: Beljonne
authors.forename: Jérôme
authors.initials: J
authors.lastname: Cornil
authors.forename: Ji-Seon
authors.initials: JS
authors.lastname: Kim
authors.forename: Wilhelm T S
authors.initials: WT
authors.lastname: Huck
authors.forename: Neil C
authors.initials: NC
authors.lastname: Greenham
authors.forename: Justin M
authors.initials: JM
authors.lastname: Hodgkiss
authors.forename: Richard H
authors.initials: RH
authors.lastname: Friend