title: Communication: Tailoring the optical gap in light-harvesting molecules.
abstract: Systematically varying the optical gap that is associated with charge-transfer excitations is an important step in the design of light-harvesting molecules. So far the guidance that time-dependent density functional theory could give in this process was limited by the traditional functionals' inability to describe charge-transfer excitations. We show that a nonempirical range-separated hybrid approach allows to reliably predict charge-transfer excitations for molecules of practically relevant complexity. Calculated absorption energies agree with measured ones. We predict from theory that by varying the number of thiophenes in donor-acceptor-donor molecules, the energy of the lowest optical absorption can be tuned to the lower end of the visible spectrum. Saturation sets in at about five thiophene rings.
authors.affiliation: Theoretical Physics IV, University of Bayreuth, Bayreuth, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Karolewski
authors.forename: T
authors.initials: T
authors.lastname: Stein
authors.forename: R
authors.initials: R
authors.lastname: Baer
authors.forename: S
authors.initials: S
authors.lastname: Kümmel