title: Two's Company, Three's a Crowd: Exciton Localization in Cofacially Arrayed Polyfluorenes.
abstract: Understanding the mechanisms of long-range energy transfer through polychromophoric assemblies is critically important in photovoltaics and biochemical systems. Using a set of cofacially arrayed polyfluorenes (Fn), we investigate the mechanism of (singlet) exciton delocalization in π-stacked polychromophoric assemblies. Calculations reveal that effective stabilization of an excimeric state requires an ideal sandwich-like arrangement; yet surprisingly, emission spectroscopy indicates that exciton delocalization is limited to only two fluorene units for all n. Herein, we show that delocalization is determined by the interplay between the energetic gain from delocalization, which quickly saturates beyond two units in larger Fn, and an energetic penalty associated with structural reorganization, which increases linearly with n. With these insights, we propose a hopping mechanism for exciton transfer, based upon the presence of multiple excimeric tautomers of similar energy in larger polyfluorenes (n ≥ 4) together with the anticipated low thermal barrier of their interconversion.
authors.affiliation: Department of Chemistry, Marquette University , P.O. Box 1881, Milwaukee, Wisconsin 53233, United States.
authors.forename: Marat R
authors.initials: MR
authors.lastname: Talipov
authors.affiliation: Department of Chemistry, Marquette University , P.O. Box 1881, Milwaukee, Wisconsin 53233, United States.
authors.forename: Maxim V
authors.initials: MV
authors.lastname: Ivanov
authors.affiliation: Department of Chemistry, Marquette University , P.O. Box 1881, Milwaukee, Wisconsin 53233, United States.
authors.forename: Scott A
authors.initials: SA
authors.lastname: Reid
authors.affiliation: Department of Chemistry, Marquette University , P.O. Box 1881, Milwaukee, Wisconsin 53233, United States.
authors.forename: Rajendra
authors.initials: R
authors.lastname: Rathore