title: Effects of (multi)branching of dipolar chromophores on photophysical properties and two-photon absorption.
abstract: To investigate the effect of branching on linear and nonlinear optical properties, a specific series of chromophores, epitome of (multi)branched dipoles, has been thoroughly explored by a combined theoretical and experimental approach. Excited-state structure calculations based on quantum-chemical techniques (time-dependent density functional theory) as well as a Frenkel exciton model nicely complement experimental photoluminescence and one- and two-photon absorption findings and contribute to their interpretation. This allowed us to get a deep insight into the nature of fundamental excited-state dynamics and the nonlinear optical (NLO) response involved. Both experiment and theory reveal that a multidimensional intramolecular charge transfer takes place from the donating moiety to the periphery of the branched molecules upon excitation, while fluorescence stems from an excited state localized on one of the dipolar branches. Branching is also observed to lead to cooperative enhancement of two-photon absorption (TPA) while maintaining high fluorescence quantum yield, thanks to localization of the emitting state. The comparison between results obtained in the Frenkel exciton scheme and ab initio results suggests the coherent coupling between branches as one of the possible mechanisms for the observed enhancement. New strategies for the rational design of NLO molecular assemblies are thus inferred on the basis of the acquired insights.
authors.affiliation: Synthèse et ElectroSynthèse Organiques (CNRS, UMR 6510), Université de Rennes 1, Institut de Chimie, Campus Scientifique de Beaulieu, Bât 10A, F-35042 Rennes Cedex, France.
authors.forename: Claudine
authors.initials: C
authors.lastname: Katan
authors.forename: Francesca
authors.initials: F
authors.lastname: Terenziani
authors.forename: Olivier
authors.initials: O
authors.lastname: Mongin
authors.forename: Martinus H V
authors.initials: MH
authors.lastname: Werts
authors.forename: Laurent
authors.initials: L
authors.lastname: Porrès
authors.forename: Thomas
authors.initials: T
authors.lastname: Pons
authors.forename: Jerome
authors.initials: J
authors.lastname: Mertz
authors.forename: Sergei
authors.initials: S
authors.lastname: Tretiak
authors.forename: Mireille
authors.initials: M
authors.lastname: Blanchard-Desce
mesh_terms: D000042:Absorption; D004396:Coloring Agents / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D010777:Photochemistry; D017785:Photons; D013057:Spectrum Analysis
chemical_list: D004396:Coloring Agents