title: Ultrafast resonance energy transfer in the umbelliferone-alizarin bichromophore.
abstract: In this work we present the synthesis, time-resolved spectroscopic characterization and computational analysis of a bichromophore composed of two very well-known naturally occurring dyes: 7-hydroxycoumarin (umbelliferone) and 1,2-dihydroxyanthraquinone (alizarin). The umbelliferone donor (Dn) and alizarin acceptor (Ac) moieties are linked to a triazole ring viaσ bonds, providing a flexible structure. By measuring the fluorescence quantum yields and the ultrafast transient absorption spectra we demonstrate the high efficiency (∼85%) and the fast nature (∼1.5 ps) of the energy transfer in this compound. Quantum chemical calculations, within the density functional theory (DFT) approach, are used to characterize the electronic structure of the bichromophore (Bi) in the ground and excited states. We simulate the absorption and fluorescence spectra using the TD-DFT methods and the vertical gradient approach (VG), and include the solvent effects by adopting the conductor-like polarizable continuum model (CPCM). The calculated electronic structure suggests the occurrence of weak interactions between the electron densities of Dn and Ac in the excited state, indicating that the Förster-type transfer is the appropriate model for describing the energy transfer in this system. The average distance between Dn and Ac moieties calculated from the conformational analysis (12 Å) is in very good agreement with the value estimated from the Förster equation (∼11 Å). At the same time, the calculated rate constant for energy transfer, averaged over multiple conformations of the system (3.6 ps), is in reasonable agreement with the experimental value (1.6 ps) estimated by transient absorption spectroscopy. The agreement between experimental results and computational data leads us to conclude that the energy transfer in Bi is well described by the Förster mechanism.
authors: LENS (European laboratory for non linear spectroscopy), via N. Carrara 1, 50019 Sesto Fiorentino (FI), Italy.
authors: Andrea
authors: A
authors: Lapini
authors: Pierangelo
authors: P
authors: Fabbrizzi
authors: Matteo
authors: M
authors: Piccardo
authors: Mariangela
authors: M
authors: di Donato
authors: Luisa
authors: L
authors: Lascialfari
authors: Paolo
authors: P
authors: Foggi
authors: Stefano
authors: S
authors: Cicchi
authors: Malgorzata
authors: M
authors: Biczysko
authors: Ivan
authors: I
authors: Carnimeo
authors: Fabrizio
authors: F
authors: Santoro
authors: Chiara
authors: C
authors: Cappelli
authors: Roberto
authors: R
authors: Righini
mesh_terms: D000880:Anthraquinones / Q000737:chemistry*; D004735:Energy Transfer; D013057:Spectrum Analysis / Q000379:methods; D014468:Umbelliferones / Q000737:chemistry*
chemical_list: D000880:Anthraquinones; D014468:Umbelliferones; C010078:alizarin; C031477:7-hydroxycoumarin