Ultrafast resonance energy transfer in the umbelliferone-alizarin bichromophore

Year: 2014

Authors: Lapini A., Fabbrizzi P., Piccardo M., Di Donato M., Lascialfari L., Foggi P., Cicchi S., Biczysko M., Carnimeo I., Santoro F., Cappelli C., Righini R.

Autors Affiliation: LENS (European Laboratory for Non Linear Spectroscopy), via N. Carrara 1, 50019 Sesto Fiorentino (FI), Italy; INO (Istituto Nazionale di Ottica), Largo Fermi 6, 50125 Firenze, Italy; Dipartimento di Chimica ‘Ugo Schiff’, Universitá di Firenze, via della Lastruccia 13, 50019 Sesto Fiorentino (FI), Italy; Dipartimento di Chimica e Chimica Industriale, Università di Pisa, via Risorgimento 35, I-56126 Pisa, Italy; Scuola Normale Superiore, Piazza dei Cavalieri 7, I-56126 Pisa, Italy; Dipartimento di Chimica, Università Degli Studi di Perugia, via Elce di Sotto 8, 06123 Perugia, Italy; CNR-Consiglio Nazionale Delle Ricerche, Istituto di Chimica Dei Composti Organometallici (ICCOM-CNR), UOS di Pisa, Area della Ricerca via G. Moruzzi 1, I-56124 Pisa, Italy

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 via sigma bonds, providing a flexible structure. By measuring the fluorescence quantum yields and the ultrafast transient absorption spectra we demonstrate the high efficiency (similar to 85%) and the fast nature (similar to 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 Forster-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 angstrom) is in very good agreement with the value estimated from the Forster equation (similar to 11 angstrom ). 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 Forster mechanism.


Volume: 16 (21)      Pages from: 10059  to: 10074

More Information: The authors acknowledge the financial support of the Italian MIUR (FIRB ‘Futuro in Ricerca’ 2010, RBFR10Y5VW to M. D.D. and C. C.; FIRB ‘Futuro in Ricerca’ 2010, RBFR109ZHQ to A.L.; PRIN 2010-2011, 2010ERFKXL ”Frontiers studies in molecular spectroscopy and dynamics” to F.S. and R.R.). The financial support of the Cassa di Risparmio di Firenze is also gratefully acknowledged. C.C. and M.B. acknowledge support from COST (Action CODECS: COnvergent Distributed Environment for Computational Spectroscopy). A.L. acknowledges the support of Regione Toscana through PORFSE 2007-2013, project EPHODS.
KeyWords: 7-hydroxycoumarin; alizarin; anthraquinone derivative; umbelliferone derivative, chemistry; energy transfer; procedures; spectroscopy, Anthraquinones; Energy Transfer; Spectrum Analysis; Umbelliferones
DOI: 10.1039/c3cp54609h

Citations: 8
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