Transient absorption spectroscopy of a heteroaromatic donor-acceptor-p- conjugated 2,2

Year: 2011

Authors: Mosquera Vázquez S., Abbotto A., De Angelis F., Foggi P., Lapini A., Lobello M., Marcelli A., Tourón Touceda P.

Autors Affiliation: LENS, University of Florence, via Nello Carrara 1, I-50019 Sesto Fiorentino (FI), Italy;
Department Sci. Mat., University of Milano Bicocca, UdR INSTM, via Cozzi 53, I-20125 Milan, Italy;
Istituto CNR di Scienze e Tecnologie Molecolari (CNR-ISTM), via Elce di Sotto 8, I-06100 Perugia, Italy;
Department of Chemistry, University of Perugia, via Elce di Sotto 8, I-06100 Perugia, Italy

Abstract: We report on a study of the excited state dynamics of a heteroaromatic 4,4\’-pi-conjugated 2,2\’-bipyridine dye, bearing conjugated pi-excessive and pi-deficient heteroaromatic rings as donor and acceptor substituents, by means of steady state and transient absorption spectroscopy in EtOH solutions and a room temperature. The ground state absorption shows an intense intramolecular charge transfer band in the visible region with a maximum at 515 nm. Excited state dynamics is measured by pumping at 480 nm at shorter wavelengths from the absorption maximum and probing at specific wavelengths corresponding to bleaching, stimulated emission and at the maximum of excited state absorption. The spectral evolution is also evaluated in the frequency domain as a function of the delay between pump and probe pulses. By means of SVD analysis two components with time constants around 2 ps and 150 ps are identified. In addition a relevant dynamical Stokes shift of the stimulated emission occurs in the first 60 ps which is attributed to solvent dynamics. Ab initio calculations allows to assign the ground spectral features and the excited state conformation. The geometry of the ground and of the first excited state are optimized both in the cisoid and in the transoid forms. The latter results more stable of about 0.4 eV. (c) 2011 Elsevier B.V. All rights reserved.

Journal/Review: JOURNAL OF MOLECULAR STRUCTURE

Volume: 993 (1-3)      Pages from: 464  to: 469

More Information: Istituto Italiano di Tecnologia, IIT. Food and Drug Administration, FDA. Science for Equity, Empowerment and Development Division, SEED. Regione Toscana. – A.L. and A.M. wish to acknowledge the grant financial support by Regione Toscana under the project EPHODS (POR FSE 2007-2013 obiettivo 2 Asse IV). FDA and MGL thank Fondazione Istituto Italiano di Tecnologia, Project SEED 2009 “HELYOS” and MIUR-PRIN for financial support.
KeyWords: Ab initio calculations; Absorption maxima; Bipyridines; Donor and acceptor; Donor-acceptors; Excited state absorption; Excited-state dynamics; First excited state; Frequency domains; Ground state absorption; Intra-molecular charge transfer; Pump-and-probe; Room temperature; Shorter wavelength; Solvent dynamics; Spectral evolution; Spectral feature; Steady state; Stokes shift; Time constants; Transient absorption; Transient absorption spectroscopies; Two-component; Ultrafast spectroscopy; Visible region, Absorption; Calculations; Charge transfer; Dynamics; Energy transfer; Excited states; Ion exchange; Mass transfer; Optical pumping; Stimulated emission, Absorption spectroscopy
DOI: 10.1016/j.molstruc.2011.01.042

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