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Tetrathiafulvalene-based mixed-valence acceptor-donor-acceptor triads: A joint theoretical and experimental approach

AuthorsCalbo, Joaquín; Aragó, Juan; Otón, Francisco ; Lloveras, Vega ; Mas Torrent, Marta ; Vidal Gancedo, José ; Veciana, Jaume ; Rovira, Concepció ; Ortí, Enrique
KeywordsMixed-valent compounds
EPR spectroscopy
Electronic structure
Donor–acceptor systems
Density functional calculations
Issue Date2-Dec-2013
PublisherJohn Wiley & Sons
CitationChemistry - A European Journal 19(49): 16656- 16664 (2013)
AbstractThis work presents a joint theoretical and experimental characterisation of the structural and electronic properties of two tetrathiafulvalene (TTF)-based acceptor-donor-acceptor triads (BQ-TTF-BQ and BTCNQ-TTF - BTCNQ; BQ is naphthoquinone and BTCNQ is benzotetracyano-p-quinodimethane) in their neutral and reduced states. The study is performed with the use of electrochemical, electron paramagnetic resonance (EPR), and UV/Vis/NIR spectroelectrochemical techniques guided by quantum-chemical calculations. Emphasis is placed on the mixed-valence properties of both triads in their radical anion states. The electrochemical and EPR results reveal that both BQ-TTF-BQ and BTCNQ-TTF-BTCNQ triads in their radical anion states behave as class-II mixed-valence compounds with significant electronic communication between the acceptor moieties. Density functional theory calculations (BLYP35/cc-pVTZ), taking into account the solvent effects, predict charge-localised species (BQ.--TTF-BQ and BTCNQ.--TTF-BTCNQ) as the most stable structures for the radical anion states of both triads. A stronger localisation is found both experimentally and theoretically for the BTCNQ-TTF-BTCNQ anion, in accordance with the more electron-withdrawing character of the BTCNQ acceptor. CASSCF/CASPT2 calculations suggest that the low-energy, broad absorption bands observed experimentally for the BQ-TTF-BQ and BTCNQ-TTF-BTCNQ radical anions are associated with the intervalence charge transfer (IV-CT) electronic transition and two nearby donor-to-acceptor CT excitations. The study highlights the molecular efficiency of the electron-donor TTF unit as a molecular wire connecting two acceptor redox centres. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Identifiersdoi: 10.1002/chem.201302910
issn: 0947-6539
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