title: Biradicaloid character of thiophene-based heterophenoquinones: the role of electron-phonon coupling.
abstract: The quinoidal versus biradicaloid character of the ground state of a series of thiophene-based heterophenoquinones is investigated with quantum-chemical calculations. The role of the ground-state electronic character on molecular structure and vibrational properties is emphasized. The vibrational activities are experimentally determined and their analysis is performed by taking advantage of the definition of a collective vibrational coordinate (the R coordinate) maximizing the electron-phonon coupling, and connecting the quinoid and the aromatic biradicaloid resonance structures. The combined experimental and computational investigation supports the biradicaloid nature of the longer oligomers. The modulation of Raman intensities and frequency dispersion, experimentally observed by increasing the length of the chromophore, is shown to be reproduced well by model calculations on a single chromophore as a function of geometry displacements along the R-mode. These results underline the role of electron-phonon coupling in governing the structure-property relationship of highly conjugated organic compounds, underscoring the similarity of thiophene heterophenoquinone systems with other, more classical, oligophenylene and oligothiophene derivatives.
authors.affiliation: Center for Nano Science and Technology CNST-IIT@PoliMi, Italian Institute of Technology, via Pascoli 70/3, 20133 Milano, Italy. daniele.fazzi@iit.it
authors.forename: Daniele
authors.initials: D
authors.lastname: Fazzi
authors.forename: Eleonora V
authors.initials: EV
authors.lastname: Canesi
authors.forename: Fabrizia
authors.initials: F
authors.lastname: Negri
authors.forename: Chiara
authors.initials: C
authors.lastname: Bertarelli
authors.forename: Chiara
authors.initials: C
authors.lastname: Castiglioni