title: From linear to cyclic oligoparaphenylenes: electronic and molecular changes traced in the vibrational Raman spectra and reformulation of the bond length alternation pattern.
abstract: Cyclic paraphenylenes, [n]CPPs, and linear paraphenylenes, [n]LPPs, formed by n benzenes, are investigated by Raman spectroscopy for n = 5 to 12 and density functional theory (DFT) for n = 4 to 20. The information on the experimental Raman frequencies and intensities, combined with DFT computations and reported X-ray diffraction structures, provides a consistent interpretation of the Raman spectra and allows establishing relevant structure-property trends. Structural and electronic effects such as benzene ring bending, inter-ring torsions, π-conjugation (aromaticity) and orbital energy gaps as a function of the linear elongation in [n]LPPs versus the macrocyclic curvature in [n]CPPs and of the molecular size (i.e., polymer limit) are systematically analyzed on the basis of the vibrational Raman properties. Changes in the BLA as an indicator of the degree of quinonoid character are analyzed and linked to the Effective Conjugation Coordinate (ECC) model. The BLA patterns involved in twisted and non-twisted conformations and in different species (bipolarons, quinonoid tautomers, and ECC active modes) are compared and their differences are discussed. This paper offers a unified interpretation of structural and electronic aspects in relation to the evolution from linear 1D π-systems to cyclic 2D structures.
authors.affiliation: MALTA-Consolider Team, Department of Physical Chemistry, Chemistry Faculty, University Complutense of Madrid, 28040 Madrid, Spain and Department of Chemistry and Institute of Soft Matter, Georgetown University, 37th and O Streets, NW, Washington, D.C. 20057-1227, USA. Kertesz@georgetown.edu.
authors.forename: Miriam
authors.initials: M
authors.lastname: Peña-Alvarez
authors.affiliation: Department of Chemistry and Institute of Soft Matter, Georgetown University, 37th and O Streets, NW, Washington, D.C. 20057-1227, USA. Kertesz@georgetown.edu.
authors.forename: Lili
authors.initials: L
authors.lastname: Qiu
authors.affiliation: MALTA-Consolider Team, Department of Physical Chemistry, Chemistry Faculty, University Complutense of Madrid, 28040 Madrid, Spain.
authors.forename: Mercedes
authors.initials: M
authors.lastname: Taravillo
authors.affiliation: MALTA-Consolider Team, Department of Physical Chemistry, Chemistry Faculty, University Complutense of Madrid, 28040 Madrid, Spain.
authors.forename: Valentín G
authors.initials: VG
authors.lastname: Baonza
authors.affiliation: Department of Physical Chemistry, University of Málaga, CEI Andalucía Tech, Campus de Teatinos s/n, 29071-Málaga, Spain. casado@uma.es.
authors.forename: M Carmen Ruiz
authors.initials: MC
authors.lastname: Delgado
authors.affiliation: Chemical Research, Kyoto University, Uji 611-0011, Japan.
authors.forename: Shigeru
authors.initials: S
authors.lastname: Yamago
authors.affiliation: Department of Chemistry and Biochemistry and Materials Science Institute 1253, University of Oregon, Eugene, Oregon 97403, USA.
authors.forename: Ramesh
authors.initials: R
authors.lastname: Jasti
authors.affiliation: Department of Physical Chemistry, University of Málaga, CEI Andalucía Tech, Campus de Teatinos s/n, 29071-Málaga, Spain. casado@uma.es.
authors.forename: Juan T López
authors.initials: JT
authors.lastname: Navarrete
authors.affiliation: Department of Physical Chemistry, University of Málaga, CEI Andalucía Tech, Campus de Teatinos s/n, 29071-Málaga, Spain. casado@uma.es.
authors.forename: Juan
authors.initials: J
authors.lastname: Casado
authors.affiliation: Department of Chemistry and Institute of Soft Matter, Georgetown University, 37th and O Streets, NW, Washington, D.C. 20057-1227, USA. Kertesz@georgetown.edu.
authors.forename: Miklos
authors.initials: M
authors.lastname: Kertesz