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Exploration of the π-Electronic Structure of Singlet, Triplet, and Quintet States of Fulvenes and Fulvalenes Using the Electron Localization Function
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
Department of Chemistry, University of Copenhagen.
Department of Chemistry, University of Copenhagen.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
2012 (English)In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 116, no 20, 5008-5017 p.Article in journal (Refereed) Published
Abstract [en]

The singlet ground states and lowest triplet states of penta- and heptafulvene, their benzannulated derivatives, as well as the lowest quintet states of pentaheptafulvalenes, either the parent compound or compounds in which the two rings are intercepted by either an alkynyl or a phenyl segment, were investigated at the (U)OLYP/6-311G(d,p) density functional theory level. The influence of (anti)-aromaticity was analyzed by the structure-based aromaticity index HOMA, the harmonic oscillator model of aromaticity. The extent of (anti)aromatic character was also evaluated in terms of the pi-electron (de)localization as measured by the pi component of the electron localization function (ELF pi). The natural atomic orbital (NAO) occupancies were calculated in order to evaluate the degree of pi-electron shift caused by the opposing electron-counting rules for aromaticity in the electronic ground state (S-0; Hiickel's rule) and the first pi pi* excited triplet state (T-1; Baird's rule). Pentaheptafulvalene (5) shows a shift of 0.5 pi electrons from the 5-ring to the 7-ring when going from the S-0 state to the lowest quintet state (Qu(1)). The pentaheptafulvalene 5 and [5.6.7]quinarene 7 were also investigated in their 90 degrees twisted conformations. From our study it is apparent that excitation localization in fulvalenes, but not in fulvenes, to a substantial degree is determined by aromaticity localization to triplet biradical 4n pi-electron cycles. Isolated benzene rings in these compounds tend to remain as closed-shell 6 pi-electron cycles.

Place, publisher, year, edition, pages
2012. Vol. 116, no 20, 5008-5017 p.
National Category
Organic Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-172377DOI: 10.1021/jp3032397ISI: 000304338600021OAI: oai:DiVA.org:uu-172377DiVA: diva2:514454
Available from: 2012-04-09 Created: 2012-04-09 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Ground and Excited State Aromaticity: Design Tools for π-Conjugated Functional Molecules and Materials
Open this publication in new window or tab >>Ground and Excited State Aromaticity: Design Tools for π-Conjugated Functional Molecules and Materials
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The main focus of this thesis is on the aromaticity of the ground state and electronically excited states of π-conjugated molecules and polymers, as well as how aromaticity is connected to their properties.

The electronic structures of polybenzenoid hydrocarbons (PBHs) were explored through density functional theory (DFT) calculations and the π-component of the electron localization function (ELFπ). The study revealed how the π-electronic structure is influenced by the fusion of double bonds or benzene rings to the PBHs. We also demonstrated that the π-electrons of benzene extend to accommodate as much aromaticity as possible when bond length distorted.  

The aromatic chameleon property displayed by fulvenes, isobenzofulvenes, fulvalenes, bis(fulvene)s, and polyfulvenes were investigated using DFT calculations. The tria-, penta-, and heptafulvenes were shown to possess ionization energies and electron affinities which can be tuned extensively by substitution, some of which even outperform TTF and TCNQ, the prototypical electron donor and acceptor, respectively. The singlet-triplet energy gap of pentafulvenes can be tuned extensively by substitution to the point that the triplet state is lower than the singlet state and thus becomes the ground state. The ELFπ of isobenzofulvene shows that the benzene ring in an electronically excited state can be more aromatic than the corresponding ring in the ground state. We have shown that the 6-ring of [5.6.7]quinarene is influenced by a Hückel aromatic resonance structure with 4n+2 π-electrons in the excited quintet state. The bis(fulvene)s which are composed of a donor type heptafulvene and an acceptor type pentafulvene, retain the basic donor-acceptor properties of the two fragments and could function as compact donor-acceptor dyads. A few of the designed polyfulvenes were found to have band gaps below 1 eV at the PBC-B3LYP/6-31G(d) level.

Various 2,7-disubstituted fluorenones and dibenzofulvenes were synthesized and their excited state properties were investigated by absorption spectroscopy and time-dependent DFT calculations. It was found that the 1A1B transition of ππ* character can be tuned by substitution in the 2,7-positions. The 2,7-bis(N,N-dimethyl) derivatives of fluorenone and dibenzofulvene displayed low energy transitions at 2.18 and 1.61 eV, respectively, in toluene.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. 84 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 929
Keyword
fulvene, fulvalene, polyfulvene, aromaticity, triplet state, excited state, Clar structure, polybenzenoid hydrocarbons (PBH), conjugated polymers, computational chemistry, optical spectroscopy
National Category
Organic Chemistry
Research subject
Chemistry with specialization in Organic Chemistry
Identifiers
urn:nbn:se:uu:diva-173115 (URN)978-91-554-8362-3 (ISBN)
Public defence
2012-06-05, B42, BMC, Husargatan 3, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2012-05-14 Created: 2012-04-18 Last updated: 2012-08-01Bibliographically approved

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Dahlstrand, ChristianOttosson, Henrik

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