Ground and Excited State Aromaticity

86 Pages·2012·4.92 MB·English

by  Christian Dahlstrand

List of Papers
This thesis is based on the following papers, which are referred to in the text
by their Roman numerals.

I Zhu, J.; Dahlstrand, C.; Smith, J. R.; Villaume, S.; Ottosson, H.
On the Importance of Clar Structures of Polybenzenoid
Hydrocarbons as Revealed by the π-contribution to the
Electron Localization Function. Symmetry 2010, 2, 1653-
1682.

II Dahlstrand, C.; Yamazaki, K.; Zhu, J.; Villaume, S.; Kilså, K.;
Ottosson, H. Substituent Effects on the Electron Affinities
and Ionization Energies of Tria-, Penta-, and Heptafulve-
nes: A Computational Study. J. Org. Chem. 2010, 75(23),
8060-8068.

III Tong, H.; Dahlstrand, C.; Villaume, S.; Zhu, J.; Piqueras, M.
C.; Crespo, R.; Ottosson, H. Fulvenes: Compounds for which
the Singlet-Triplet Energy Gaps are Closely Linked to
Aromaticity and Aromaticity Differences. Manuscript (2012)

IV Dahlstrand, C.; Rosenberg, M.; Kilså, K.; Ottosson. H. Explo-
ration of the π-Electronic Structure of Singlet, Triplet, and
Quintet States of Fulvenes, and Fulvalenes Using the Elec-
tron Localization Function. J. Phys. Chem. Accepted (2012)

V Rosenberg, M.; Dahlstrand, C.; Ottosson, H.; Kilså, K. Ma-
nipulation of Excited State Energies in Fulvenic Molecules.
Preliminary manuscript (2012)

VI Dahlstrand, C.; Jahn, B.; Grigoriev, A.; Villaume, S.; Ahuja, R.,
Ottosson, H. Tuning the Band Gap of Polyfulvenes by Use of
“Handles”: On the Effects of Exocyclic Substitution, Ben-
zannulation, and Ring Methylation. Manuscript (2012)
Reprints were made with permission from the respective publishers.
Works not included in this thesis:

• Rosenberg, M.; Dahlstrand, C.; Kilså, K.; Ottosson, H. Excited
State Aromaticity and Antiaromaticity: Opportunities for Photo-
physical and Photochemical Rationalizations. Chem. Rev. Manu-
script (2012)

• Dahlstrand, C. Aromaticity Effects in Polybenzenoid Hydrocar-
bons and in Substituted Fulvenes: A Computational Study. Thesis
for the degree of Licentiate of technology (2010)
Author Contribution
The author wishes to clarify his contributions to the included papers.

I Performed a large part of the calculations and contributed partly
to manuscript writing.

II Performed a large part of the calculations and contributed ex-
tensively to project development, data analysis and manuscript
writing.

III Performed a majority of the calculations, and contributed exten-
sively to data analysis and manuscript writing.

IV Performed a majority of the calculations. Contributed exten-
sively to project development, manuscript writing and data
analysis.

V Preformed all synthetic work and provided the initial computa-
tional results.

VI Performed all oligomer calculations and a few initial PBC cal-
culations. Contributed extensively to project development,
manuscript writing, and data analysis.

Contents
1. Introduction...............................................................................................13
1.1. Single Molecule Electronics..............................................................13
1.2. Electronics based on Molecular Materials........................................14
2. Aromaticity...............................................................................................15
2.1. A Short Historical Background.........................................................15
2.2. Different Types of Aromaticity.........................................................16
2.3. Spin State Multiplicity......................................................................17
2.4. Aromaticity in the Singlet Ground State...........................................18
2.4.1. Aromaticity Criteria...................................................................18
2.5. Aromaticity in the Lowest Triplet and Quintet Excited States..........19
2.6. Aromaticity Indices...........................................................................19
2.6.1. Harmonic Oscillator Model of Aromaticity (HOMA)...............19
2.6.2. Nucleus Independent Chemical Shifts (NICS)..........................20
2.6.3. NICS scan..................................................................................20
2.6.4. Electron Localization Function (ELF).......................................21
3. Computational Quantum Chemistry.........................................................22
3.1. Elementary Quantum Mechanics......................................................22
3.2. Hartree-Fock (HF) and post-Hartree-Fock Methods.........................23
3.3. Basis Sets...........................................................................................24
3.4. Density Functional Theory (DFT).....................................................24
3.5. Calculating Molecular Properties......................................................26
4. Aromaticity of Polybenzenoid Hydrocarbons...........................................27
4.1. Properties of Polybenzenoid Hydrocarbons......................................27
4.1.2. Clar Resonance Structures.........................................................27
4.1.3. Properties of the Electron Localization Function......................29
4.1.4. Describing PBHs through the π-Component of the Electron
Localization Function..........................................................................31
4.2. Influence on π-Electronic Structure due to the Fusion of Ethylene or
Benzene Ring Fragments onto PBHs.......................................................33
4.2.1. Fusion of Ethylene onto a PBH.................................................33
4.2.2. Fusion of a Benzene ring onto a PBH........................................33
4.3. Influence on the π-Electronic Structure of Benzene due to Distortions
of the σ-Framework.................................................................................35
5. Aromatic Chameleons...............................................................................37
5.1. Electron Affinity and Ionization Energy...........................................37
5.1.1. Tetrathiafulvalene and tetracyanoquinodimethane....................38
5.1.2. Basis Set Dependence of the Outer Valence Greens’ Function
Calculations.........................................................................................39
5.1.3. Orbital Symmetry Considerations.............................................40
5.2. Donor-Acceptor Dyads......................................................................43
5.3. Excited States of Pentafulvenes........................................................45
5.3.1. Rotation about the Exocyclic Bond of Substituted Pentafulvene.46
5.3.2. The Gauge Including Atomic Orbitals Method for Nuclear
Magnetic Shieldings............................................................................47
5.3.3. The Connection Between Aromaticity and the Singlet-Triplet
Energy Gap..........................................................................................47
5.3.4. NICS-scan on a Potential Ground State Triplet.........................49
5.3.5. Dependence of HOMA, NICS, and ΔE on the C-C Bond
ST
Lengths................................................................................................50
5.4. π-Electronic Structure of Other Fulvenoid Compounds...................54
5.4.1. Fulvenes and Fulvalenes Investigated by the π-Component of
the Electron Localization Function......................................................54
6. Excited State Properties of Substituted Fluorenones and Dibenzofulvenes58
6.1. Synthetic Aspects..............................................................................58
6.2. Excited State Properties of Substituted Fluorenones and
Dibenzofulvenes.......................................................................................60
6.2.2. Time-Dependent Density Functional Theory............................60
6.2.3. Polarizable Continuum Model (PCM).......................................61
6.2.4. Exchange of O for C(CN) .........................................................61
2
6.2.5. Substitution at the 2- and 7- positions.......................................62
7. Fulvenes in Polymeric Systems................................................................66
7.1. Conducting Polymers........................................................................66
7.2. Oligomer Extrapolations...................................................................67
7.3. Periodic Boundary Conditions (PBC)...............................................69
7.3.1. Fulvenoid or Quinoid Polyfulvenes...........................................69
7.3.2. Effect of Benzannulation...........................................................70
7.3.3. Benzannulation and Aromaticity...............................................72
8. Concluding Remarks.................................................................................73
9. Summary in Swedish................................................................................74
9.1. Aromaticitet.......................................................................................74
9.2. Polybensenoida kolväten...................................................................75
9.3. Aromatiska kameleonter....................................................................75
9.4. Ledande polymerer............................................................................77
9.5. Slutsats..............................................................................................78
Acknowledgements.......................................................................................79
References.....................................................................................................81
Abbreviations
ΔE Singlet-Triplet Energy Gap
ST
ΔBV Bifurcation Value Difference
ΑΝΟ Atomic Natural Orbital
AO Atomic Orbital
BLA Bond Length Alternation
BV Bifurcation Value
CASSCF Complete Active Space Self-Consistent Field
CASPT2 CASSCF with Second-Order Perturbation Theory
CGTF Contracted Gaussian Type Function
DCM Dichloromethane
DFT Density Functional Theory
DMSO Dimethylsulfoxide
E Band Gap Energy
g
E Fermi Energy
F
EA Electron Affinity
EDG Electron Donating Group
ELF Electron Localization Function
ELF π-Component of Electron Localization Function
π
eV Electron Volt
EWG Electron Withdrawing Group
f Fulvenoid-type Structure
FET Field-Effect Transistor
GGA Generalized Gradient Approximation
GIAO Gauge Including Atomic Orbital
GTF Gaussian Type Function
HF Hartree-Fock
HOCO Highest Occupied Crystal Orbital
HOMA Harmonic Oscillator Measure of Aromaticity
HOMO Highest Occupied Molecular Orbital
HOPG Highly Oriented Pyrolytic Graphite