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Dunlop D, Ludvíková L, Banerjee A, Ottosson H, Slanina T. Excited-State (Anti)Aromaticity Explains Why Azulene Disobeys Kasha's Rule. J Am Chem Soc 2023; 145:21569-21575. [PMID: 37704031 PMCID: PMC10557139 DOI: 10.1021/jacs.3c07625] [Citation(s) in RCA: 12] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2023] [Indexed: 09/15/2023]
Abstract
Fluorescence exclusively occurs from the lowest excited state of a given multiplicity according to Kasha's rule. However, this rule is not obeyed by a handful of anti-Kasha fluorophores whose underlying mechanism is still understood merely on a phenomenological basis. This lack of understanding prevents the rational design and property-tuning of anti-Kasha fluorophores. Here, we propose a model explaining the photophysical properties of an archetypal anti-Kasha fluorophore, azulene, based on its ground- and excited-state (anti)aromaticity. We derived our model from a detailed analysis of the electronic structure of the ground singlet, first excited triplet, and quintet states and of the first and second excited singlet states using the perturbational molecular orbital theory and quantum-chemical aromaticity indices. Our model reveals that the anti-Kasha properties of azulene and its derivatives result from (i) the contrasting (anti)aromaticity of its first and second singlet excited states (S1 and S2, respectively) and (ii) an easily accessible antiaromaticity relief pathway of the S1 state. This explanation of the fundamental cause of anti-Kasha behavior may pave the way for new classes of anti-Kasha fluorophores and materials with long-lived, high-energy excited states.
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Affiliation(s)
- David Dunlop
- Institute
of Organic Chemistry and Biochemistry of the Czech Academy of Sciences, Flemingovo náměstí
542/2, Prague 6 160 00, Czech Republic
- Department
of Inorganic Chemistry, Faculty of Science, Charles University in Prague, Hlavova 2030, Prague 2 128 40, Czech Republic
| | - Lucie Ludvíková
- Institute
of Organic Chemistry and Biochemistry of the Czech Academy of Sciences, Flemingovo náměstí
542/2, Prague 6 160 00, Czech Republic
| | - Ambar Banerjee
- Division
of X-ray Photon Science, Department of Physics and Astronomy—Ångström
Laboratory, Uppsala University, Box 523, Uppsala 751 20, Sweden
| | - Henrik Ottosson
- Department
of Chemistry—Ångström Laboratory, Uppsala University, Box 516, Uppsala 751 20, Sweden
| | - Tomáš Slanina
- Institute
of Organic Chemistry and Biochemistry of the Czech Academy of Sciences, Flemingovo náměstí
542/2, Prague 6 160 00, Czech Republic
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2
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Oruganti B, Wang J, Durbeej B. Modulating the Photocyclization Reactivity of Diarylethenes through Changes in the Excited-State Aromaticity of the π-Linker. J Org Chem 2022; 87:11565-11571. [PMID: 35997595 PMCID: PMC9442643 DOI: 10.1021/acs.joc.2c01172] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Quantum chemical calculations are performed to explore if the reactivity of diarylethene switches toward photocyclization can be controlled by the excited-state aromaticity of their bridging π-linker. Using an archetypal diarylethene with a non-aromatic π-linker as a reference, completely different outcomes are found when the π-linker is allowed to become either aromatic (no reaction) or antiaromatic (fast reaction) upon photoexcitation. The results demonstrate a possibility to use the excited-state aromaticity concept for actual modulation of photochemical reactivity.
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Affiliation(s)
- Baswanth Oruganti
- Division of Theoretical Chemistry, IFM, Linköping University, Linköping SE-58183, Sweden.,Department of Chemistry, SRM University-AP, Mangalagiri, Andhra Pradesh 522240, India
| | - Jun Wang
- Jiangsu Key Laboratory for Chemistry of Low-Dimensional Materials, Jiangsu Engineering Laboratory for Environment Functional Materials, School of Chemistry and Chemical Engineering, Huaiyin Normal University, Huaian 223300, China
| | - Bo Durbeej
- Division of Theoretical Chemistry, IFM, Linköping University, Linköping SE-58183, Sweden
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3
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Karas LJ, Wu CH, Wu JI. Barrier-Lowering Effects of Baird Antiaromaticity in Photoinduced Proton-Coupled Electron Transfer (PCET) Reactions. J Am Chem Soc 2021; 143:17970-17974. [PMID: 34672631 DOI: 10.1021/jacs.1c09324] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Many popular organic chromophores that catalyze photoinduced proton-coupled electron transfer (PCET) reactions are aromatic in the ground state but become excited-state antiaromatic in the lowest ππ* state. We show that excited-state antiaromaticity makes electron transfer easier. Two representative photoinduced electron transfer processes are investigated: (1) the photolysis of phenol and (2) solar water splitting of a pyridine-water complex. In the selected reactions, the directions of electron transfer are opposite, but the net result is proton transfer following the direction of electron transfer. Nucleus-independent chemical shifts (NICS), ionization energies, electron affinities, and PCET energy profiles of selected [4n] and [4n + 2] π-systems are presented, and important mechanistic implications are discussed.
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Affiliation(s)
- Lucas J Karas
- Department of Chemistry, University of Houston, Houston, Texas 77204, United States
| | - Chia-Hua Wu
- Department of Chemistry, University of Houston, Houston, Texas 77204, United States
| | - Judy I Wu
- Department of Chemistry, University of Houston, Houston, Texas 77204, United States
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4
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Ganguly G, Pathak S, Paul A. Unraveling the stability of cyclobutadiene complexes using aromaticity markers. Phys Chem Chem Phys 2021; 23:16005-16012. [PMID: 34235525 DOI: 10.1039/d1cp01467f] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Cyclobutadiene (CBD) is the paradigmatic antiaromatic molecule but is known to form highly stable aromatic complexes, e.g. CBD-Fe(CO)3. This intriguing reversal of aromaticity from antiaromatic to aromatic terrain during the complexation process cannot be appropriately handled with single-reference-based theoretical techniques. We explore this aromaticity reversal, for the first time, by a detailed aromaticity analysis using magnetically induced current densities (MICD) and nucleus independent chemical shifts (NICS) using genuine ab initio multi-reference wavefunction-based theory. We trace the dramatic change of aromaticity for a prototypical cyclobutadiene complex, CBD-CH+ (CH+Fe(CO)3), considering a 3D potential energy surface for two independent parameters, namely the approach of CH+ and the automerization cross-section of cyclobutadiene. The 3D potential energy surfaces indicate the presence of a conical intersection/avoided crossing between the ground and the first excited state. The plot of aromaticity indices and the corresponding numerical values show that the change of aromaticity indices is drastic around the conical intersection/avoided crossing and automerization of cyclobutadiene plays a crucial role in the formation of cyclobutadiene complexes. Computations on analogous CBD-Be and CBD-CO systems (Be/COFe(CO)3) emphasize the generality of the conclusions drawn from the CBD-CH+ system.
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Affiliation(s)
- Gaurab Ganguly
- School of Chemical Sciences, Indian Association for the Cultivation of Science, 2A & 2B Raja S C Mullick Road, Kolkata 700032, India.
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5
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Luxford TFM, Fedor J, Kočišek J. Electron attachment to tetrazoles: The influence of molecular structure on ring opening reactivity. J Chem Phys 2021; 154:214303. [PMID: 34240967 DOI: 10.1063/5.0052011] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The electron-induced reactivity of 5-(4-chlorophenyl)-1H-tetrazole and 5-chloro-1-phenyl-1H-tetrazole was studied using a trochoidal electron monochromator quadrupole mass spectrometer experimental setup. 5-(4-chlorophenyl)-1H-tetrazole underwent dissociative electron attachment to form Cl-, [M-HCl]-, and [M-H]-. 5-chloro-1-phenyl-1H-tetrazole underwent associative electron attachment to form the parent anion and dissociative electron attachment to form Cl-, CN2Cl-, [M-N2-Cl]-, and [M-HCl]-. For each anion product, the ion yield was measured as a function of incident electron energy. Density functional theory calculations were performed to support the experimental results with estimates of the energetic thresholds for the different reaction pathways. While the tetrazole group is susceptible to electron-induced ring opening in both molecules, this process was only observed for 5-chloro-1-phenyl-1H-tetrazole, indicating that this process is influenced by the structure of the molecule.
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Affiliation(s)
- T F M Luxford
- J. Heyrovský Institute of Physical Chemistry of the Czech Academy of Sciences, Dolejškova 2155/3, 182 23 Prague 8, Czech Republic
| | - J Fedor
- J. Heyrovský Institute of Physical Chemistry of the Czech Academy of Sciences, Dolejškova 2155/3, 182 23 Prague 8, Czech Republic
| | - J Kočišek
- J. Heyrovský Institute of Physical Chemistry of the Czech Academy of Sciences, Dolejškova 2155/3, 182 23 Prague 8, Czech Republic
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6
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Oruganti B, Pál Kalapos P, Bhargav V, London G, Durbeej B. Photoinduced Changes in Aromaticity Facilitate Electrocyclization of Dithienylbenzene Switches. J Am Chem Soc 2020; 142:13941-13953. [PMID: 32666793 PMCID: PMC7458422 DOI: 10.1021/jacs.0c06327] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
![]()
The concepts of excited-state
aromaticity and antiaromaticity have
in recent years with increasing frequency been invoked to rationalize
the photochemistry of cyclic conjugated organic compounds, with the
long-term goal of using these concepts to improve the reactivities
of such compounds toward different photochemical transformations.
In this regard, it is of particular interest to assess how the presence
of a benzene motif affects photochemical reactivity, as benzene is
well-known to completely change its aromatic character in its lowest
excited states. Here, we investigate how a benzene motif influences
the photoinduced electrocyclization of dithienylethenes, a major class
of molecular switches. Specifically, we report on the synthesis of
a dithienylbenzene switch where the typical nonaromatic, ethene-like
motif bridging the two thienyl units is replaced by a benzene motif,
and show that this compound undergoes electrocyclization upon irradiation
with UV-light. Furthermore, through a detailed quantum chemical analysis,
we demonstrate that the electrocyclization is driven jointly and synergistically
by the loss of aromaticity in this motif from the formation of a reactive,
antiaromatic excited state during the initial photoexcitation, and
by the subsequent relief of this antiaromaticity as the reaction progresses
from the Franck–Condon region. Overall, we conclude that photoinduced
changes in aromaticity facilitate the electrocyclization of dithienylbenzene
switches.
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Affiliation(s)
- Baswanth Oruganti
- Department of Chemistry and Biomedical Sciences, Faculty of Health and Life Sciences, Linnaeus University, SE-45041 Kalmar, Sweden
| | - Péter Pál Kalapos
- MTA-TTK "Lendület" Functional Organic Materials Research Group, Institute of Organic Chemistry, Research Centre for Natural Sciences, 1117 Budapest, Hungary
| | - Varada Bhargav
- Department of Chemistry, GITAM Institute of Science, GITAM (deemed to be University), Visakhapatnam 530045, Andhra Pradesh, India
| | - Gábor London
- MTA-TTK "Lendület" Functional Organic Materials Research Group, Institute of Organic Chemistry, Research Centre for Natural Sciences, 1117 Budapest, Hungary
| | - Bo Durbeej
- Division of Theoretical Chemistry, IFM, Linköping University, SE-58183 Linköping, Sweden
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7
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Halder D, Paul A. Understanding the Role of Aromaticity and Conformational Changes in Bond Dissociation Processes of Photo-Protecting Groups. J Phys Chem A 2020; 124:3976-3983. [PMID: 32338513 DOI: 10.1021/acs.jpca.9b11731] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Photoremovable protecting groups (PPGs) provide spatial and temporal control over the release of various chemicals. Using surface hopping studies with multireference electronic structure methods we have unravelled the nuclear and the electronic events at play. Furthermore, the electronic changes along the reaction path were probed using excited state aromaticity quantifiers and orbital analysis. We find that upon irradiation with light of appropriate wavelength on the substituted coumarin system a π-π* electronic excitation occurs which is followed by an electron loss from the aromatic ring on gaining proper alignment between the π* and the C-LG (LG = leaving group) σ*. This alignment is brought about by a critical dihedral angle change in the molecule, which subsequently triggers C-LG bond cleavage. The sequence of events is indicative of an intramolecular electron catalyzed process which is established through investigations of changes in aromaticity of the phenyl ring which acts as an electron reservoir.
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Affiliation(s)
- Debabrata Halder
- School of Chemical Sciences, Indian Association for the Cultivation of Science, 2A & 2B Raja S C Mullick Road, Kolkata 700032, India
| | - Ankan Paul
- School of Chemical Sciences, Indian Association for the Cultivation of Science, 2A & 2B Raja S C Mullick Road, Kolkata 700032, India
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Mai S, Marquetand P, González L. Nonadiabatic dynamics: The SHARC approach. WILEY INTERDISCIPLINARY REVIEWS. COMPUTATIONAL MOLECULAR SCIENCE 2018; 8:e1370. [PMID: 30450129 PMCID: PMC6220962 DOI: 10.1002/wcms.1370] [Citation(s) in RCA: 224] [Impact Index Per Article: 37.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/14/2018] [Revised: 04/05/2018] [Accepted: 04/06/2018] [Indexed: 12/12/2022]
Abstract
We review the Surface Hopping including ARbitrary Couplings (SHARC) approach for excited-state nonadiabatic dynamics simulations. As a generalization of the popular surface hopping method, SHARC allows simulating the full-dimensional dynamics of molecules including any type of coupling terms beyond nonadiabatic couplings. Examples of these arbitrary couplings include spin-orbit couplings or dipole moment-laser field couplings, such that SHARC can describe ultrafast internal conversion, intersystem crossing, and radiative processes. The key step of the SHARC approach consists of a diagonalization of the Hamiltonian including these couplings, such that the nuclear dynamics is carried out on potential energy surfaces including the effects of the couplings-this is critical in any applications considering, for example, transition metal complexes or strong laser fields. We also give an overview over the new SHARC2.0 dynamics software package, released under the GNU General Public License, which implements the SHARC approach and several analysis tools. The review closes with a brief survey of applications where SHARC was employed to study the nonadiabatic dynamics of a wide range of molecular systems. This article is categorized under: Theoretical and Physical Chemistry > Reaction Dynamics and KineticsSoftware > Simulation MethodsSoftware > Quantum Chemistry.
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Affiliation(s)
- Sebastian Mai
- Institute of Theoretical Chemistry, Faculty of Chemistry University of Vienna Vienna Austria
| | - Philipp Marquetand
- Institute of Theoretical Chemistry, Faculty of Chemistry University of Vienna Vienna Austria
| | - Leticia González
- Institute of Theoretical Chemistry, Faculty of Chemistry University of Vienna Vienna Austria
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Sommerfeld T, Davis MC. Ring-opening attachment as an explanation for the long lifetime of the octafluorooxolane anion. J Chem Phys 2018; 149:084305. [DOI: 10.1063/1.5045088] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Thomas Sommerfeld
- Department of Chemistry and Physics, Southeastern Louisiana University, SLU 10878, Hammond, Louisiana 70402, USA
| | - Megan C. Davis
- Department of Chemistry and Physics, Southeastern Louisiana University, SLU 10878, Hammond, Louisiana 70402, USA
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