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Salikov RF, Belyy AY, Ilyushchenko MK, Platonov DN, Sokolova AD, Tomilov YV. Antiaromaticity of Cycloheptatrienyl Anions: Structure, Acidity, and Magnetic Properties. Chemistry 2024; 30:e202401041. [PMID: 38785416 DOI: 10.1002/chem.202401041] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2024] [Revised: 05/23/2024] [Accepted: 05/24/2024] [Indexed: 05/25/2024]
Abstract
Investigations of the nature and degree of antiaromaticity of cycloheptatrienyl anion derivatives using both experimental and computational tools are presented. The ground state of cycloheptatrienyl anion in the gas phase is triplet, planar and Baird-aromatic. In DMSO, it assumes a singlet distorted allylic form with a paratropic ring current. The other derivatives in both phases assume either allylic or diallylic conformations depending on the substituent pattern. A combination of experimental and computational methods was used to determine the pKa values of 16 derivatives in DMSO, which ranged from 36 to -10.7. We revealed that the stronger stabilization of the anionic system, which correlates with acidity, does not necessarily imply a lower degree of antiaromaticity in terms of magnetic properties. Conversely, the substitution pattern first affects the geometry of the ring through the bulkiness of the substituents and their better conjugation with a more distorted system. Consequently, the distortion reduces the cyclic conjugation in the π-system and thereby decreases the paratropic current in a magnetic field, which manifests itself as a decrease in the NICS. The triplet-state geometries and magnetic properties are nearly independent on the substitution pattern, which is typical for simple aromatic systems.
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Affiliation(s)
- Rinat F Salikov
- N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 47 Leninsky prosp., Moscow, 119991, Russian Federation
- Department of Chemistry, Higher School of Economics National Research University, Moscow, 101000, Russian Federation
| | - Alexander Y Belyy
- N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 47 Leninsky prosp., Moscow, 119991, Russian Federation
| | - Matvey K Ilyushchenko
- N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 47 Leninsky prosp., Moscow, 119991, Russian Federation
| | - Dmitry N Platonov
- N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 47 Leninsky prosp., Moscow, 119991, Russian Federation
| | - Alena D Sokolova
- N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 47 Leninsky prosp., Moscow, 119991, Russian Federation
| | - Yury V Tomilov
- N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 47 Leninsky prosp., Moscow, 119991, Russian Federation
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2
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Leyva-Parra L, Casademont-Reig I, Pino-Rios R, Ruiz L, Alonso M, Tiznado W. New Perspectives on Delocalization Pathways in Aromatic Molecular Chameleons. Chemphyschem 2024; 25:e202400271. [PMID: 38530286 DOI: 10.1002/cphc.202400271] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2024] [Accepted: 03/25/2024] [Indexed: 03/27/2024]
Abstract
This study comprehensively analyzes the magnetically induced current density of polycyclic compounds labeled as "aromatic chameleons" since they can arrange their π-electrons to exhibit aromaticity in both the ground and the lowest triplet state. These compounds comprise benzenoid moieties fused to a central skeleton with 4n π-electrons and traditional magnetic descriptors are biased due to the superposition of local magnetic responses. In the S0 state, our analysis reveals that the molecular constituent fragments preserve their (anti)aromatic features in agreement with two types of resonant structures: one associated with aromatic benzenoids and the other with a central antiaromatic ring. Regarding the T1 state, a global and diatropic ring current is revealed. Our aromaticity study is complemented with advanced electronic and geometric descriptors to consider different aspects of aromaticity, particularly important in the evaluation of excited state aromaticity. Remarkably, these descriptors consistently align with the general features on the main delocalization pathways in polycyclic hydrocarbons consisting of fused 4n π-electron rings. Moreover, our study demonstrates an inverse correlation between the singlet-triplet energy difference and the antiaromatic character of the central ring in S0.
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Affiliation(s)
- Luis Leyva-Parra
- Facultad de Ingeniería y Arquitectura, Universidad Central de Chile (UCEN), Santa Isabel 1186, 8370146, Santiago, Chile
- Centro de Química Teórica & Computacional (CQT&C), Departamento de Ciencias Químicas, Facultad de Ciencias Exactas, Universidad Andres Bello, Av. República 275, 8370146, Santiago, Chile
| | - Irene Casademont-Reig
- Department of General Chemistry (ALGC), Vrije Universiteit Brussel (VUB), Pleinlaan 2, 1050, Brussels, Belgium
| | - Ricardo Pino-Rios
- Centro de Investigación Medicina de Altura, Universidad Arturo Prat, Iquique, 1100000, Chile
- Química y Farmacia, Facultad de Ciencias de la Salud, Universidad Arturo Prat, Casilla 121, Iquique, 1100000, Chile
| | - Lina Ruiz
- Instituto de Ciencias Biomédicas, Facultad de Ciencias de la Salud, Universidad Autónoma de Chile, Santiago, 8910060, Chile
| | - Mercedes Alonso
- Department of General Chemistry (ALGC), Vrije Universiteit Brussel (VUB), Pleinlaan 2, 1050, Brussels, Belgium
| | - William Tiznado
- Centro de Química Teórica & Computacional (CQT&C), Departamento de Ciencias Químicas, Facultad de Ciencias Exactas, Universidad Andres Bello, Av. República 275, 8370146, Santiago, Chile
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3
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Proos Vedin N, Escayola S, Radenković S, Solà M, Ottosson H. The n,π* States of Heteroaromatics: When are They the Lowest Excited States and in What Way Can They Be Aromatic or Antiaromatic? J Phys Chem A 2024; 128:4493-4506. [PMID: 38787346 PMCID: PMC11163469 DOI: 10.1021/acs.jpca.4c02580] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2024] [Revised: 05/10/2024] [Accepted: 05/10/2024] [Indexed: 05/25/2024]
Abstract
Heteroaromatic molecules are found in areas ranging from biochemistry to photovoltaics. We analyze the n,π* excited states of 6π-electron heteroaromatics with in-plane lone pairs (nσ, herein n) and use qualitative theory and quantum chemical computations, starting at Mandado's 2n + 1 rule for aromaticity of separate spins. After excitation of an electron from n to π*, a (4n + 2)π-electron species has 2n + 2 πα-electrons and 2n + 1 πβ-electrons (or vice versa) and becomes πα-antiaromatic and πβ-aromatic. Yet, the antiaromatic πα- and aromatic πβ-components seldom cancel, leading to residuals with aromatic or antiaromatic character. We explore vertically excited triplet n,π* states (3n,π*), which are most readily analyzed, but also singlet n,π* states (1n,π*), and explain which compounds have n,π* states with aromatic residuals as their lowest excited states (e.g., pyrazine and the phenyl anion). If the πβ-electron population becomes more (less) uniformly distributed upon excitation, the system will have an (anti)aromatic residual. Among isomers, the one that has the most aromatic residual in 3n,π* is often of the lowest energy in this state. Five-membered ring heteroaromatics with one or two N, O, and/or S atoms never have n,π* states as their first excited states (T1 and S1), while this is nearly always the case for six-membered ring heteroaromatics with electropositive heteroatoms and/or highly symmetric (D2h) diheteroaromatics. For the complete compound set, there is a modest correlation between the (anti)aromatic character of the n,π* state and the energy gap between the lowest n,π* and π,π* states (R2 = 0.42), while it is stronger for monosubstituted pyrazines (R2 = 0.84).
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Affiliation(s)
- Nathalie Proos Vedin
- Department
of Chemistry—Ångström Laboratory, Uppsala University, 751 20 Uppsala, Sweden
| | - Sílvia Escayola
- Institut
de Quìmica Computacional i Catàlisi and Departament
de Química, Universitat de Girona, C/Maria Aurèlia Capmany,
69, 17003 Girona, Catalonia, Spain
- Donostia
International Physics Center (DIPC), 20018 Donostia, Euskadi, Spain
| | - Slavko Radenković
- Faculty
of Science, University of Kragujevac, P.O. Box 60, 34000 Kragujevac, Serbia
| | - Miquel Solà
- Institut
de Quìmica Computacional i Catàlisi and Departament
de Química, Universitat de Girona, C/Maria Aurèlia Capmany,
69, 17003 Girona, Catalonia, Spain
| | - Henrik Ottosson
- Department
of Chemistry—Ångström Laboratory, Uppsala University, 751 20 Uppsala, Sweden
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Betkhoshvili S, Moreira IDR, Poater J, Maria Bofill J. Pathway to Polyradicals: A Planar and Fully π-Conjugated Organic Tetraradical(oid). J Phys Chem Lett 2024; 15:5243-5249. [PMID: 38718211 PMCID: PMC11103692 DOI: 10.1021/acs.jpclett.4c00686] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2024] [Revised: 04/24/2024] [Accepted: 05/02/2024] [Indexed: 05/22/2024]
Abstract
In this work, we provide a general strategy to stabilize the ground state of polyradical(oid)s and make higher spin states thermally accessible. As a proof of concept, we propose to merge two planar fully π-conjugated diradical(oid)s to obtain a planar and cross-conjugated tetraradical(oid). Using multireference quantum chemistry methods, we show that the designed tetraradical(oid) is stabilized by aromaticity and delozalization in the π-system and has six thermally accessible spin states within 1.72 kcal/mol. Analysis of the electronic structure of these six states of the tetraradical(oid) shows that its frontier π-system consists of two weakly interacting subsystems: aromatic cycles and four unpaired electrons. Conjugation between unpaired electrons, which favors closed-shell structures, is mitigated by delocalization and the aromaticity of the bridging groups, leading to the synergistic cross-coupling between two diradical(oid) subunits to stabilize the tetraradical(oid) electronic structure.
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Affiliation(s)
- Sergi Betkhoshvili
- Departament
de Química Inorgànica i Orgànica and IQTCUB, Universitat de Barcelona, Martí i Franquès 1-11, 08028 Barcelona, Spain
| | - Ibério de
P. R. Moreira
- Departament
de Ciència de Materials i Química Física, Secció
de Qumíca, Física and IQTCUB, Universitat de Barcelona, Martí i Franquès 1-11, 08028 Barcelona, Spain
| | - Jordi Poater
- Departament
de Química Inorgànica i Orgànica and IQTCUB, Universitat de Barcelona, Martí i Franquès 1-11, 08028 Barcelona, Spain
- ICREA, Pg. Lluís Companys 23, 08010 Barcelona, Spain
| | - Josep Maria Bofill
- Departament
de Química Inorgànica i Orgànica and IQTCUB, Universitat de Barcelona, Martí i Franquès 1-11, 08028 Barcelona, Spain
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Cummings E, Karadakov PB. Aromaticity in the Electronic Ground and Lowest Triplet States of Molecules with Fused Thiophene Rings. Chemistry 2024; 30:e202303724. [PMID: 38038597 DOI: 10.1002/chem.202303724] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2023] [Revised: 11/30/2023] [Accepted: 12/01/2023] [Indexed: 12/02/2023]
Abstract
Analysis of the variations of the off-nucleus isotropic magnetic shielding, σiso(r), around thiophene, thienothiophenes, dithienothiophenes and sulflowers in their electronic ground (S0) and lowest triplet (T1) states reveals that some of the features of aromaticity and bonding in these molecules do not fit in with predictions based on the popular Hückel's and Baird's rules. Despite having 4n π electrons, the S0 states of the sulflowers are shown to be aromatic, due to the local aromaticities of the individual thiophene rings. To reduce its T1 antiaromaticity, the geometry of thiophene changes considerably between S0 and T1: In addition to losing planarity, the carbon-carbon two 'double' and one 'single' bonds in S0 turn into two 'single' and one 'double' bonds in T1. Well-defined Baird-style aromaticity reversals are observed between the S0 and T1 states of only three of the twelve thiophene-based compounds investigated in this work, in contrast, the sulflower with six thiophene rings which is weakly aromatic in S0 becomes more aromatic in T1. The results suggest that the change in aromaticity between the S0 and T1 states in longer chains of fused rings is likely to affect mostly the central ring (or the pair of central rings); rings sufficiently far away from the central ring(s) can retain aromatic character.
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Affiliation(s)
- Edward Cummings
- Department of Chemistry, University of York, Heslington, York, YO10 5DD, UK
| | - Peter B Karadakov
- Department of Chemistry, University of York, Heslington, York, YO10 5DD, UK
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Yang G, Yun YJ, Peccati F, Jamhawi AM, Kamatham N, Jockusch S, Jiménez-Osés G, Ayitou AJL. Unraveling the Photophysical Characteristics, Aromaticity, and Stability of π-Extended Acene-Quinodimethyl Thioamides†. Chemphyschem 2023; 24:e202200906. [PMID: 37545345 DOI: 10.1002/cphc.202200906] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2022] [Revised: 07/31/2023] [Accepted: 08/02/2023] [Indexed: 08/08/2023]
Abstract
Poly-aromatic systems that contain quinodimethyl (QDM) units are appealing for several photonic and spintronic applications owing to the unique electronic structure, aromaticity, and spin state(s) of the QDM ring. Herein, we report the synthesis and characterization of novel QDM-based chromophores 1-3, which exhibit unique photo-excited behavior and aromaticity. Extending the aromatic core with a biphenyl/phenanthryl- and a pyrrolo-fragment led to reducing the optoelectronic bandgap and modulating the photophysics QDM 1-3. Yet, QDM 2 and 3 suffer from "aromaticity imbalance" and become relatively unstable compared to the parent compound QDM 1. Further assessment of local aromaticity using computational tools revealed that the pseudo-quinoidal ring B is the main driving force allowing to easily populate the excited triplet state of these chromophores. The present study provides complementary guidelines for designing novel non-classical poly-aromatic systems.
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Affiliation(s)
- Guang Yang
- Department of Chemistry, University of Illinois at Chicago, Chicago, IL 60607, USA
| | - Young Ju Yun
- Department of Chemistry, University of Illinois at Chicago, Chicago, IL 60607, USA
| | - Francesca Peccati
- Center for Cooperative Research in Biosciences (CIC bioGUNE), Basque Research and Technology Alliance (BRTA), Bizkaia Technology Park, Building 800, 48160, Derio, Spain
| | - Abdelqader M Jamhawi
- Department of Chemistry, University of Illinois at Chicago, Chicago, IL 60607, USA
| | - Nareshbabu Kamatham
- Department of Chemistry, University of Illinois at Chicago, Chicago, IL 60607, USA
| | - Steffen Jockusch
- Department of Chemistry & Center for Photochemical Sciences, Bowling Green State University, Bowling Green, OH 43403, USA
| | - Gonzalo Jiménez-Osés
- Center for Cooperative Research in Biosciences (CIC bioGUNE), Basque Research and Technology Alliance (BRTA), Bizkaia Technology Park, Building 800, 48160, Derio, Spain
- Ikerbasque, Basque Foundation for Science, 48013, Bilbao, Spain
| | - A Jean-Luc Ayitou
- Department of Chemistry, University of Illinois at Chicago, Chicago, IL 60607, USA
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7
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Terence Blaskovits J, Garner MH, Corminboeuf C. Symmetry-Induced Singlet-Triplet Inversions in Non-Alternant Hydrocarbons. Angew Chem Int Ed Engl 2023; 62:e202218156. [PMID: 36786076 DOI: 10.1002/anie.202218156] [Citation(s) in RCA: 15] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2022] [Revised: 02/09/2023] [Accepted: 02/13/2023] [Indexed: 02/15/2023]
Abstract
Molecules with inversion of the singlet and triplet excited-state energies are highly promising for the development of organic light-emitting diodes (OLEDs). To date, azaphenalenes are the only class of molecules where these inversions have been identified. Here, we screen a curated database of organic crystal structures to identify existing compounds for violations of Hund's rule in the lowest excited states. We identify two further classes with this behavior. The first, a class of zwitterions, has limited relevance to molecular emitters as the singlet-triplet inversions occur in the third excited singlet state. The second class consists of two D2h -symmetry non-alternant hydrocarbons, a fused azulene dimer and a bicalicene, whose lowest excited singlet states violate Hund's rule. Due to the connectivity of the polycyclic structure, they achieve this symmetry through aromatic stabilization. These hydrocarbons show promise as the next generation of building blocks for OLED emitters.
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Affiliation(s)
- J Terence Blaskovits
- Laboratory for Computational Molecular Design, Institute of Chemical Sciences and Engineering, École Polytechnique Fedéralé de Lausanne (EPFL), 1015, Lausanne, Switzerland
| | - Marc H Garner
- Laboratory for Computational Molecular Design, Institute of Chemical Sciences and Engineering, École Polytechnique Fedéralé de Lausanne (EPFL), 1015, Lausanne, Switzerland
| | - Clémence Corminboeuf
- Laboratory for Computational Molecular Design, Institute of Chemical Sciences and Engineering, École Polytechnique Fedéralé de Lausanne (EPFL), 1015, Lausanne, Switzerland
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9
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Swathi Krishna PE, Dev VV, Ramakrishnan R, Hariharan M. Retaining Hückel Aromaticity in the Triplet Excited State of Azobenzene. Chemphyschem 2022; 23:e202200045. [PMID: 35532154 DOI: 10.1002/cphc.202200045] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2022] [Revised: 03/09/2022] [Indexed: 02/04/2023]
Abstract
The implication of the potential concept of aromaticity in the relaxed lowest triplet state of azobenzene, an efficient molecular switch, using elementary aromaticity indices based on magnetic, electronic, and geometric criteria has been discussed. Azobenzene exhibits a major Hückel aromatic character retained in the diradical lowest relaxed triplet state (T1 ) by virtue of a twisted geometry with partial delocalization of unpaired electrons in the perpendicular p-orbitals of two nitrogen atoms to the corresponding phenyl rings. The computational analysis has been expanded further to stilbene and N-diphenylmethanimine for an extensive understanding of the effect of closed-shell Hückel aromaticity in double-bond-linked phenyl rings. Our analysis concluded that stilbene has Hückel aromatic character in the relaxed T1 state and N-diphenylmethanimine has a considerable Hückel aromaticity in the phenyl ring near the carbon atom while a paramount Baird aromaticity in the phenyl ring near the nitrogen atom of the C=N double bond. The results reveal the application of excited-state aromaticity as a general tool for the design of molecular switches.
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Affiliation(s)
- P E Swathi Krishna
- School of Chemistry, Indian Institute of Science Education and Research Thiruvananthapuram, Thiruvananthapuram, Kerala 695551, India
| | - Vivek V Dev
- School of Chemistry, Indian Institute of Science Education and Research Thiruvananthapuram, Thiruvananthapuram, Kerala 695551, India
| | - Remya Ramakrishnan
- School of Chemistry, Indian Institute of Science Education and Research Thiruvananthapuram, Thiruvananthapuram, Kerala 695551, India
| | - Mahesh Hariharan
- School of Chemistry, Indian Institute of Science Education and Research Thiruvananthapuram, Thiruvananthapuram, Kerala 695551, India
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Baranac-Stojanović M, Stojanović M, Aleksić J. Revival of Hückel Aromatic (Poly)benzenoid Subunits in Triplet State Polycyclic Aromatic Hydrocarbons by Silicon Substitution. Chem Asian J 2021; 17:e202101261. [PMID: 34964285 DOI: 10.1002/asia.202101261] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2021] [Revised: 12/22/2021] [Indexed: 11/08/2022]
Abstract
By employing density functional theory (DFT) calculations we show that mono- and disilicon substitution in polycyclic aromatic hydrocarbons, having two to four benzene units, quenches their triplet state antiaromaticity by creating Hückel aromatic (poly)benzenoid subunit(s) and weakly antiaromatic, or almost nonaromatic silacycle. Therefore, such systems are predicted to be globally aromatic in both the ground state and the first excited triplet state. Putting the silicon atom(s) into various positions of a hydrocarbon provides an opportunity to tune the singlet-triplet energy gaps. They depend on the global aromaticity degree which, in turn, depends on the type of aromatic carbocyclic subunit(s) and the extent of their aromaticity. On the basis of the set of studied compounds, some preliminary rules on how to regulate the extent of global, semiglobal and local aromaticity are proposed. The results of this work extend the importance of Hückel aromaticity concept to excited triplet states which are usually characterized by the Baird type of (anti)aromaticity.
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Affiliation(s)
- Marija Baranac-Stojanović
- Faculty of Chemistry, University of Belgrade, Organic Chemistry, Studentski trg 16, 11000, Belgrade, SERBIA
| | - Milovan Stojanović
- Institute of Chemistry Technology and Metallurgy: Institut za hemiju tehnologiju i metalurgiju, Center for Chemistry, SERBIA
| | - Jovana Aleksić
- Institute of Chemistry Technology and Metallurgy: Institut za hemiju tehnologiju i metalurgiju, Center for Chemistry, SERBIA
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Kim J, Oh J, Osuka A, Kim D. Porphyrinoids, a unique platform for exploring excited-state aromaticity. Chem Soc Rev 2021; 51:268-292. [PMID: 34879124 DOI: 10.1039/d1cs00742d] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Recently, Baird (anti)aromaticity has been referred to as a description of excited-state (anti)aromaticity. With the term of Baird's rule, recent studies have intensively verified that the Hückel aromatic [4n + 2]π (or antiaromatic [4n]π) molecules in the ground state are reversed to give Baird aromatic [4n]π (or Baird antiaromatic [4n + 2]π) molecules in the excited states. Since the Hückel (anti)aromaticity has great influence on the molecular properties and reaction mechanisms, the Baird (anti)aromaticity has been expected to act as a dominant factor in governing excited-state properties and processes, which has attracted intensive scientific investigations for the verification of the concept of reversed aromaticity in the excited states. In this scientific endeavor, porphyrinoids have recently played leading roles in the demonstration of the aromaticity reversal in the excited states and its conceptual development. The distinct structural and electronic nature of porphyhrinoids depending on their (anti)aromaticity allow the direct observation of excited-state aromaticity reversal, Baird's rule. The explicit experimental demonstration with porphyrinoids has contributed greatly to its conceptual development and application in novel functional organic materials. Based on the significant role of porphyrinoids in the field of excited-state aromaticity, this review provides an overview of the experimental verification of the reversal concept of excited-state aromaticity by porphyrinoids and the recent progress on its conceptual application in novel functional molecules.
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Affiliation(s)
- Jinseok Kim
- Department of Chemistry, Yonsei University, Seoul 03722, Korea.
| | - Juwon Oh
- Department of Chemistry, Soonchunhyang University, Asan-si 31538, Korea.
| | - Atsuhiro Osuka
- Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
| | - Dongho Kim
- Department of Chemistry, Yonsei University, Seoul 03722, Korea.
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12
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Diaz-Andres A, Casanova D. Benzene Excimer and Excited Multimers: Electronic Character, Interaction Nature, and Aromaticity. J Phys Chem Lett 2021; 12:7400-7408. [PMID: 34328333 DOI: 10.1021/acs.jpclett.1c01908] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
In this Letter we analyze the forces involved in the formation of the benzene excimer and its electron structure, and (anti)aromatic character. We extend our study to excited states in molecular aggregates, the triplet excimer and the benzene-tricyanobenzene exciplex. Electronic wave functions are decomposed in terms of localized excitations and ion-pair configurations through diabatization, and we show that excimer (anti)aromaticity can be described as the linear combination of ground, excited, and ionic molecular states. Our analysis concludes that the benzene excimer must be characterized as antiaromatic, with weaker antiaromaticity than the molecular excited singlet. Moreover, we define a model electronic Hamiltonian for the excimer state and we use it as a building block for the extrapolation of electronic Hamiltonians in molecular aggregates. Benzene multimers present a nonuniform (anti)aromatic character, with the center of the column being antiaromatic and the edges behaving as aromatic. The implications of this work go beyond the study of the excimer, providing a general framework for the calculation and characterization of excited states in aggregates.
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Affiliation(s)
- Aitor Diaz-Andres
- Donostia International Physics Center (DIPC), 20018 Donostia, Euskadi, Spain
| | - David Casanova
- Donostia International Physics Center (DIPC), 20018 Donostia, Euskadi, Spain
- IKERBASQUE, Basque Foundation for Science, 48009 Bilbao, Euskadi, Spain
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13
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Morgan J, Yun YJ, Ayitou AJL. Estimation of Singlet Oxygen Quantum Yield Using Novel Green-Absorbing Baird-type Aromatic Photosensitizers †. Photochem Photobiol 2021; 98:57-61. [PMID: 34228818 DOI: 10.1111/php.13483] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2021] [Revised: 05/30/2021] [Accepted: 07/04/2021] [Indexed: 12/20/2022]
Abstract
We report two new organic green-absorbing singlet oxygen (1 O2 ) photosensitizers: Quinoidal naphthyl thioamide (QDM) and bis-iodol-dipyrrolonaphthyridine-dione (I2 -DPND), with triplet energies of 40.8 and 47.5 kcal mol-1 (at 77 K in a glassy matrix) , respectively. The UV-vis absorption and emission characteristics of QDM and I2 -DPND are similar to other commercially available organic 1 O2 photosensitizers such as Rose Bengal, which was used as standard/reference to estimate the 1 O2 quantum yield (Φ∆ ) of the chromophores under study. Using 9,10-diphenylanthracene (DPA) as an 1 O2 quencher, we estimated the Φ∆ ≈ 67-85% for QDM and Φ∆ ≈ 25-32% for I2 -DPND. The discrepancy in the Φ∆ values could be explained by the apparent photo-decomposition of the later dye. Nevertheless, the high Φ∆ value for QDM is unprecedented, as this chromophore exhibits relatively low structural complexity and could further be derivatized to create novel photodynamic agents.
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Affiliation(s)
- Jayla Morgan
- Department of Chemistry, Illinois Institute of Technology, Chicago, IL, USA
| | - Young Ju Yun
- Department of Chemistry, Illinois Institute of Technology, Chicago, IL, USA.,Department of Chemistry, University of Illinois at Chicago, Chicago, IL, USA
| | - A Jean-Luc Ayitou
- Department of Chemistry, Illinois Institute of Technology, Chicago, IL, USA.,Department of Chemistry, University of Illinois at Chicago, Chicago, IL, USA
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Pino-Rios R, Báez-Grez R, Solà M. Acenes and phenacenes in their lowest-lying triplet states. Does kinked remain more stable than straight? Phys Chem Chem Phys 2021; 23:13574-13582. [PMID: 34109330 DOI: 10.1039/d1cp01441b] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The larger stability of phenacenes compared to their acene isomers in their ground states is attributed to the larger aromaticity of the former. To our knowledge the relative stability of acenes and phenacenes in their lowest-lying triplet states (T1) has not been discussed yet. Using unrestricted density functional theory calculations, our results show that for the smallest members of the series, acenes in their T1 states are more stable than the corresponding phenacenes. However, when the number of the rings (n) involved increases, the energy difference is reduced and for n > 12, phenacenes become more stable than acenes in their T1 states. To rationalize this trend, we analyze the aromaticity of acenes and phenacenes using a set of aromaticity descriptors. We find that in the T1 states of both acenes and phenacenes, the outer rings form aromatic Clar π-sextets. In acenes, delocalization of spin density in the central rings leads to the preferred formation of the largest antiaromatic diradical. Resonant structures in the form of antiaromatic diradical Baird π-octadectets and π-tetradectets are the major contributors, while the smaller ones, such as π-doublets and π-sextets, contribute the least. In phenacenes, structures with diradical antiaromatic Baird π-sextets in some of the central rings contribute the most. These results are relevant to understand the (anti)aromaticity of larger polycyclic aromatic hydrocarbons in their triplet states.
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Affiliation(s)
- Ricardo Pino-Rios
- Laboratorio de Química Teórica, Facultad de Química y Biología, Universidad de Santiago de Chile (USACH), Región Metropolitana, Chile.
| | - Rodrigo Báez-Grez
- Computational and Theoretical Chemistry Group, Departamento de Ciencias Químicas, Facultad de Ciencias Exactas, Universidad Andres Bello, República 498, Santiago, Chile
| | - Miquel Solà
- Institut de Química Computacional i Catàlisi and Departament de Química, Universitat de Girona, 17003 Girona, Catalonia, Spain.
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Zeng W, El Bakouri O, Szczepanik DW, Bronstein H, Ottosson H. Excited state character of Cibalackrot-type compounds interpreted in terms of Hückel-aromaticity: a rationale for singlet fission chromophore design. Chem Sci 2021; 12:6159-6171. [PMID: 33996014 PMCID: PMC8098681 DOI: 10.1039/d1sc00382h] [Citation(s) in RCA: 26] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2021] [Accepted: 03/24/2021] [Indexed: 12/23/2022] Open
Abstract
The exact energies of the lowest singlet and triplet excited states in organic chromophores are crucial to their performance in optoelectronic devices. The possibility of utilizing singlet fission to enhance the performance of photovoltaic devices has resulted in a wide demand for tuneable, stable organic chromophores with wide S1-T1 energy gaps (>1 eV). Cibalackrot-type compounds were recently considered to have favorably positioned excited state energies for singlet fission, and they were found to have a degree of aromaticity in the lowest triplet excited state (T1). This work reports on a revised and deepened theoretical analysis taking into account the excited state Hückel-aromatic (instead of Baird-aromatic) as well as diradical characters, with the aim to design new organic chromophores based on this scaffold in a rational way starting from qualitative theory. We demonstrate that the substituent strategy can effectively adjust the spin distribution on the chromophore and thereby manipulate the excited state energy levels. Additionally, the improved understanding of the aromatic characters enables us to demonstrate a feasible design strategy to vary the excited state energy levels by tuning the number and nature of Hückel-aromatic units in the excited state. Finally, our study elucidates the complications and pitfalls of the excited state aromaticity and antiaromaticity concepts, highlighting that quantitative results from quantum chemical calculations of various aromaticity indices must be linked with qualitative theoretical analysis of the character of the excited states.
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Affiliation(s)
- Weixuan Zeng
- Department of Chemistry, University of Cambridge Cambridge CB2 1EW UK
| | - Ouissam El Bakouri
- Department of Chemistry - Ångström Laboratory, Uppsala University 751 20 Uppsala Sweden
| | - Dariusz W Szczepanik
- Department of Theoretical Chemistry, Faculty of Chemistry, Jagiellonian University Gronostajowa, 2 30-387 Kraków Poland
- Institut de Quìmica Computacional i Catàlisi, Departament de Química, Universitat de Girona C/ Maria Aurèlia Capmany, 69 17003 Girona Catalonia Spain
| | - Hugo Bronstein
- Department of Chemistry, University of Cambridge Cambridge CB2 1EW UK
- Cavendish Laboratory, University of Cambridge Cambridge CB3 0HE UK
| | - Henrik Ottosson
- Department of Chemistry - Ångström Laboratory, Uppsala University 751 20 Uppsala Sweden
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