Photoinduced reaction. 142. Intramolecular hydrogen abstraction from triplet states of 2,4,6-triisopropylbenzophenones: importance of hindered rotation in excited states

1983 ◽  
Vol 105 (6) ◽  
pp. 1590-1597 ◽  
Author(s):  
Yoshikatsu Ito ◽  
Hiroaki Nishimura ◽  
Yasutoshi Umehara ◽  
Yutaka Yamada ◽  
Mutsuto Tone ◽  
...  
Keyword(s):  
Excited States ◽  
Hydrogen Abstraction ◽  
Triplet States ◽  
Hindered Rotation ◽  
Photoinduced Reaction ◽  
Intramolecular Hydrogen

The photochemical reactivity of some benzoylthiophenes. IV. The effect of an adjacent methyl group on the excited state reactivity of 3-benzoylthiophene

1978 ◽  
Vol 56 (15) ◽  
pp. 1970-1984 ◽  
Author(s):  
D. R. Arnold ◽  
C. P. Hadjiantoniou
Keyword(s):  
Hydrogen Abstraction ◽  
Thiophene Ring ◽  
Emission Spectra ◽  
Photochemical Reactions ◽  
Triplet States ◽  
Photochemical Reactivity ◽  
Methyl Group ◽  
State Diagrams ◽  
Phosphorescence Emission ◽  
Intramolecular Hydrogen

The electronic absorption and phosphorescence emission spectra and the photochemical reactivity of several methyl-3-benzoylthiophenes (2- and 4-methyl-3-benzoylthiophene (1, 2), 2,5-dimethyl-3-benzoylthiophene (3), and 3-(2-methylbenzoyl)thiophene (4)) have been studied. Partial state diagrams have been constructed. The lowest energy absorption in hexane solution in every case is the carbonyl n → π* transition. The two lowest triplet states of these ketones are close in energy and, in fact, the nature of the emitting triplet (n,π* or π,π*) depends upon the position of methyl substitution and upon the solvent. The photochemical reactions studied include intramolecular hydrogen abstraction (revealed by deuterium exchange in the adjacent methyl group upon irradiation in perdeuteriomethanol solution), photocycloaddition of dimethyl acetylenedicarboxylate to the thiophene ring, and photocycloaddition of isobutylene to the carbonyl group. Generalizations, potentially useful for predicting photochemical reactivity of these and other aromatic ketones are summarized.

Photolysereaktionen mit Komplexen des Typs CpFe(CO)2R (R = Me, Et, Ph)+ / Photolytic Reactions with Complexes of the Type CpFe(CO)2R (R = Me, Et, Ph)+

1979 ◽  
Vol 34 (8) ◽  
pp. 1070-1077 ◽  
Author(s):  
H. G. Alt ◽  
M. Herberhold ◽  
B. H. Edwards
Keyword(s):  
Mass Spectra ◽  
Hydrogen Abstraction ◽  
Carbonyl Groups ◽  
Subsequent Reaction ◽  
Methyl Group ◽  
Hydrocarbon Solvents ◽  
Photoinduced Reaction ◽  
Intramolecular Hydrogen ◽  
Derivatives Of ◽  
C Nmr

Photolysis of CpFe(CO)2R complexes [R = Me (1a), Et (1b), Ph (1c)] in hydrocarbon solvents results in loss of the group R and formation of the binuclear compound [CpFe(CO)2]2 (2). In the case of 1a, the photogenerated methyl group reacts to give methane by intramolecular hydrogen abstraction from the Cp ring, or by intermolecular hydrogen abstraction either from the solvent or another methyl group. The photoinduced dealkylation of the ethyl compound 1b is explained by β-elimination (to give ethylene) and subsequent reaction of the hydrido intermediates thus formed with unchanged 1b (to give ethane). The photolysis of 1c leads to phenyl groups which abstract hydrogen from the solvent to give benzene; a noticeable amount of diphenyl is also observed if benzene is used as a solvent.In the presence of potential two-electron ligands L [L = PMe3, P(OMe)3], only the carbonyl groups of CpFe(CO)2Me (1a) are photolabile, and substituted derivatives of the type CpFe(CO)(L)Me [L = PMe3 (3a), P(OMe)3 (4a)] and CpFe(L)2Me [L = P(OMe)3 (5a)] are formed.The photoinduced reaction of CpFe(CO)2Me (1a) and diphenylacetylene in solution gives metallocyclic derivatives containing either one or two diphenylacetylene units. On the basis of the IR, the 1H and 13C NMR, and the mass spectra, the complex CpFe(CO)(Ph2C2-COMe) (6a) is assigned a structure containing a vinyl-ketone unit in a five-membered metallocycle, while in CpFe(Ph4C4-COMe) (7a) a tetraphenylbutadienyl group appears to be incorporated into a seven-membered metallocycle

Restriction of Access to Dark State: A New Mechanistic Model for Heteroatom-Containing AIE Systems

2019 ◽  
Author(s):  
Yujie Tu ◽  
Junkai Liu ◽  
Haoke Zhang ◽  
Qian Peng ◽  
Jacky W. Y. Lam ◽  
...  
Keyword(s):  
Excited States ◽  
Radiative Decay ◽  
Molecular Design ◽  
Mechanistic Model ◽  
Zinc Ion ◽  
Easy Access ◽  
Triplet States ◽  
Dark State ◽  
Ion Probe ◽  
Π State

Aggregation-induced emission (AIE) is an unusual photophysical phenomenon and provides an effective and advantageous strategy for the design of highly emissive materials in versatile applications such as sensing, imaging, and theragnosis. "Restriction of intramolecular motion" is the well-recognized working mechanism of AIE and have guided the molecular design of most AIE materials. However, it sometimes fails to be workable to some heteroatom-containing systems. Herein, in this work, we take more than one excited state into account and specify a mechanism –"restriction of access to dark state (RADS)" – to explain the AIE effect of heteroatom-containing molecules. An anthracene-based zinc ion probe named APA is chosen as the model compound, whose weak fluorescence in solution is ascribed to the easy access from the bright (π,π*) state to the closelying dark (n,π*) state caused by the strong vibronic coupling of the two excited states. By either metal complexation or aggregation, the dark state is less accessible due to the restriction of the molecular motion leading to the dark state and elevation of the dark state energy, thus the emission of the bright state is restored. RADS is found to be powerful in elucidating the photophysics of AIE materials with excited states which favor non-radiative decay, including overlap-forbidden states such as (n,π*) and CT states, spin-forbidden triplet states, which commonly exist in heteroatom-containing molecules.

scholarly journals Exploitation of Baird Aromaticity and Clar’s Rule for Tuning the Triplet Energies of Polycyclic Aromatic Hydrocarbons

Chemistry ◽  
2021 ◽  
Vol 3 (2) ◽  
pp. 532-549
Author(s):  
Felix Plasser
Keyword(s):  
Polycyclic Aromatic Hydrocarbons ◽  
Excited States ◽  
Aromatic Hydrocarbons ◽  
Density Functional ◽  
Materials Science ◽  
Chemical Shifts ◽  
Qualitative Description ◽  
Triplet States ◽  
Excitation Energies ◽  
Polycyclic Aromatic

Polycyclic aromatic hydrocarbons (PAH) are a prominent substance class with a variety of applications in molecular materials science. Their electronic properties crucially depend on the bond topology in ways that are often highly non-intuitive. Here, we study, using density functional theory, the triplet states of four biphenylene-derived PAHs finding dramatically different triplet excitation energies for closely related isomeric structures. These differences are rationalised using a qualitative description of Clar sextets and Baird quartets, quantified in terms of nucleus independent chemical shifts, and represented graphically through a recently developed method for visualising chemical shielding tensors (VIST). The results are further interpreted in terms of a 2D rigid rotor model of aromaticity and through an analysis of the natural transition orbitals involved in the triplet excited states showing good consistency between the different viewpoints. We believe that this work constitutes an important step in consolidating these varying viewpoints of electronically excited states.

scholarly journals Flavones’ and Flavonols’ Antiradical Structure–Activity Relationship—A Quantum Chemical Study

Antioxidants ◽  
2020 ◽  
Vol 9 (6) ◽  
pp. 461 ◽  
Author(s):  
Maciej Spiegel ◽  
Tadeusz Andruniów ◽  
Zbigniew Sroka
Keyword(s):  
Electron Transfer ◽  
Hydrogen Bonding ◽  
Density Functional ◽  
Hydrogen Abstraction ◽  
Quantum Chemical Study ◽  
Hydrogen Atom Transfer ◽  
Hydroxyl Group ◽  
Water Solvent ◽  
Intramolecular Hydrogen ◽  
Catechol Moiety

Flavonoids are known for their antiradical capacity, and this ability is strongly structure-dependent. In this research, the activity of flavones and flavonols in a water solvent was studied with the density functional theory methods. These included examination of flavonoids’ molecular and radical structures with natural bonding orbitals analysis, spin density analysis and frontier molecular orbitals theory. Calculations of determinants were performed: specific, for the three possible mechanisms of action—hydrogen atom transfer (HAT), electron transfer–proton transfer (ETPT) and sequential proton loss electron transfer (SPLET); and the unspecific—reorganization enthalpy (RE) and hydrogen abstraction enthalpy (HAE). Intramolecular hydrogen bonding, catechol moiety activity and the probability of electron density swap between rings were all established. Hydrogen bonding seems to be much more important than the conjugation effect, because some structures tends to form more intramolecular hydrogen bonds instead of being completely planar. The very first hydrogen abstraction mechanism in a water solvent is SPLET, and the most privileged abstraction site, indicated by HAE, can be associated with the C3 hydroxyl group of flavonols and C4’ hydroxyl group of flavones. For the catechol moiety, an intramolecular reorganization to an o-benzoquinone-like structure occurs, and the ETPT is favored as the second abstraction mechanism.

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