E.S.R. of nitroxide radicals. II. Photosensitization of indoles, phenols, and thiols by a diphenylpyrazoline

1969 ◽  
Vol 22 (9) ◽  
pp. 1899 ◽  
Author(s):  
IH Leaver ◽  
GC Ramsay
Keyword(s):  
Excited State ◽  
Singlet Excited State ◽  
Nitroxide Radicals ◽  
Polar Solvents ◽  
Fluorescence Studies

Indoles, phenols, and thiols have been shown to undergo photosensitization by a diphenylpyrazoline in non-polar solvents. The intermediate radicals produced have been trapped using a nitrosoalkane scavenger, and the resulting nitroxide radicals examined in situ by e.s.r. Fluorescence studies of these systems have shown that indoles and phenols strongly quench the singlet excited state of the diphenyl- pyrazoline, whereas thiols have no effect.

scholarly journals Ultrafast intersystem crossing in xanthone from wavepacket dynamics

2021 ◽  
Author(s):  
Marc Alías Rodríguez ◽  
Coen De Graaf ◽  
Miquel Huix-Rotllant
Keyword(s):  
Excited State ◽  
Gas Phase ◽  
Internal Conversion ◽  
Singlet State ◽  
Minimum Energy ◽  
Intersystem Crossing ◽  
Singlet Excited State ◽  
Polar Solvents ◽  
Aromatic Ketones ◽  
Wavepacket Dynamics

Most aromatic ketones containing first-row elements undergo unexpectedly fast intersystem crossing in few tens of picoseconds and a quantum yield close to unity. Among them, xanthone (9H-xanthen-9-one) possesses one of the fastest singlet-triplet rates of ~1.5 ps. The exact mechanism of this unusually fast transition is still under debate. Here, we perform the wavepacket dynamics of the photochemistry of xanthone in the gas phase and in polar solvents. We show that xanthone follows El-Sayed's rule for intersystem crossing. From the second singlet excited state, the mechanism is sequential: (i) an internal conversion between singlets 1pipi*-1npi* (85 fs), (ii) an intersystem crossing 1npi*-3pipi* (2.0 ps), and (iii) an internal conversion between triplets 3pipi*-3npi* (602 fs). Each transfer finds its origin in a barrierless access to electronic state intersections. These intersections are close to minimum energy structures, allowing for efficient transitions from the initial singlet state to the triplets.

scholarly journals Chlorosulfuric acid-assisted production of functional 2D materials

2021 ◽  
Vol 5 (1) ◽  
Author(s):  
Mohsen Moazzami Gudarzi ◽  
Maryana Asaad ◽  
Boyang Mao ◽  
Gergo Pinter ◽  
Jianqiang Guo ◽  
...  
Keyword(s):  
Hexagonal Boron Nitride ◽  
2D Materials ◽  
Real Life ◽  
Large Area ◽  
Polar Solvents ◽  
Aspect Ratios ◽  
Two Dimensional Materials ◽  
Liquid Phase Exfoliation

AbstractThe use of two-dimensional materials in bulk functional applications requires the ability to fabricate defect-free 2D sheets with large aspect ratios. Despite huge research efforts, current bulk exfoliation methods require a compromise between the quality of the final flakes and their lateral size, restricting the effectiveness of the product. In this work, we describe an intercalation-assisted exfoliation route, which allows the production of high-quality graphene, hexagonal boron nitride, and molybdenum disulfide 2D sheets with average aspect ratios 30 times larger than that obtained via conventional liquid-phase exfoliation. The combination of chlorosulfuric acid intercalation with in situ pyrene sulfonate functionalisation produces a suspension of thin large-area flakes, which are stable in various polar solvents. The described method is simple and requires no special laboratory conditions. We demonstrate that these suspensions can be used for fabrication of laminates and coatings with electrical properties suitable for a number of real-life applications.

Amino derivatives of symmetric 1,3,5-triphenylbenzene. Nature of the polar singlet excited state.

1993 ◽  
Vol 176 (1) ◽  
pp. 195-213 ◽  
Author(s):  
G. Verbeek ◽  
S. Depaemelaere ◽  
M. Van der Auweraer ◽  
F.C. De Schryver ◽  
A. Vaes ◽  
...  
Keyword(s):  
Excited State ◽  
Singlet Excited State ◽  
Amino Derivatives ◽  
Derivatives Of

Thionine–graphene oxide covalent hybrid and its interaction with light

2017 ◽  
Vol 19 (22) ◽  
pp. 14412-14423 ◽  
Author(s):  
Ewelina Krzyszkowska ◽  
Justyna Walkowiak-Kulikowska ◽  
Sven Stienen ◽  
Aleksandra Wojcik
Keyword(s):  
Electron Transfer ◽  
Graphene Oxide ◽  
Excited State ◽  
Transfer Process ◽  
Singlet Excited State ◽  
Functionalized Graphene ◽  
Electron Transfer Process ◽  
Functionalized Graphene Oxide ◽  
Back Electron Transfer

Quenching of the thionine singlet excited state in covalently functionalized graphene oxide with an efficient back electron transfer process.

The photocycloaddition of dibenzoylmethanatoboron difluoride (DBMBF2) with conjugated enones and en-esters

1993 ◽  
Vol 71 (6) ◽  
pp. 846-854 ◽  
Author(s):  
Yuan L. Chow ◽  
Shi-Sen Wang ◽  
Xian-En Cheng
Keyword(s):  
Excited State ◽  
Charge Transfer ◽  
Ring Opening ◽  
Electron Donors ◽  
Head Orientation ◽  
Singlet Excited State ◽  
Methyl Substitution ◽  
Unsaturated Ketones ◽  
Dibenzoylmethanatoboron Difluoride

Dibenzoylmethanatoboron difluoride (DBMBF2), the BF2 complex of dibenzoylmethane, reacted from its singlet excited state with α,β-unsaturated ketones and esters to give 1,5-diketones by a [2+2] cycloaddition and ring-opening sequence in an analogous pathway to that observed in the photocycloaddition to olefins and dienes. The present photoreaction is unexpected since conjugated enones and en-esters are poor electron donors to comply with the previously proposed charge transfer requirement in DBMBF2 photoreactions. The photocycloaddition to these substrates was highly regioselective and stereoselective, giving the head-to-head orientation, which could be enhanced by α-methyl substitution; β-methyl substitution increased the alternate head-to-tail orientation. The photolysis of a mixture of DBMBF2 and a cyclic enone also caused the latter to dimerize to give head-to-head and head-to-tail dimers in significant yields. These photodimerizations were apparently caused by DBMBF2 sensitization. The mechanism of the sensitization is discussed.

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