Five decades of mechanistic and exploratory organic photochemistry

2006 ◽  
Vol 78 (12) ◽  
pp. 2193-2203 ◽  
Author(s):  
Howard E. Zimmerman
Keyword(s):  
Excited State ◽  
Electronic Structures ◽  
Personal Perspective ◽  
Photochemical Reactivity ◽  
The Third ◽  
Organic Photochemistry

This exposition summarizes a personal perspective on past and current developments in organic photochemistry. It comprises three portions. The first section describes the beginnings of our photochemical studies and how it was possible to relate photochemical reactivity to excited-state electronic structures. The second selectively relates some of the reactions and concepts developed in the intermediate years. Finally, the third portion describes our recent research.

Near-Infrared Combination and Overtone Bands of CH in CHX3, CHX2—CHX2, and CHX2—CX2—CHX2

2005 ◽  
Vol 59 (11) ◽  
pp. 1393-1398 ◽  
Author(s):  
Reikichi Iwamoto ◽  
Akishi Nara ◽  
Toshihiko Matsuda
Keyword(s):  
Excited State ◽  
Near Infrared ◽  
Present Report ◽  
Spectral Characteristics ◽  
The Other ◽  
Coupled Modes ◽  
Third Order ◽  
The Third ◽  
Combination Bands ◽  
Deformation Modes

In the present report we studied spectral characteristics of the near-infrared combination and overtone bands of CH vibrations of a CH sequence. The near-infrared bands of the CH in CHX3 (X, halogen), which were interpreted in terms of the CH stretching and CH deformation fundamentals without any ambiguity, typically showed how the frequency and intensity of a combination or an overtone depend on the vibrational excited state. In the CH–C–CH of CHX2CX2CHX2, the vibrations of one CH are isolated from those of the other CH, and the combination and overtone bands were similarly interpreted as those of the CH, although each of the combination bands was split into two because of non-degeneracy of the CH deformation. In the CH–CH of CHX2CHX2, the CH deformations only have coupled modes. The first combination showed four narrowly separate bands, which were reasonably interpreted on the basis of the CH stretching and the coupled CH deformation modes. We demonstrated that the first combination of coupled modes as well as the combination of up to, at least, the third order of isolated modes have the nature of the characteristic bands.

scholarly journals The Photochemical Reactivity of Some Benzoylthiophenes. III. The Effect of an Adjacent Methyl Group on the Excited State Reactivity of 2-Benzoylthiophene

1975 ◽  
Vol 53 (1) ◽  
pp. 1-11 ◽  
Author(s):  
D. R. Arnold ◽  
B. M. Clarke Jr.
Keyword(s):  
Excited State ◽  
Carbonyl Group ◽  
Emission Spectra ◽  
Ultraviolet Absorption ◽  
Photochemical Reactivity ◽  
Methyl Group ◽  
Partial Energy ◽  
Phosphorescence Emission ◽  
Π State

The ultraviolet absorption and phosphorescence emission spectra of 2-(2-methylbenzoyl) thiophene (1), 2-benzoyl-3-methylthiophene (2), 2-benzoyl-4-methylthiophene (3), and 2-benzoyl-5-methylthiophene (4) are reported and analyzed. Partial energy diagrams are constructed. The lowest triplet is assigned as a π,π* state of the 2-thienoyl chromophore in every case. Photocycloaddition of isobutylene to the carbonyl group was observed with 1 and 2. The oxetanes are thermally unstable; olefins 1-(2-thienyl)-1-(2-methylphenyl)-2-methylpropene (from 1) and 1-phenyl-1-(2-(3-methylthienyl))-2-methylpropene (from 2) were formed and characterized. Irradiation of 1 and 2 in O-deuteromethanol did not lead to incorporation of deuterium; no reaction was observed. These results are discussed in terms of the existing generalizations potentially useful for predicting photochemical reactivity.

Enhancement of third-order nonlinear optical properties of HMTA stabilized pure and doped ZnS nanoparticles and their electronic structures

2018 ◽  
Vol 27 (02) ◽  
pp. 1850016 ◽  
Author(s):  
K. Vijai Anand ◽  
G. Vinitha ◽  
Sanjeev Gautam ◽  
K. H. Chae ◽  
R. Mohan ◽  
...  
Keyword(s):  
Transition Metals ◽  
Electronic Structures ◽  
Nonlinear Optical ◽  
Zns Nanoparticles ◽  
Third Order ◽  
Tetrahedral Symmetry ◽  
Nonlinear Optical Susceptibility ◽  
Nlo Properties ◽  
The Third ◽  
Mn Doped

This study reports the third-order nonlinear optical (NLO) properties of hexamethylenetetramine (HMTA) stabilized pure and transition metals (Cu, Co and Mn) doped ZnS nanoparticles (NPs) and their electronic structures. The third-order NLO properties of pure and transition metals (Cu, Co and Mn) doped ZnS NPs were measured by [Formula: see text]-scan technique. From these measurements, the pure and doped ZnS samples exhibit negative nonlinearity i.e., self-defocusing. The open aperture [Formula: see text]-scan measurement shows saturated absorption within the medium. The prepared pure and doped ZnS samples exhibit nonlinear refractive index of the order of 10[Formula: see text][Formula: see text](cm2/W), nonlinear absorption (NLA) coefficient of the order of 10[Formula: see text][Formula: see text]cm/W and nonlinear optical susceptibility of the order of 10[Formula: see text][Formula: see text]esu. The electronic structures of these ZnS NPs were investigated using near edge X-ray absorption fine structure (NEXAFS) measurements at the C K-, N K- and Co L[Formula: see text]-edges. The C K- and N K-edges XANES spectra reveal the appearance of several spectral features in the range 285–290[Formula: see text]eV and 390–430[Formula: see text]eV respectively. The Co L[Formula: see text]-edge NEXAFS spectrum exhibits multiplet absorption lines similar to those of Co[Formula: see text] ions coordinated in tetrahedral symmetry with four sulfur nearest neighbors. These results clearly demonstrate that divalent Co ions substitute Zn sites. From the Raman spectra, the appearance of multiple resonance Raman peaks indicates that the prepared ZnS samples have good optical quality.

Organic photochemistry. XXVII. Electronically excited state structures

1967 ◽  
Vol 89 (25) ◽  
pp. 6589-6595 ◽  
Author(s):  
Howard E. Zimmerman ◽  
Roger W. Binkley ◽  
John J. McCullough ◽  
Gary A. Zimmerman
Keyword(s):  
Excited State ◽  
Electronically Excited State ◽  
Organic Photochemistry ◽  
Electronically Excited

Spontaneous Tunnel Transitions Induced by Redistribution of Trapped Electrons over Impurity Centers

1983 ◽  
Vol 38 (9) ◽  
pp. 959-962
Author(s):  
A. A. Berezin
Keyword(s):  
Excited State ◽  
Charge State ◽  
Ground State ◽  
Low Energy ◽  
Energy Photon ◽  
Impurity Site ◽  
The Third ◽  
Tunnel Transition ◽  
Extra Electron ◽  
Impurity Centers

Abstract A system of polyvalent impurity centers in a semiconductor (i.e. Au-centers in Si) is con-sidered. The ground state of the impurity pair Au-(a) + Au° (b), where an extra electron is localized on the site a, may be turned into an excited state due to a change of the charge state of a third nearby impurity site. This happens because of different shifts of the Au--level at sites a and b due to their different distances from the third center. As a result, the original pair is able to reach a new ground state Au° (a) + Au- (b) through a slow spontaneous tunnel transition. The probability of this transition, when it is accompanied by an emission of a low energy photon, is calculated explicitly.

Exotic structure of the third excited state in 21Na

2005 ◽  
Vol 50 (23) ◽  
pp. 2677
Author(s):  
Xihan LI
Keyword(s):  
Excited State ◽  
The Third
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