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.

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.

Excited-State Dynamics in the RNA Nucleotide Uridine 5’-Monophosphate Investigated by Femtosecond Broadband Transient Absorption Spectroscopy

2019 ◽  
Author(s):  
Matthew M. Brister ◽  
Carlos Crespo-Hernández
Keyword(s):  
Excited State ◽  
Excited States ◽  
Ground State ◽  
Transient Absorption ◽  
Electronic Energy ◽  
Transient Absorption Spectroscopy ◽  
Electronic Relaxation ◽  
Vibrationally Excited ◽  
Excited State Dynamics ◽  
Π State

<p></p><p> Damage to RNA from ultraviolet radiation induce chemical modifications to the nucleobases. Unraveling the excited states involved in these reactions is essential, but investigations aimed at understanding the electronic-energy relaxation pathways of the RNA nucleotide uridine 5’-monophosphate (UMP) have not received enough attention. In this Letter, the excited-state dynamics of UMP is investigated in aqueous solution. Excitation at 267 nm results in a trifurcation event that leads to the simultaneous population of the vibrationally-excited ground state, a longlived <sup>1</sup>n<sub>O</sub>π* state, and a receiver triplet state within 200 fs. The receiver state internally convert to the long-lived <sup>3</sup>ππ* state in an ultrafast time scale. The results elucidate the electronic relaxation pathways and clarify earlier transient absorption experiments performed for uracil derivatives in solution. This mechanistic information is important because long-lived nπ* and ππ* excited states of both singlet and triplet multiplicities are thought to lead to the formation of harmful photoproducts.</p><p></p>

Millimeter-Wave Spectrum of Ethyl Acetylene Centrifugal Distortion, Coriolis Interaction and Internal Rotation

1983 ◽  
Vol 38 (4) ◽  
pp. 447-451 ◽  
Author(s):  
J. Demaison ◽  
D. Boucher ◽  
J. Burie ◽  
A. Dubrulle
Keyword(s):  
Excited State ◽  
Internal Rotation ◽  
Plane Deformation ◽  
Wave Spectrum ◽  
Rotational Spectrum ◽  
Centrifugal Distortion ◽  
Coriolis Interaction ◽  
Methyl Group ◽  
First Excited State ◽  
Methyl Torsion

The rotational spectrum of ethyl acetylene has been investigated between 70 and 320 GHz. A Coriolis interaction has been found between the first excited state of the methyl torsion and the C - C = C in plane deformation. Splittings of transitions in the first excited torsional state show that the barrier hindering internal rotation of the methyl group amounts to 3271 cal/mole.

Spectroanalytical Parameters of Fungal Metabolites. IV. Moniliformin

1974 ◽  
Vol 57 (6) ◽  
pp. 1392-1396 ◽  
Author(s):  
J A Lansden ◽  
R J Clarkson ◽  
W C Neely ◽  
R J Cole ◽  
J W Kirksey
Keyword(s):  
Low Temperature ◽  
Aqueous Solutions ◽  
Ambient Temperature ◽  
Emission Spectrum ◽  
Potassium Salt ◽  
Emission Spectra ◽  
Fungal Metabolites ◽  
Fungal Metabolite ◽  
Fluorescence Excitation ◽  
Phosphorescence Emission

Abstract The spectral data for a novel fungal metabolite, moniliformin (potassium salt of 1-hydroxycyclobut- 1-ene-3,4-dione), are reported. The corrected ambient temperature fluorescence excitation and emission spectra are given and the quantum efficiency is calculated to be 5.32 × 10舓3. The uncorrected low temperature phosphorescence emission spectrum and lifetime are also reported. Other physical data are given to support spectral evidence that the molecule exists as a dimer in aqueous solutions.

Synthesis and properties of diads based on tetra-aryl porphyrins and ruthenium bis-terpyridine-type complexes

2001 ◽  
Vol 05 (07) ◽  
pp. 600-607 ◽  
Author(s):  
ISABELLE M. DIXON ◽  
JEAN-PAUL COLLIN
Keyword(s):  
Energy Transfer ◽  
Excited State ◽  
Fluorescence Quenching ◽  
Emission Spectra ◽  
Spectroscopic Properties ◽  
Free Base ◽  
Strong Electron ◽  
Transfer Processes ◽  
C Complex

Four diads consisting of a free-base or zinc aryl-porphyrin associated with two ruthenium(II) bis(terdentate) complexes (non-cyclometallated Ru ( N 6) or cylometallated Ru ( N 5 C )) have been synthesized. The strong electron-withdrawing properties of the Ru ( N 6) as compared to the Ru ( N 5 C ) complex have been illustrated by their electrochemical and spectroscopic properties. Emission spectra of the diads and the reference compounds have shown that very efficient fluorescence quenching occurs, probably by energy transfer processes from the porphyrin to the 3MLCT excited state of the ruthenium unit.

scholarly journals Use of a Hydrolytic Procedure and Spectrometric Methods in the Structure Elucidation of a Thiocarbonyl Analogue of Sildenafil Detected as an Adulterant in an Over-the-Counter Herbal Aphrodisiac

2009 ◽  
Vol 92 (5) ◽  
pp. 1336-1342 ◽  
Author(s):  
John C Reepmeyer ◽  
D Andr d'Avignon
Keyword(s):  
Dietary Supplement ◽  
Carbonyl Group ◽  
Minor Component ◽  
Pyrimidine Ring ◽  
Over The Counter ◽  
Methyl Group ◽  
Nmr Spectrometry ◽  
A Minor ◽  
Hydrolysis Of ◽  
Hydroxyethyl Group

Abstract A sildenafil-related compound was detected in an herbal dietary supplement marketed as an aphrodisiac. The compound was identified as an analogue of sildenafil in which the carbonyl group in the pyrimidine ring of sildenafil was substituted with a thiocarbonyl group, and the methyl group on the piperazine ring was substituted with a hydroxyethyl group. Based on this structure, the compound was named thiohydroxyhomosildenafil. The structure of the compound was established using HPLC/MS, UV spectrometry, electrospray ionization-MS/MS, NMR spectrometry, and a hydrolytic process. One key product of hydrolysis was 1-(2-hydroxyethyl)-piperazine; the identification of this product defined the amine portion of the compound. Another key product of hydrolysis was hydroxyhomosildenafil, generated by hydrolysis of the thiocarbonyl group to a carbonyl group (C S C O). Hydroxyhomosildenafil was detected as a minor component in the dietary supplement.

The electronic (yellow and violet) emission spectra of zirconium nitride

1976 ◽  
Vol 54 (12) ◽  
pp. 1216-1223 ◽  
Author(s):  
John K. Bates ◽  
T. M. Dunn
Keyword(s):  
High Resolution ◽  
Emission Spectra ◽  
Zirconium Nitride ◽  
Violet Emission ◽  
Isoelectronic Molecules ◽  
Π State

Two emission systems of ZrN have been obtained under high resolution at 5700 and 4050 Å. They are the A2Π → X2Σ and B2Σ → X2Σ systems analogous to those previously known for the isoelectronic molecules ScO and TiN.Analysis of the B2Σ → X2Σ system of the 90Zr14N species yields the values B0 = 0.4587 cm−1 and B0 = 0.4830 cm−1 for the B and X states respectively, while for the A2Π state (which is severely perturbed at low J for the 90Zr14N species) the90Zr15N species gives B0 = 0.4523 cm−1 and this yields a (calculated) value for the A state of the 90Zr14N species of 0.4799 cm−1.There are four perturbations in the 2Π3/2 state of both the Zr14N and Zr15N species.

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