Intramolecular sensitization within steroids: Excited-state interaction of C-17 α and β carbon–bromine bonds with a C-6 carbonyl group

2003 ◽  
Vol 81 (6) ◽  
pp. 660-668 ◽  
Author(s):  
Wen-Shan Li ◽  
Lokman Torun ◽  
Harry Morrison
Keyword(s):  
Energy Transfer ◽  
Excited State ◽  
Carbonyl Group ◽  
Singlet State ◽  
State Interaction ◽  
Excited Singlet State ◽  
Excited Singlet

The synthesis, photochemistry, and photophysics of 17α-bromo-3α-(triphenylsilyloxy)-5α-androstan-6-one (1) and 17β-bromo-3β-(triphenylsilyloxy)-5α-androstan-6-one (2) have been studied in aqueous tetrahydrofuran. The 17α-bromo isomer gives evidence (reduced ϕf, τ1, and ϕisc for the ketone) for interaction between the ketone and C–Br moieties in the excited singlet state. Some photodehalogenation is also observed upon excitation of the ketone chromophore. This interaction seems to be absent or minimal for the 17β-bromo isomer.Key words: photodehalogenation, bromosteroid, ketosteroid, intramolecular singlet–singlet energy transfer (ISSET).

Excited state spectroscopy of 1,5‐naphthyridine: Identification of the lowest energy excited singlet state as 1Bg(1nπ*)

1983 ◽  
Vol 79 (8) ◽  
pp. 3639-3644 ◽  
Author(s):  
David W. Boldridge ◽  
Gary W. Scott
Keyword(s):  
Excited State ◽  
Singlet State ◽  
Excited Singlet State ◽  
Excited Singlet

Permanent Dipole Moment and Polarizability of a Gass of Merocyanine Dyes in Their Ground and First Excited Singlet State

1983 ◽  
Vol 38 (9) ◽  
pp. 995-1002 ◽  
Author(s):  
Wolfram Baumann
Keyword(s):  
Dipole Moment ◽  
Excited State ◽  
Electric Field ◽  
Field Model ◽  
Singlet State ◽  
Excited Singlet State ◽  
Permanent Dipole Moment ◽  
Excited Singlet ◽  
Reaction Field ◽  
Merocyanine Dyes

Abstract The permanent dipole moment of a class of merocyanine dyes in their ground and first excited singlet state has been determined studying the influence of an external electric field on the absorption of the compounds in various solvents. Evaluation of the experimental results on the basis of the Onsager reaction field model also gives values for the polarizability in the ground and excited state, the latter approaches the value of a respective conducting ellipsoid with the longer chainlength molecules.

Excited State Properties of Peridinin:  Observation of a Solvent Dependence of the Lowest Excited Singlet State Lifetime and Spectral Behavior Unique among Carotenoids

1999 ◽  
Vol 103 (41) ◽  
pp. 8751-8758 ◽  
Author(s):  
James A. Bautista ◽  
Robert E. Connors ◽  
B. Bangar Raju ◽  
Roger G. Hiller ◽  
Frank P. Sharples ◽  
...  
Keyword(s):  
Excited State ◽  
Singlet State ◽  
Excited Singlet State ◽  
Excited Singlet ◽  
Spectral Behavior ◽  
Solvent Dependence

The structure, photochemical reactivity, and photophysical properties of adamantyl X-substituted aryl ethers and a comparison with the alkyl groups, methyl, tert-butyl, and allyl

2005 ◽  
Vol 83 (9) ◽  
pp. 1237-1252 ◽  
Author(s):  
A L Pincock ◽  
J A Pincock
Keyword(s):  
Excited State ◽  
Rate Constants ◽  
Singlet State ◽  
Bond Cleavage ◽  
Photophysical Properties ◽  
Excited Singlet State ◽  
Quantum Yields ◽  
Aryl Ether ◽  
Excited Singlet ◽  
Aryl Ethers

The structure, photophysical properties, and photochemistry of the adamantyl aryl ethers 1 in both methanol and cyclohexane have been examined. UV absorption spectra, 13C NMR chemical shifts, X-ray structures, and Gaussian calculations (B3LYP/6-31G(d)) indicate that these ethers adopt a 90° conformer in the ground state. In contrast, fluorescence spectra, excited singlet state lifetimes, and calculations (TDDFT) indicated a 0° conformer is preferred in the first excited singlet state S1. Irradiation in either solvent results in the formation of adamantane and the corresponding phenol as the major products, both derived from radical intermediates generated by homolytic cleavage of the ether bond. The 4-cyano substituted ether 1j was the only one to form the ion-derived product, 1-methoxyadamantane (16% yield), on irradiation in methanol. Rate constants of bond cleavage for these ethers from S1 were estimated by two different methods by comparison with the unreactive anisoles 2, but the effect of substituents was too small to determine structure–reactivity correlations. The temperature dependence of the quantum yields of the fluorescence of the unsub stituted, 4-methoxy and 4-cyano derivatives of 1 and 2 were also determined. These results indicated that the activated process for 1 was mainly bond cleavage for the 4-cyano substrate whereas for 2, it was internal conversion and intersystem crossing. Key words: aryl ether photochemistry, fluorescence, excited-state rate constants, excited-state temperature effects.

Photochemistry of Nitracrine and its Analogues: Acridine Derivatives as Electron Donors

1984 ◽  
Vol 39 (2) ◽  
pp. 195-200 ◽  
Author(s):  
J. Biedrzycki ◽  
J. Błażejowski ◽  
J. Szychliński ◽  
A. Ledòchowski
Keyword(s):  
Electron Transfer ◽  
Excited State ◽  
Fluorescence Quenching ◽  
Triplet State ◽  
Uv Radiation ◽  
Electron Acceptor ◽  
Singlet State ◽  
Electron Donors ◽  
Excited Singlet State ◽  
Excited Singlet

Studies on the electron transfer in the excited state from electron donors: acridine, 9- aminoacridine and its derivatives, including nitracrine and its isomers, to CCl4 as a suitable electron acceptor, were undertaken. UV radiation (λ= 366 nm), absorbed only by acridine bases, generates CI- ions. The fluorescence quenching measurements indicate that no interaction appears between molecules of acridine bases in the excited singlet state and CCl4 molecule. A scheme of photochemical processes is proposed which assumes that the triplet state of the base molecule is the reactive one.

Excited state reactivity of aza aromatics. I. Basicity of 3-styrylpyridines in the first excited singlet state

1973 ◽  
Vol 77 (5) ◽  
pp. 601-604 ◽  
Author(s):  
G. Favaro ◽  
U. Mazzucato ◽  
F. Masetti
Keyword(s):  
Excited State ◽  
Singlet State ◽  
Excited Singlet State ◽  
Excited Singlet
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