scholarly journals Time-resolved laser flash photolysis study on transient reaction between excited triplet state of anthraquinone derivatives (AQS) and 2-deoxythymidine

2014 ◽  
Vol 06 (01) ◽  
pp. 1-4
Author(s):  
Jianhua Ma
Keyword(s):  
Triplet State ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Excited Triplet State ◽  
Time Resolved ◽  
Excited Triplet ◽  
Anthraquinone Derivatives

Oxygen sensing based on lifetime of photoexcited triplet state of platinum porphyrin-polystyrene film using time-resolved spectroscopy

2000 ◽  
Vol 04 (03) ◽  
pp. 292-299 ◽  
Author(s):  
YUTAKA AMAO ◽  
KEISUKE ASAI ◽  
ICHIRO OKURA
Keyword(s):  
Triplet State ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Oxygen Sensing ◽  
Laser Flash ◽  
Quenching Rate ◽  
Time Resolved ◽  
Quenching Rate Constant ◽  
Volmer Plot ◽  
Platinum Porphyrin

Optical oxygen-sensing systems based on the quenching of the photoexcited triplet state of platinum porphyrins—platinum octaethylporphyrin (PtOEP) and platinum tetrakis(pentafluorophenyl)porphyrin (PtTFPP)—in polystyrene (PS) using two different time-resolved spectroscopies (luminescence lifetime measurement and diffuse reflectance laser flash photolysis) have been developed. Using both spectroscopies, the same values of Stern-Volmer constant KSV and quenching rate constant kq (KSV = kqτ0) are obtained. The decays of the luminescence and triplet-triplet reflectance of the platinum porphyrins in PS consisted of two components (faster and slower lifetimes) in the absence and presence of oxygen. For both faster and slower components the lifetime decreases with increasing oxygen concentration. For both components a Stern-Volmer plot of the platinum porphyrin-PS films exhibits linearity. However, kq of the faster component is larger than that of the slower component (for PtOEP, three times larger; for PtTFPP, 40 times larger), indicating that two different oxygen-accessible sites exist in the platinum porphyrin-PS films. The faster and slower components are related to oxygen-accessible sites on the surface and in the bulk of the platinum porphyrin films respectively. Concerning the fractional contributions of each lifetime component, the contribution of the faster component is greater than that of the slower component, indicating that the sensing site on the surface is important for optical sensing. The contribution of different oxygen-accessible sites in platinum porphyrin-PS films for oxygen sensing is clarified by these techniques.

Exploratory study of the quenching of photosensitizers by initiators of free radical "living" polymerization

1997 ◽  
Vol 75 (1) ◽  
pp. 92-97 ◽  
Author(s):  
J.C. Scaiano ◽  
Terrence J. Connolly ◽  
Nadereh Mohtat ◽  
Claudette N. Pliva
Keyword(s):  
Free Radical ◽  
Exploratory Study ◽  
State Energy ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Time Resolved ◽  
Excited Triplet ◽  
Excited State Energy ◽  
Pyrene Fluorescence

Several compounds of the type PhCR1R2-TEMPO (where TEMPO = 2,2,6,6-tetramethylpiperidine-N-oxide) have been prepared and examined as potential photosensitized initiators for "living" free radical polymerizations. For example, these compounds are excellent quenchers of triplet xanthone (rate constants in the range (8.0–13) × 108 M−1 s−1) and result in the formation of benzylic and TEMPO radicals. The importance of excited state energy and nature of the excited triplet state have also been explored. We also tested pyrene as a possible singlet sensitizer. While pyrene fluorescence is efficiently quenched, the process does not lead to cleavage of the C—O bond. A model is proposed to account for this anomaly in the photosensitized decomposition of these TEMPO adducts. Keywords: TEMPO, laser flash photolysis, time resolved emission spectroscopy, sensitizers, quenching, photoinitiator.

The Excited Triplet State Properties of Titanyl Phthalocyanine and its Sulfonated Derivatives

2010 ◽  
Vol 63 (10) ◽  
pp. 1471 ◽  
Author(s):  
Xian-Fu Zhang ◽  
Jingyao Huang ◽  
Qian Xi ◽  
Yun Wang
Keyword(s):  
Aqueous Solution ◽  
Quantum Yield ◽  
Triplet State ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Zinc Phthalocyanine ◽  
Excited Triplet State ◽  
Nanosecond Laser ◽  
Excited Triplet ◽  
Titanyl Phthalocyanine

Titanyl phthalocyanine (TiOPc) is a well-known, excellent photoconductive material for laser printers and photocopying machines. Its organic derivatives have recently been shown to be excellent photosensitizers for singlet oxygen [O2(1Δg)] production. The excited triplet state properties of TiOPc, in homogeneous DMSO solution, were measured in this study for the first time by nanosecond laser flash photolysis. The data enabled comparisons to be drawn with TiOPcS4 and zinc phthalocyanine (ZnPc), ultimately providing a better understanding of the reported observations. Absorption, fluorescence, and O2(1Δg) sensitization were also studied. TiOPcS4 in DMSO shows remarkably different fluorescence properties from that reported in aqueous solution: both the fluorescence quantum yield (Φf = 0.068) and the fluorescence lifetime (τf = 3.71 ns) were much larger than that reported for aqueous solutions (0.012 and 0.09 ns, respectively). The photosensitizing properties of TiOPcS4 in DMSO are also so significantly better than that in aqueous solution, i.e. triplet lifetime (τT) of 252 μs, triplet quantum yield (ΦT) of 0.42, and the quantum yield of O2(1Δg) (ΦΔ) of 0.49; compare with values of 60 μs, 0.32, 0.13 reported in aqueous solution. TiOPc, however, shows comparable photophysical properties to that of ZnPc, a well-recognized photosensitizer. These results suggest that TiOPc and its derivatives are not only good photoconductors but also good photosensitizers of O2(1Δg), which may find application in photodynamic therapies for treatment of cancer.

Efficient photodecarboxylation of 3- and 4-acetylphenylacetic acids in aqueous solution

2004 ◽  
Vol 82 (12) ◽  
pp. 1760-1768 ◽  
Author(s):  
Lawrence A Huck ◽  
Musheng Xu ◽  
Kaya Forest ◽  
Peter Wan
Keyword(s):  
Aqueous Solution ◽  
Triplet State ◽  
Benzene Ring ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Excited Triplet ◽  
Acetophenone Derivatives ◽  
Acetyl Group ◽  
Electron Withdrawing Group

The photochemistry of 3- and 4-acetylphenylacetic acids (6 and 7) has been studied in aqueous solution. This work is a continuation of research efforts aimed at understanding the structural effects on the efficacy for benzyl carbanion photogeneration via photodecarboxylation. The nitro group (at the 3- and 4-positions) is known to be an exceptionally good activating group on the benzene ring — because of its enhanced electron-withdrawing effect in the excited triplet state — for photodecarboxylation and the related photo-retro-aldol type process. It is shown in this work that the acetyl group is an equally good activating group for the photodecarboxylation. Thus, the photochemistry of 6 and 7 parallels much of what was observed for the corresponding nitrophenylacetic acids 1 and 2. Both 6 and 7 photodecarboxylate efficiently (Φd = 0.60 and 0.22, respectively, at pH 7) via the carboxylate form, to give observable (by laser flash photolysis) benzyl carbanion or related intermediates. The meta isomer 6 displays an acid-catalyzed pathway for photodecarboxylation at pH < 3 and along with its enhanced overall reactivity, is consistent with a meta effect of the acetyl group. Triplet state reactivity is inferred from sensitization and laser flash photolysis experiments. Based on the results of this work, the acetyl group may now be viewed as an "enhanced" electron-withdrawing group (in the excited state) when attached to a benzene ring (i.e., in acetophenone derivatives) that is capable of inducing ionic reactions, which is not the traditional photochemistry that is expected from such compounds.Key words: photodecarboxylation, acid catalysis, acetophenone, photogenerated carbanion, enol, enolate.

Effect of Aggregation on Bacteriochlorin a Triplet-state Formation: A Laser Flash Photolysis Study¶

2002 ◽  
Vol 76 (5) ◽  
pp. 480 ◽  
Author(s):  
Xavier Damoiseau ◽  
Francis Tfibel ◽  
Maryse Hoebeke ◽  
Marie-Pierre Fontaine-Aupart
Keyword(s):  
Triplet State ◽  
State Formation ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash
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