Laser flash photolysis studies of some rhodamine dyes Characterisation of the lowest excited singlet state of Rhodamine 3B, Sulforhodamine B and Sulforhodamine 101

1998 ◽  
Vol 94 (2) ◽  
pp. 195-199 ◽  
Author(s):  
Paul C. Beaumont ◽  
David G. Johnson ◽  
Barry J. Parsons
Keyword(s):  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Singlet State ◽  
Laser Flash ◽  
Excited Singlet State ◽  
Excited Singlet ◽  
Sulforhodamine B ◽  
Sulforhodamine 101 ◽  
Rhodamine Dyes

Steady state and time-resolved spectroscopic studies of the photochemistry of 1-arylsilacyclobutanes and the chemistry of 1-arylsilenes

1999 ◽  
Vol 77 (5-6) ◽  
pp. 1136-1147 ◽  
Author(s):  
William J Leigh ◽  
Rabah Boukherroub ◽  
Christine J Bradaric ◽  
Christine C Cserti ◽  
Jennifer M Schmeisser
Keyword(s):  
Rate Constants ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Singlet State ◽  
Fluorescence Emission ◽  
Laser Flash ◽  
Excited Singlet State ◽  
Acetonitrile Solution ◽  
Quantum Yields ◽  
Excited Singlet

Direct photolysis of 1-phenylsilacyclobutane and 1-phenyl-, 1-(2-phenylethynyl)-, and 1-(4'-biphenylyl)-1-methylsilacyclobutane in hexane solution leads to the formation of ethylene and the corresponding 1-arylsilenes, which have been trapped by photolysis in the presence of methanol. Quantum yields for photolysis of the three methyl-substituted compounds have been determined to be 0.04, 0.26, and 0.29, respectively, using the photolysis of 1,1-diphenylsilacyclobutane Φsilene = 0.21) as the actinometer. The corresponding silenes have been detected by laser flash photolysis; they have lifetimes of several microseconds, exhibit UV absorption maxima ranging from 315 to 330 nm, and react with methanol with rate constants on the order of (2-5) × 109 M-1 s-1 in hexane. Absolute rate constants for reaction of 1-phenylsilene and 1-methyl-1-phenylsilene with water, methanol, tert-butanol, and acetic acid in acetonitrile solution have been determined, and are compared to those of 1,1-diphenylsilene under the same conditions. With the phenylethynyl- and biphenyl-substituted methylsilacyclobutanes, the triplet states can also be detected by laser flash photolysis, and are shown to not be involved in silene formation on the basis of triplet sensitization and (or) quenching experiments. Fluorescence emission spectra and singlet lifetimes have been determined for the three 1-aryl-1-methylsilacyclobutanes, 1,1-diphenylsilacyclobutane, and a series of acyclic arylmethylsilane model compounds. These data, along with the reaction quantum yields, allow estimates to be made of the rate constants for the excited singlet state reaction responsible for silene formation. 1-Methyl-1-phenylsilacyclobutane undergoes reaction from its lowest excited singlet state with a rate constant 10-80 times lower than those of the other three derivatives. The results are consistent with a stepwise mechanism for silene formation, involving a 1,4-biradicaloid intermediate that partitions between product and starting material.Key words: silene, silacyclobutane, photochemistry, biradical.

Cyclobutene photochemistry. Substituent effects on the photochemistry of 1-phenylcyclobutene

1995 ◽  
Vol 73 (2) ◽  
pp. 191-203 ◽  
Author(s):  
William J. Leigh ◽  
J. Alberto Postigo
Keyword(s):  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Singlet State ◽  
Substituent Effects ◽  
Methanol Solution ◽  
Excited Singlet State ◽  
Acetonitrile Solution ◽  
Quantum Yields ◽  
Nanosecond Laser ◽  
Excited Singlet

The photochemistry and photophysics of 1-phenylcyclobutene and five aryl-substituted derivatives have been studied in various solvents at room temperature. All six compounds fluoresce with quantum yields in the 0.2–0.3 range in cyclohexane and acetonitrile solution. 1-Phenylcyclobutene undergoes [2+2]-cycloreversion [Formula: see text] to yield phenylacetylene upon photolysis in either hydrocarbon or acetonitrile solution, and undergoes (Markovnikov) solvent addition upon irradiation in methanol solution [Formula: see text] in addition to cycloreversion. Triplet sensitization and quenching experiments indicate that cycloreversion and methanol addition are both excited singlet state processes. None of the six compounds studied undergo ring opening to the corresponding 2-aryl-1,3-butadiene in detectable yield. Quantum yields for cycloreversion in cyclohexane, acetonitrile, and methanol solution and methanol addition have been determined for the six compounds, along with excited singlet state lifetimes. The quantum yields and rate constants for cycloreversion and methanol addition are both enhanced by substitution with electron-donating groups. The variation in the rate constant for [2+2]-cycloreversion with substituent indicates that there is substantial dipolar character developed in the cyclobutenyl σ-bond framework during the reaction, in almost exact correspondence with that developed in the π system during photoprotonation. No deuterium scrambling is observed in 1-phenylcyclobutene-2,4,4-d3 after photolysis in pentane solution to ca. 80% conversion, indicating that skeletal rearrangements leading to cyclopropyl carbenes do not occur in the direct photolysis of arylcyclobutene derivatives. A pericyclic mechanism for the photocycloreversion reaction is suggested. Triplet–triplet absorption spectra and triplet lifetimes of 1-phenyl-, 1-(para-methylphenyl)-, and 1-(para-trifluoromethylphenyl)cyclobutene in hydrocarbon solution are also reported. Keywords: photochemistry, cyclobutene, fluorescence, [2+2]-cycloreversion, substituent effects, nanosecond laser flash photolysis, lifetime, triplet state, styrene, photoaddition

Enhanced basicity of 1,3-dialkoxy-substituted benzenes: cyclophane derivatives

1994 ◽  
Vol 72 (12) ◽  
pp. 2388-2395 ◽  
Author(s):  
Guangzhong Zhang ◽  
Yijian Shi ◽  
Renée Mosi ◽  
Thao Ho ◽  
Peter Wan
Keyword(s):  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Structural Constraints ◽  
Excited Singlet ◽  
Deuterium Incorporation ◽  
Stable Conformation ◽  
Substituted Benzenes ◽  
Singlet States ◽  
Excited Singlet States

The photoprotonation of four dialkoxy-substituted benzenes in their excited singlet states has been studied. The parent systems 4 and 5 are regioselectively photoprotonated at the 2-position, with significant quantum efficiencies for deuterium incorporation at acidities greater than pH 2. The structurally related cyclophane derivatives 6 and 7 did not show any deuterium exchange over the same acidity range but fluorescence quenching by proton (in aqueous solution) and laser flash photolysis studies (in 1,1,1,3,3,3-hexafluoro-2-propanol) indicate that photoprotonation does take place with these compounds. Due to structural constraints imposed by the most stable conformation adopted by these molecules (6 and 7), the attacking proton (deuteron) is also the proton (deuteron) that is deprotonated from the cyclohexadienyl cation (2,6-dialkoxybenzenonium ion) intermediate, resulting in the absence of incorporation of deuterium.

Studies of triplet chlorophyll by microbeam flash photolysis

1966 ◽  
Vol 295 (1440) ◽  
pp. 1-12 ◽  
Keyword(s):  
Half Life ◽  
Room Temperature ◽  
Flash Photolysis ◽  
Singlet State ◽  
Excited Singlet State ◽  
Intermolecular Distance ◽  
Plant Leaves ◽  
Excited Singlet ◽  
Cationic Detergent ◽  
Photolysis Apparatus

A microbeam flash photolysis apparatus has been developed for use with samples 50 to 250 μ m square, and from 5 to several hundred microns thick. Triplets of chlorophyll a and b were observed in a number of solid solvents, including cholesterol, at room temperature without prior outgassing. In cholesterol the triplet yield decreased with increasing concentration according to the Stern-Volmer law, but the half life of the chlorophyll b triplet was 3 ± 0.2 ms, and independent of concentration. Therefore, the excited singlet state but not the triplet is quenched by a concentration-dependent process. The half-quenching concentration of 2 x 10 -3 M, corresponding to a mean intermolecular distance of 95 Å, points to quenching by inductive resonance. No triplets of chlorophyll appeared on flashing normal or etiolated plant leaves. Leaves treated with cationic detergent gave triplets in a yield of 15%, and exhibited increased fluorescence.

Photodegradation of the lignin model α-guaiacoxyacetoveratrone, unusual effects of solvent, oxygen, and singlet state participation

1991 ◽  
Vol 69 (1) ◽  
pp. 104-107 ◽  
Author(s):  
John A. Schmidt ◽  
Alain B. Berinstain ◽  
Francis de Rege ◽  
Cyril Heitner ◽  
Linda J. Johnston ◽  
...  
Keyword(s):  
Model Compound ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Singlet State ◽  
Laser Flash ◽  
Quantum Yields ◽  
Aprotic Solvents ◽  
Lignin Model Compound ◽  
State Participation ◽  
Lignin Model

α-Guaiacoxyacetoveratrone, a lignin model compound, has been studied using a combination of laser flash photolysis and steady state quantum yields. Triplet lifetimes range from 175 to 600 ns while the quantum yields of photodegradation vary from 0.06 to 0.6, depending on the solvent. Singlet processes (Φ ~ 0.1), previously unobserved for aromatic ketones, are implicated in the mechanism, and account for most or all of the degradation in aprotic solvents. Key words: photodegradation, α-guaiacoxyacetoveratrone.

Trans to cis photoisomerization of N,N′-disubstituted indigo dyes via excited singlet states; a laser flash photolysis and steady state irradiation study

1987 ◽  
Vol 65 (4) ◽  
pp. 708-717 ◽  
Author(s):  
Helmut Görner ◽  
Joseph Pouliquen ◽  
Jean Kossanyi
Keyword(s):  
Steady State ◽  
Triplet State ◽  
Room Temperature ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Excited Singlet ◽  
Triplet Energy ◽  
Direct Excitation ◽  
Indigo Dyes

The relaxation pathways of excited trans-N,N′-diacylindigo dyes (trans-1–trans-4) and of the rigid trans (5) and cis (6) indigo analogues have been studied by nanosecond flash photolysis and steady state measurements. In fluid solution the trans to cis photoisomerization of 1–4 occurs via a singlet excited state mechanism on direct excitation, and the triplet state appears to be reached only by sensitized reaction. The lower quantum yield for trans → cis isomerization of 2–4 at room temperature, as compared to 1, is due to a thermally activated internal conversion step leading to the trans ground state. This pathway competes with fluorescence and twisting of the molecule around the central double bond in the excited singlet state. Increasing the viscosity of the medium decreases the twisting of the flexible molecules and, as a consequence, increases the population of the lowest triplet state. A triplet transient, the intensity of which increases with the viscosity of the medium, could be characterized at low temperature under direct excitation. A transient species, which can be assigned to a triplet state on the basis of quenching experiments and on the fact that the same transient could be found under sensitized conditions, also has been observed at room temperature for the rigid 5 and 6 molecules. Quenching measurements of triplet sensitizers by 5, trans-1, and trans-2 enables the localization of the triplet energy at around 40 kcal/mol.

Primary Photochemical Processes of the Phototoxic Neuroleptic Cyamemazine: A Study by Laser Flash Photolysis and Steady State Irradiation

2004 ◽  
Author(s):  
Patrice Morlière ◽  
Francisco Bosca ◽  
Miguel Miranda ◽  
José Castell ◽  
René Santus
Keyword(s):  
Steady State ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Photochemical Processes

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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