Properties of singlet- and triplet-excited states of hemicyanine dyes

2014 ◽  
Vol 68 (8) ◽  
Author(s):  
Daniel Mártire ◽  
Walter Massad ◽  
Hernán Montejano ◽  
Mónica Gonzalez ◽  
Paula Caregnato ◽  
...  
Keyword(s):  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Fluorescence Emission ◽  
Emission Spectra ◽  
Laser Flash ◽  
Quantum Yields ◽  
Triplet States ◽  
Fluorescence Emission Spectra ◽  
Fluorescence Quantum Yields ◽  
Hemicyanine Dyes

AbstractThe fluorescence emission spectra and fluorescence quantum yields of hemicyanine dyes LDS 698, LDS 722, and LDS 730 were measured in different media. No transient species was detected in the laser flash-photolysis experiments performed with Ar-saturated solutions of the dyes in methanol. However, in the presence of 0.08 M potassium iodide, the absorption of the triplet states was clearly observed. Oxygen consumption measurements in the absence and presence of a chemical trap (furfuryl alcohol) in MeOH: H2O (φ r = 1: 1) solutions of the dyes containing KI confirmed the generation of singlet molecular oxygen.

scholarly journals Arylisoquinoline-derived organoboron dyes with a triaryl skeleton show dual fluorescence

2019 ◽  
Vol 15 ◽  
pp. 2612-2622
Author(s):  
Vânia F Pais ◽  
Tristan Neumann ◽  
Ignacio Vayá ◽  
M Consuelo Jiménez ◽  
Abel Ros ◽  
...  
Keyword(s):  
Emission Band ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Quantum Yields ◽  
Triplet States ◽  
Dual Emission ◽  
Long Wavelength ◽  
Fluorescence Quantum Yields ◽  
Wavelength Emission

Four new dyes that derive from borylated arylisoquinolines were prepared, containing a third aryl residue (naphthyl, 4-methoxynaphthyl, pyrenyl or anthryl) that is linked via an additional stereogenic axis. The triaryl cores were synthesized by Suzuki couplings and then transformed into boronic acid esters by employing an Ir(I)-catalyzed reaction. The chromophores show dual emission behavior, where the long-wavelength emission band can reach maxima close to 600 nm in polar solvents. The fluorescence quantum yields of the dyes are generally in the range of 0.2–0.4, reaching in some cases values as high as 0.5–0.6. Laser-flash photolysis provided evidence for the existence of excited triplet states. The dyes form fluoroboronate complexes with fluoride anions, leading to the observation of the quenching of the long-wavelength emission band and ratiometric response by the build-up of a hypsochromically shifted emission signal.

Photoexcitation and Electron Transfer Reactions of Zinc Lipidporphyrins in DMSO

1999 ◽  
Vol 03 (01) ◽  
pp. 53-59 ◽  
Author(s):  
TAKERU OHGUSHI ◽  
ZI-CHEN LI ◽  
FU-MIAN LI ◽  
TERUYUKI KOMATSU ◽  
SHINJI TAKEOKA ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Steric Effect ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Transfer Reactions ◽  
Quantum Yields ◽  
Electron Transfer Reactions ◽  
Fluorescence Quantum Yields ◽  
Photochemical Properties

The photophysical and photochemical properties of 5,10,15,20-tetrakis{α,α,α,α-o-[2′,2′-dimethyl-20′-((2″-(trimethylammonio)ethyl)phosphonatoxy)alkanamido]phenyl}porphinatozinc(II) (zinc lipidporphyrins, ZnLPs ( C 10, C 18)) have been studied in homogeneous DMSO solution and compared with those of 5,10,15,20-tetrakis{α,α,α,α-o-pivalamidophenyl}porphinatozinc(II) ( ZnTpivPP ) and tetrakis-phenylporphinatozinc(II) ( ZnTPP ). The fluorescence quantum yields of the ZnLPs were lower than that of ZnTPP , but their fluorescence lifetimes were relatively long. The electron transfer reactions from the photoexcited states of these Zn porphyrin complexes to several quinone derivatives were evaluated by fluorescence spectroscopy and laser flash photolysis. The efficiences of oxidative quenching of the excited porphyrins via a dynamic process were significantly decreased by the presence of the bulky substituents on one side of the porphyrin macrocycle. This steric effect of the porphyrin side-chains was quantitatively examined by the Marcus classical treatment.

Germanium triazatetrabenzcorrole and germanium phthalocyanine: Synthesis, fluorescence and singlet oxygen generation

2018 ◽  
Vol 22 (09n10) ◽  
pp. 847-852 ◽  
Author(s):  
Xian-Fu Zhang ◽  
Xiaojie Sun
Keyword(s):  
Singlet Oxygen ◽  
Fluorescence Emission ◽  
Emission Spectra ◽  
Fluorescence Properties ◽  
Quantum Yields ◽  
Fluorescence Lifetimes ◽  
Fluorescence Emission Spectra ◽  
Oxygen Generation ◽  
Fluorescence Quantum Yields ◽  
Singlet Oxygen Generation

The synthesis, fluorescence properties and singlet oxygen generation capability of germanium tetrabenzotriazacorrole (LGeTBC), germanium phthalocyanine (Cl[Formula: see text]GePc) and their derivatives are described. Measurements include UV-vis absorption spectra, fluorescence emission spectra, fluorescence quantum yields fluorescence lifetimes, and singlet delta oxygen quantum yields. LGeTBC and its derivatives exhibit quite different spectral and fluorescence properties from their phthalocyanine precursor. Both LGeTBC and Cl[Formula: see text]GePc show high singlet delta oxygen quantum yields and suitable fluorescence quantum yields, indicating that they can act as good singlet oxygen photosensitizers for photodynamic therapy.

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.

Kinetic study of the reactions of methoxy-substituted phenacyl radicals

1995 ◽  
Vol 73 (2) ◽  
pp. 223-231 ◽  
Author(s):  
S.V. Jovanovic ◽  
J. Renaud ◽  
A.B. Berinstain ◽  
J.C. Scaiano
Keyword(s):  
Rate Constant ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Chemical Reactivity ◽  
Laser Flash ◽  
Carbonyl Oxygen ◽  
Peroxyl Radicals ◽  
Quantum Yields ◽  
Triplet States ◽  
Singlet States

The photochemistry of various mono- and dimethoxy-substituted α-bromoacetophenones has been investigated by laser flash photolysis in organic solvents. The short-lived excited singlet states cleave to yield bromine atoms and the corresponding methoxyphenacyl radicals with quantum yields ranging from 0.13 to 0.35. With the exception of 4-methoxy-α-bromoacetophenone (6), all other substrates yield readily detectable triplet states; these have π,π* character and are very poor hydrogen abstractors. Triplet decay does not contribute to methoxyphenacyl radical formation. While methoxyphenacyl radicals may have a spin density as high as 0.3 at the carbonyl oxygen, which accounts for the alkoxy-like visible band in their absorption spectrum, their chemical reactivity is dominated by the radical character at the carbon site. Methoxyphenacyl radicals are modest hydrogen abstractors; for example, reaction of 6 with 1,4-cyclohexadiene occurs with a rate constant of 2.6 × 105 M−1 s−1, while for addition to the double bond in 1,1-diphenylethylene the rate constant is 9.4 × 107 M−1 s−1. Additions to other double bonds are likely to be slower (e.g., 12 + 1,3-cyclohexadiene, k ≤ 105 M−1 s−1). In contrast, reaction with oxygen occurs with kq = 2.5 × 109 M−1 s−1. Under the conditions relevant for their participation in paper yellowing, the methoxyphenacyl radicals will be converted to peroxyl radicals. These probably play a key role in the oxidative photodegradation of lignin. Keywords: methoxyphenacyl radicals, α-bromoacetophenones, laser flash photolysis.

Visible and Near-Infrared Fluorescence of Crude Oils

1995 ◽  
Vol 49 (6) ◽  
pp. 754-764 ◽  
Author(s):  
Taggart D. Downare ◽  
Oliver C. Mullins
Keyword(s):  
Energy Transfer ◽  
Near Infrared ◽  
Fluorescence Emission ◽  
Emission Spectra ◽  
Quantum Yields ◽  
Crude Oils ◽  
Excitation Wavelength ◽  
Fluorescence Emission Spectra ◽  
Fluorescence Quantum Yields ◽  
Oil Type

Fluorescence emission spectra and absolute quantum yields have been measured for ten diverse crude oils at various concentrations over a broad range of excitation and emission wavelengths in the visible and the near-infrared. Energy transfer produces large red shifts and large widths in the fluorescence emission spectra for shorter wavelength excitation particularly for heavier crude oils. However, the effects of energy transfer are nearly absent for near-infrared excitation; all crude oils exhibit nearly the same emission spectra for long wavelength excitation. In addition, the fraction of emission resulting from collisional energy transfer relative to nascent emission is almost independent of oil type; it is governed by quantum yield characteristics. Absolute fluorescence quantum yields of ten crude oils (and three rhodamine dyes for validation) were measured with respect to scattering of latex microspheres in distilled water. Fluorescence quantum yields vary systematically with crude oil type as well as excitation wavelength; quantum yields are lower for high fluorophore concentrations (heavy crude oils) and for longer wavelength excitation. Stern-Volmer analyses of the quantum yields indicate that simple models apply and show the relative quenching rates for different excitation wavelengths.

Laser flash photolysis studies of the formation and reactivities of phenyl(naphthyl)methyl carbocations generated from phosphonium salt precursors

1992 ◽  
Vol 70 (6) ◽  
pp. 1784-1794 ◽  
Author(s):  
E. O. Alonso ◽  
L. J. Johnston ◽  
J. C. Scaiano ◽  
V. G. Toscano
Keyword(s):  
Rate Constants ◽  
Phosphonium Salt ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Ion Pairs ◽  
Laser Flash ◽  
Product Formation ◽  
Quantum Yields ◽  
Back Reaction ◽  
Transient Experiments

The photolysis of several substituted phenyl(naphthyl)methyl triphenylphosphonium chlorides has been examined using a combination of laser flash photolysis experiments and product studies. Both carbocation and radical intermediates have been characterized in the transient experiments, with the relative yields depending strongly on the solvent. For example, in alcohols, acetonitrile, or aqueous solvents cation formation predominates while acetonitrile/dioxane mixtures (5–10%) are required for the observation of radicals. Quantum yields for cation formation vary from 0.79 in methanol to 0.093 in 1:4 acetonitrile/dioxane, as measured by product studies and transient experiments, respectively. The addition of perchlorate salts leads to dramatic enhancements in the cation lifetimes; the effects are particularly pronounced for acetonitrile/dioxane mixtures where the cation yields also increase by factors of 3–4. In this case the effects are attributed primarily to replacement of chloride by perchlorate in the initial ion pairs. The combined data from both solvent and perchlorate salt effects on the cation lifetimes and yields suggest that the excited state of the phosphonium salt cleaves homolytically, followed by electron transfer within the initial radical/triphenylphosphine radical cation pair to generate carbocation, as opposed to direct heterolytic cleavage. The cation yields also indicate that back reaction to regenerate starting material, as well as product formation within the initial geminate cage, occur in some solvents. The effects of solvent and added perchlorate salts on the rate constants for reaction with nucleophiles have been examined. For example, rate constants that vary by an order of magnitude have been measured for quenching by azide ion in various aqueous acetonitrile and trifluoroethanol mixtures.

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