scholarly journals Kinetics and Mechanism of the Photochromism of N-Phenyl-Rhodaminelactame

1989 ◽  
Vol 10 (2) ◽  
pp. 63-72 ◽  
Author(s):  
H. Willwohl ◽  
J. Wolfrum ◽  
R. Gleiter
Keyword(s):  
Quantum Yield ◽  
Picosecond Laser ◽  
Laser Pulses ◽  
Laser Flash ◽  
Time Resolved ◽  
First Order ◽  
First Order Kinetics ◽  
Relative Quantum ◽  
Millisecond Time Scale ◽  
Resolution Single

The photochromism of N-phenyl-rhodaminelactame (3' ,6' -bis-(diethylamino)-2-phenyl-spiro[1H-isoindole-1,9'[9H] Xanthaen]-3-[2H]-one) was investigated in solutions of acetonitrile, dioxane and mixtures of dioxane with H20, methanol and ethanol by laser flash time resolved absorption measurements. The colouring reaction kinetics and the relative quantum yield of the red product were measured using nanosecond excimer laser excitation at 308 nm. In most cases, first order kinetics was.observed. The first order rate constants and the quantum yield were found to be dependent on the solvent and the number of laser pulses that had previously irradiated the solution. The thermal fading reaction occurred on a millisecond timescale and showed large deviations from first order kinetics in all solvents. In addition, picosecond laser pulses at 285 nm were used to measure the fluorescence lifetime of the S1 state of the rhodamine derivative with picosecond resolution. Single exponential decays were observed in all solvents and the lifetime ranged between 3 and 6 nanoseconds. We conclude that the photoreaction does not proceed directly from the S1 state, and propose a mechanism for the photochromic process, in which an intermediate decomposes to rotameric isomers of the coloured product, which are not equilibrated on the millisecond time scale of the reverse reaction.

Optical Limiting With Neutral Nickel Dithiolene Complexes

1999 ◽  
Vol 597 ◽  
Author(s):  
W. L. Tan ◽  
W. Ji ◽  
J. L. Zuo ◽  
J. F. Bai ◽  
X. Z. You ◽  
...  
Keyword(s):  
Benzene Solution ◽  
Excited State Absorption ◽  
Picosecond Laser ◽  
Laser Pulses ◽  
Optical Limiting ◽  
Linear Absorption ◽  
Time Resolved ◽  
Pump Probe ◽  
Limiting Behavior ◽  
Picosecond Pulses

AbstractWe report an investigation of optical-limiting behavior in two neutral nickel complexes with multi-sulfur 1,2 dithiolene ligands, [Ni(medt)2] I (medt = 5,6-dihydro-6-methyl-1,4-dithiin-2,3- dithiolate) and [Ni(phdt)2] 2 (phdt = 5,6-dihydro-5-phenyl-l,4-dithiin-2,3-dithiolate) in benzene solution. The fluence-dependent transmission of the complexes was observed with nanosecond and picosecond laser pulses at 532-nm wavelength. The limiting thresholds of the complexes were ˜0.3 J/cm2, when measured with the picosecond pulses. Both picosecond time-resolved pump-probe and Z-scan measurement revealed that the limiting effects should originate from excited-state absorption and refraction. The transparency window (400˜900 nm), observed in the linear absorption spectra of the complexes, indicated that their limiting response should cover a wider range than those of fullerenes and phthalocyanines.

Photoluminescence of Eu3+ in Si/SiO2 Nanostructure Films

2000 ◽  
Vol 609 ◽  
Author(s):  
Huimin Liu ◽  
Aziz Mahfoud ◽  
G. A. Nery ◽  
O. Resto ◽  
Luis F. Fonseca ◽  
...  
Keyword(s):  
Energy Transfer ◽  
Life Time ◽  
Picosecond Laser ◽  
Laser Pulses ◽  
Photon Absorption ◽  
Intense Laser ◽  
Time Resolved ◽  
Silicon Matrix ◽  
Sputtering Deposition ◽  
Direct Excitation

ABSTRACTEu3+ -doped Si/SiO2 nanocomposites were successfully prepared by Ar sputtering deposition on quartz substrates. The optical properties were studied using time-resolved photoluminescence spectroscopy. Excited by intense picosecond laser pulses with energy greater than1GW/cm2 and wavelength at 532nm the observed photoluminescence consists of a rapidly decaying component with life time of ∼1 s and a slowly component with life time of ∼ 2 ms. The former was recognized as coming from Si/SiO2 nanostructures matrix while the latter as coming from the impurity Eu3+ ions. Using the intense laser excitation a two-photon absorption by silicon matrix occurred, resulting in photo-induced carriers produced in conduction band. A direct recombination from Si/SiO2 nanostructure host gives a weak but fast emission, and creates a large number of nonequilibrium phonon. For Eu3+ emission a set of 5D0 to 7F multiplet transitions were identified. In addition to the direct excitation by 532nm the excited state 5D0 of Eu3+ ions was also found to be populated due to energy transfer from silicon matrix. The mechanism of phonon-assisted energy transfer is discussed.

Substituted Phosphorous Triazatetrabenzocorroles: Correlation Between Structure and Excited State Properties

2009 ◽  
Vol 62 (5) ◽  
pp. 434 ◽  
Author(s):  
Xian-Fu Zhang ◽  
Yakuan Chang ◽  
Yanling Peng ◽  
Fushi Zhang
Keyword(s):  
Quantum Yield ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Photophysical Properties ◽  
Laser Flash ◽  
Time Resolved Fluorescence ◽  
Absorption Properties ◽  
Strong Electron ◽  
Time Resolved ◽  
Triplet Formation

The photophysical properties of five novel phthalocyanine analogues, dihydroxy phosphorus(v) triazatetrabenzocorrole (PTBC) substituted with –NO2, –SO3H, OiPr, and –NH2, respectively, were studied by a combination of absorption, steady-state emission, time-resolved fluorescence, and laser flash photolysis. All substituents, even for the strong electron-donating –NH2, cause only a slight red shift of their absorption and emission maxima. These complexes are generally monomeric in organic solution, whereas the sulfonated derivative, PTBC(SO3H)4, slightly aggregates in aqueous buffer. Distinct from phthalocyanines, PTBCs substituted with –NO2 or –NH2 still show high photo activities. The electron-withdrawing –NO2 and –SO3H decrease the fluorescence quantum yield but increase the triplet formation yield to 0.76 and 0.82, respectively. All PTBCs have long triplet lifetimes and hence generate singlet oxygen efficiently with a quantum yield from 0.43 to 0.75. Together with the ground-state absorption properties, the results suggest that these PTBCs may be used as excellent photosensitizers for photodynamic therapy.

scholarly journals Alanine Formation in Aqueous Solution of Ammonium Acrylate Induced by UV Picosecond Laser Pulses

1988 ◽  
Vol 8 (1) ◽  
pp. 13-17
Author(s):  
E. V. Khoroshilova ◽  
N. P. Kuzmina ◽  
Yu. A. Matveetz
Keyword(s):  
Aqueous Solution ◽  
Amino Acids ◽  
Quantum Yield ◽  
Laser Intensity ◽  
Electronic States ◽  
Picosecond Laser ◽  
Laser Pulses ◽  
Intensity Dependence ◽  
Picosecond Laser Pulses ◽  
Nonlinear Character

Formation of amino acids (α- and β-alanine) and oligomers containing NH2-groups, have been discovered under the irradiation of aqueous solution of ammonium acrylate by picosecond laser pulses with intensity up to 1 GW/cm2, λ = 266 nm.The composition of photoproducts was shown to depend on intensity of laser pulses. The laser intensity dependence of the β-alanine quantum yield was of a nonlinear character. The β-alanine formation occurred under the excitation of highly singlet electronic states of ammonium acrylate molecule by two quanta of UV or one quantum of VUV light. The unimolecular mechanism of amino acid formation in such a reaction was suggested.

Far-UV laser flash photolysis in solution. A time-resolved spectroscopic study of the chemistry of 1,1-dimethyl-1,3-(1-sila)-butadiene

1997 ◽  
Vol 75 (7) ◽  
pp. 975-982 ◽  
Author(s):  
Corinna Kerst ◽  
Martin Byloos ◽  
William J. Leigh
Keyword(s):  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Activation Parameters ◽  
Laser Flash ◽  
Ring Closure ◽  
Time Resolved ◽  
Decay Rate Constant ◽  
Hydrocarbon Solvents ◽  
First Order Kinetics ◽  
193 Nm

Laser flash photolysis (193 nm) of 1,1-dimethyl-(1-sila)cyclobut-2-ene in hexane solution leads to the formation of a transient species [Formula: see text] assigned to 1,1-dimethyl-1,3-(1-sila)butadiene on the basis of its UV absorption spectrum (λmax = 312 nm), and reactivity toward methanol (kMeOH = (3.6 ± 0.1) × 109 M−1 s−1; kH/kD = 1.3 ± 0.1), ethanol (kEtOH = (2.41 ± 0.06) × 109 M−1 s−1), tert-butanol (kBuOH = (1.8 ± 0.1) × 109 M−1 s−1; kH/kD = 1.5 ± 0.1), and oxygen [Formula: see text]. Experiments using isooctane and acetonitrile as solvent are also described. In acetonitrile, the lifetime of the silene is shortened considerably compared to hydrocarbon solvents, presumably due to quenching by adventitious water. In isooctane, under conditions of low excitation intensity, the siladiene decays with clean pseudo-first-order kinetics and a maximum lifetime of ~ 5 μs at 23 °C. The decay rate constant varies only slightly with temperature over the 20–60 °C range, leading to Arrhenius activation parameters of Ea = 0.5 ± 0.2 kcal/mol and log A = 5.7 ± 0.2. While steady state irradiation experiments suggest that in the absence of silene traps the predominant fate of the silabutadiene is thermal ring closure to regenerate the precursor, it is concluded that the rate constants and activation parameters for decay of the siladiene measured by flash photolysis represent a composite of those due to thermal electrocyclic ring closure (with Ea > ~3 kcal/mol) and reaction with adventitious quenchers (probably water, with Ea < 0). The measured Arrhenius parameters for reaction of the siladiene with methanol in isooctane (Ea = −2.6 ± 0.3 kcal/mol and log A = 7.6 ± 0.3) are consistent with this proposal. The potential and limitations of the use of 193-nm laser excitation for flash photolysis studies in solution are discussed. Keywords: far-UV, silene, flash photolysis, kinetics, electrocyclic.

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