scholarly journals A comparative study of the photochemistry of biphenyl adsorbed on cellulose and silicalite

2004 ◽  
Vol 6 (4) ◽  
pp. 193-198 ◽  
Author(s):  
J. P. Da Silva ◽  
L. F. Vieira Ferreira
Keyword(s):  
Ground State ◽  
Diffuse Reflectance ◽  
Solid Support ◽  
Ground State Absorption ◽  
Solid Supports ◽  
Time Resolved ◽  
Planar Configuration ◽  
Degradation Analysis ◽  
Photochemical Behaviour ◽  
Product Degradation

The photochemistry of biphenyl (BP) was studied on two model solid supports, silicalite and cellulose, using time resolved diffuse reflectance techniques and product degradation analysis. The results showed that the photochemical behaviour of BP depends on the solid support. Ground state absorption spectra indicated a near planar configuration in the ground state. BP triplet state was the only species detected on cellulose, while the radical cation(BP•+)was observed in silicalite. BP is relatively stable in both supports. Prolonged irradiations in cellulose lead to the formation of the three monohydroxybiphenyls, while in silicalite photooxidation products prevailed.

An Introduction to Time-Resolved Pump/Probe Spectroscopy

1985 ◽  
Vol 39 (3) ◽  
pp. 444-451 ◽  
Author(s):  
F. E. Lytle ◽  
R. M. Parrish ◽  
W. T. Barnes
Keyword(s):  
Absorption Spectra ◽  
Ground State ◽  
Fluorescence Spectra ◽  
Excited State Absorption ◽  
Time Dependent ◽  
Triplet Excited State ◽  
Ground State Absorption ◽  
Time Resolved ◽  
Pump Probe ◽  
Probe Spectroscopy

The construction and operating principles of a two-color pump/probe spectrometer are described. This instrument is capable of obtaining ground-state absorption spectra, both singlet-singlet and triplet-triplet excited-state absorption spectra, photoproduct spectra, and stimulated fluorescence spectra. In addition, time-dependent measurements can be made with an impulse response of 250 ps and a free temporal range of 13 ns.

scholarly journals Surface photochemistry: Photodegradation study of pyrene adsorbed onto microcrystalline cellulose and silica

2004 ◽  
Vol 6 (4) ◽  
pp. 205-213 ◽  
Author(s):  
A. S. Oliveira ◽  
L. F. Vieira Ferreira ◽  
J. P. Da Silva ◽  
J. C. Moreira
Keyword(s):  
Radical Cation ◽  
Microcrystalline Cellulose ◽  
Ground State ◽  
Diffuse Reflectance ◽  
Transient Absorption ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Cation Radical ◽  
Laser Flash ◽  
Time Resolved

Ground-state diffuse reflectance, time resolved laser-induced luminescence, diffuse reflectance laser flash-photolysis transient absorption and chromatographic techniques were used to elucidate the photodegradation processes of pyrene adsorbed onto microcrystalline cellulose and silica. Ground-state diffuse reflectance showed that on both substrates low concentrations display absorption of pyrene monomers. At high concentrations spectral changes attributed to aggregate formation were observed. Laser induced fluorescence showed that pyrene onto microcrystalline cellulose mainly presents fluorescence from monomers, while for silica, excimer-like emission was observed from low surface loadings (≥0.5μmolg−1). Transient absorption and photodegradation studies were performed at concentrations where mainly monomers exist. On silica, pyrene presents transient absorption from its radical cation. On microcrystalline cellulose both radical cation, radical anion and pyrene triplet-triplet absorption were detected. Irradiation followed by chromatographic analysis showed that pyrene decomposes on both substrates. For pyrene on microcrystalline cellulose 1-hydroxypyrene was the main identified photoproduct since in the absence of oxygen further oxidation of 1-hydroxypyrene was very slow. For pyrene on silica photodegradation was very efficient. Almost no 1-hydroxypyrene was detected since in the presence of oxygen it is quickly oxidized to other photooxidation products. On both substrates, pyrene radical cation is the intermediate leading to photoproducts and oxygen it is not involved in its formation.

scholarly journals Time-Resolved Investigation of the Molecular Chemiluminescence SrI(A2∏1/2,3,2,B2∑+→X2∑+) and the Atomic Resonance Fluorescence Sr(53P1→51S0) Following The Pulsed Dye Laser Generation Of Sr(53PJ) in the Presence of CF3I

1995 ◽  
Vol 16 (2) ◽  
pp. 121-138 ◽  
Author(s):  
S. Antrobus ◽  
D. Husain ◽  
Jie Lei ◽  
F. Castaño ◽  
M. N. Sanchez Rayo
Keyword(s):  
Ground State ◽  
Branching Ratio ◽  
Atomic Emission ◽  
Electronic Energy ◽  
Dye Laser ◽  
Pulsed Dye Laser ◽  
Laser Generation ◽  
Buffer Gas ◽  
Resonance Fluorescence ◽  
Time Resolved

A time-resolved investigation is presented of the electronic energy distribution in SrI following the collision of the optically metastable strontium atom, Sr [5s5p(3PJ)], with the molecule CF3I. Sr[5s5p(3PJ)], 1.807 eV above its 5s2(1S0) electronic ground state, was generated by pulsed dye-laser excitation of ground state strontium vapour to the Sr(53P1) state at , λ =689.3 nm {Sr(53P1←51S0)} at elevated temperature (840 K) in the presence of excess helium buffer gas in which rapid Boltzmann equilibration within the 53PJ spin-orbit manifold takes place. Time resolved atomic emission from Sr(53P1→51S0) at the resonance transition and the molecular chemiluminescence from SrI(A2∏1,2,3/2,B2∑+→X2∑+) resulting from reaction of the excited atom with CF3I were recorded and shown to be exponential in character. SrI in the A2∏1/2,3/2 (172.5, 175.4 kJ mol-1) and B2∑+ (177.3 kJ mol-1) states are energetically accessible on collision by direct-I-atomic abstraction between Sr(3P) and CF3I. The first-order decay coefficients for the atomic and molecular emissions are found to be equal under identical conditions and hence SrI(A2∏1/2,3/2, B2∑+) are shown to arise from direct I- atom abstraction reactions. The molecular systems recorded were SrI (A2∏1/2→X2∑+, Δv=0, λ=694 nm), SrI(A2∏3/2→X2∑+, Δv=0, λ=677 nm) and SrI(B2∑+→X2∑+) (Δv=0, λ=674 nm), dominated by the Δv=0 sequences on account of Franck-Condon considerations. The combination of integrated m61ecular and atomic intensity measurements yields estimates of the branching ratios into the specific electronic states, A1/2, A3/2 and B, arising from Sr(53PJ)+CF3I which are found to be as follows: A1/2,1.2 × 10-2; A3/2, 6.7 × 10-3; B, 5.1 × 10-3 yielding ∑SrI(A1/2+A3/2+B)=2.4 × 10-2. As only the X, A and B states SrI are accessible on reaction, assuming that the removal of Sr(53PJ) occurs totally by chemical removal, this yields an upper limit for the branching ratio into the ground state of ca. 98%. The present results are compared with previous time-resolved measurements on excited states of strontium halides that we have reported on various halogenated species resulting from reactions of Sr(53PJ), together with analogous chemiluminescence studies on Sr(3PJ) and Ca(43PJ) from molecular beam measurements.

Increasing the triplet lifetime and extending the ground-state absorption of biscyclometalated Ir(iii) complexes for reverse saturable absorption and photodynamic therapy applications

2016 ◽  
Vol 45 (41) ◽  
pp. 16366-16378 ◽  
Author(s):  
Chengzhe Wang ◽  
Levi Lystrom ◽  
Huimin Yin ◽  
Marc Hetu ◽  
Svetlana Kilina ◽  
...  
Keyword(s):  
Photodynamic Therapy ◽  
Ground State ◽  
Saturable Absorption ◽  
Reverse Saturable Absorption ◽  
Ground State Absorption ◽  
Saturable Absorbers ◽  
Triplet Lifetime

Tuning the photophysics of cationic Ir(iii) complexes via π-expansive ligands dramatically impacts their applications as broadband reverse saturable absorbers and in photodynamic therapy and theranostics.

scholarly journals Fluorescent chemosensors for metal ions based on 3-(2-benzoxazol-5-yl)alanine skeleton

2010 ◽  
Vol 8 (3) ◽  
pp. 674-686 ◽  
Author(s):  
Magda Milewska ◽  
Katarzyna Guzow ◽  
Wiesław Wiczk
Keyword(s):  
Steady State ◽  
Fluorescence Spectroscopy ◽  
Metal Ions ◽  
Ground State ◽  
Transition Metal Ions ◽  
Fluorescent Chemosensors ◽  
Time Resolved Fluorescence ◽  
Absorption Bands ◽  
Time Resolved ◽  
Ratiometric Sensors

AbstractThe ability of new chelate ligands, benzoxazol-5-yl-alanine derivatives substituted in position 2 by heteroaromatic substituent, to form complexes with selected metal ions in acetonitrile are studied by means of absorption and steady-state and time-resolved fluorescence spectroscopy. Among the ligands studied, only azaaromatic derivatives form stable complexes with transition metal ions in the ground state. Their absorption bands are bathochromically shifted enabling to use those ligands as ratiometric sensors. The fluorescence of each ligand is quenched by metal ions, however, in the presence of Cd(II) and Zn(II) ions a new red shifted emission band is observed.

scholarly journals Structural dynamics of the Ca2+-ATPase studied by time-resolved infrared spectroscopy

2008 ◽  
Vol 22 (2-3) ◽  
pp. 63-82 ◽  
Author(s):  
Andreas Barth
Keyword(s):  
Infrared Spectroscopy ◽  
Structural Dynamics ◽  
Ground State ◽  
Transfer Reaction ◽  
High Reactivity ◽  
Acetyl Phosphate ◽  
Time Resolved ◽  
Closed Conformation ◽  
Sarcoplasmic Reticulum Membrane ◽  
Time Resolved Infrared Spectroscopy

This review discusses the contribution of time-resolved infrared spectroscopy to the understanding of the Ca2+pump in the sarcoplasmic reticulum membrane of skeletal muscle cells (SERCA1a). The focus is on interactions of the substrate ATP with the ATPase and on the bond parameters of the phosphoenzyme phosphate group. Functional groups throughout the ATP molecule are important for stabilising the closed conformation of the ATP–ATPase complex and for fast phosphorylation of the ATPase. Dissociation of the reaction product ADP after phosphorylation leads to a more open average conformation of the enzyme and does not trigger the transition from the first phosphoenzyme Ca2E1P to the second E2P. The P–O bond between phosphate and aspartyl moieties is weaker in Ca2E1P and E2P than in acetyl phosphate in aqueous solution, which explains the high reactivity of the phosphoenzymes. This ground state property of the phosphoenzymes prepares for a phosphate transfer reaction with dissociative character.

scholarly journals Спиновая динамика отрицательно заряженных экситонов в квантовых точках InP/(In,Ga)P в магнитном поле

2020 ◽  
Vol 62 (11) ◽  
pp. 1816
Author(s):  
С.В. Некрасов ◽  
Ю.Г. Кусраев ◽  
И.А. Акимов ◽  
L. Langer ◽  
M. Kotur ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Quantum Dots ◽  
Circular Polarization ◽  
Ground State ◽  
Heavy Hole ◽  
Spin Dynamics ◽  
Nuclear Spins ◽  
Time Resolved ◽  
Exciton Ground State ◽  
Charged Exciton

The dynamics of the photoluminescence negative circular polarization of the InP/(In,Ga)P quantum dots ensemble was studied. We find that in the time-resolved dependences of the polarization there are no oscillations in Voigt magnetic field. Also, with increasing field the polarization declines to zero. Such behavior is attributed to the peculiarities of the negatively charged exciton spin dynamics, particularly, to the fact that in the negatively charged exciton ground state the spin dynamics is governed by the heavy hole. We show that magnetic field depolarization of the photoluminescence occurs once the field of dynamically polarized nuclear spins acting on electron spins is surpassed.

scholarly journals Environmentally benign chemical recycling of polycarbonate wastes: comparison of micro- and nano-TiO2 solid support efficiencies

2019 ◽  
Vol 8 (1) ◽  
pp. 108-117 ◽  
Author(s):  
Samira Emami ◽  
Mir Mohammad Alavi Nikje
Keyword(s):  
Titanium Dioxide ◽  
Solid Support ◽  
Conventional Heating ◽  
Gas Chromatography Mass Spectrometry ◽  
Metal Catalyst ◽  
Chemical Recycling ◽  
Solid Supports ◽  
H Nmr ◽  
Optical Discs ◽  
Green System

Abstract Polycarbonate (PC) wastes, including optical discs (CDs) and digital optical discs (DVDs), were chemically recycled into valuable materials such as 4,4′-(propane-2,2-diyl)diphenol (BPA) and etherified derivatives of BPA using sodium hydroxide (NaOH) as the alkali metal catalyst and nanostructured titanium dioxide (nano-TiO2) and microstructured titanium dioxide (micro-TiO2) as the solid supports in the binary green system consisting of water and 2,2′-oxydi(ethan-1-ol) (DEG) under conventional heating method, and data were compared. In this study, the effects of various parameters, such as solvent composition, concentration of NaOH, and solid support, were studied on the reaction progress. In these reactions, the importance of water as the green solvent was investigated in achieving pure BPA as the valuable material. When used with 20% aqueous DEG (pbw), a pure BPA can be obtained at 70% yield in the presence of nano-TiO2 and micro-TiO2 as the solid supports. According to the results, the use of nano-TiO2 in comparison with micro-TiO2 accelerates the chemical recycling of PC wastes. The nano-TiO2 catalyst recovery shows that the recovered solid support is applicable for four cycles. The obtained products were characterized using spectroscopic methods, namely, 1H NMR, 13C NMR, and Fourier transform infrared spectroscopy as well as gas chromatography-mass spectrometry.

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