Time-resolved Diffuse Reflectance Spectroscopy Research Articles

Cooperative Photochemical Reaction in Molecular Crystal Induced by Intense Femtosecond Laser Excitation: Photochromism of Spironaphthooxazine

Photochromism of indolinospironaphthooxazine (SNO) microcrystalline powder was investigated by steady state and time-resolved diffuse reflectance spectroscopy using a femtosecond laser as a light source. When laser intensity is weak, the photoinduced ring-opening reaction in a picosecond time region and subsequent thermal ring-closure one in a nanosecond scale take place in the crystal, not leading to permanent photocoloration of the powder. The same sample shows photochromism upon intense femtosecond laser excitation. The absorption spectra after laser excitation are similar to those of the photocolored form in solution. The spectral shape is independent of the laser fluence, whereas the yield increases nonlinearly with the fluence. To reveal the photocoloration mechanism, we examined the excitation fluence dependence of the transient absorption spectra and elucidated the photocoloration behavior by femtosecond double pulse excitation varying the delay of the two pulses. These experimental results show t...

Propagation of Femtosecond White-Light Continuum Pulse in Polymer Latex Powder Investigated by Optical Kerr Gate and Time-Resolved Diffuse Reflectance Spectroscopy

Propagation of a femtosecond white-light continuum pulse (350 fs) in poly (methyl methacrylate) (PMMA) latex powders with particle diameters of 1, 5, 20, 60, and 100 µm was investigated by means of an optical Kerr gate and time-resolved diffuse reflectance spectroscopy, which is a pump-probe technique for multiple light scattering materials. The temporal profile of a diffuse reflected light pulse from the powder and the temporal response of transient absorption of the powder doped with an organic molecule were measured. The Kubelka-Munk model was extended to address the propagation of a short light pulse, and its numerical simulations reproduced both experimental results quite well. It is suggested that in a dense scattering medium such as powder, an effect that light is confined or proceeds in a twisted manner is of importance. Fitting the experimental data with the diffusion theory was unsuccessful, which is also discussed.

Charge Carrier Dynamics of Standard TiO2 Catalysts Revealed by Femtosecond Diffuse Reflectance Spectroscopy

Dynamics of charge carriers generated by femtosecond UV (160 fs, 390 nm) excitation in five standard TiO2 photocatalytic powders (JRC-TIO-1, -2, -3, -4, and -5 supplied by the Catalysis Society of Japan) in a vacuum and air was investigated by means of time-resolved femtosecond diffuse reflectance spectroscopy, and was discussed from the viewpoints of crystal structure (anatase and rutile), particle size, and surrounding condition around the particles. Anatase TiO2 catalysts showed very rapid (less than 1 ps) and very slow electron−hole recombination processes, while rutile ones did not show any rapid decay. For catalysts composed of small particles, slower electron−hole recombination was observed in air compared with that in a vacuum, which was well explained in terms of upward band bending near the surface due to adsorption of oxygen. The relationship between the observed charge carrier dynamics and photocatalytic reactivity is also discussed.

Photoinduced Coupling of Acetylenes and Quinone in the Solid State as Preorganized Donor-Acceptor Pairs.

Crystalline electron donor-acceptor (EDA) complexes of various diarylacetylenes (DA) and dichlorobenzoquinone (DB) are isolated and structurally characterized by X-ray crystallography. Deliberate excitation of either the DB acceptor at lambda(DB) = 355 nm or the 1:2 [DA, 2DB] complex at lambda(CT) = 532 nm in the solid state leads to [2 + 2] cycloaddition and identical (isomeric) mixtures of the quinone methide products. Time-resolved (ps) diffuse reflectance spectroscopy identifies the ion-radical pair [DA(*+), DB(*-)] as the reactive intermediate derived by photoinduced electron transfer in both photochemical procedures. The effects of crystal-lattice control on the subsequent ion-radical pair dynamics are discussed in comparison with the same photocouplings of acetylenes and quinone previously carried out in solution.

Does Interfacial Charge Transfer Compete with Charge Carrier Recombination? A Femtosecond Diffuse Reflectance Investigation of TiO2 Nanoparticles

The charge carrier dynamics of opaque, aqueous suspensions of Degussa P-25 TiO2 are probed with femtosecond time-resolved diffuse reflectance spectroscopy. Comparison of ultrafast pump−probe diffuse reflectance measurements of P-25 suspensions with dry P-25 powder and the transient absorption of transparent, aqueous Q-TiO2 solutions allows the observed kinetics to be assigned to charge carrier recombination. The electron−hole recombination kinetics are consistent with a second-order process as demonstrated by a laser fluence dependence study. Interfacial hole transfer dynamics of the P-25 TiO2/SCN- complex are probed as a function of thiocyanate ion concentration. A dramatic increase in the population of trapped charge carriers is observed within the first few picoseconds, demonstrating that interfacial charge transfer of an electron from the SCN- to a hole on the photoexcited TiO2 effectively competes with electron−hole recombination on an ultrafast time scale. The experimental dependence of the charge c...

Time-resolved diffuse reflectance of electron trapping by alkali-metal cation clusters in zeolites and clays following far-UV Excitation

Electron trapping by cation clusters such as Na44+, Na33+, Na22+ and K33+ in zeolites (NaGaY, L and mordenite) and in clay (laponite), following excitation with far-UV light (193 nm), has been studied using time-resolved diffuse reflectance spectroscopy. The results indicate that the trapping of electrons by clusters of charge-balancing cations is an intrinsic property of the zeolite structures. The trapping sites are present only in the crystalline zeolites, not in their amorphous precursors. For the zeolites with channels, such as zeolite L and mordenite, K32+-trapped electrons are observed in the former, while Na32+- and Na2+-trapped electrons are seen in the latter. For laponite (layered structure), electron trapping by Nann+ clusters is also observed, and gives spectral absorption in the region 450–800 nm. The possible locations of trapped electrons in the zeolites are discussed on the basis of their cation locations. The studies correlate the nature of the solid structure with the configuration of the trapped electrons.

Photophysical properties of pyrene in zeolites. Observation of pyrene anion radicals in zeolites X and Y

Formation of pyrene anion radicals in the supercages of zeolites X and Y on photoexcitation is observed by using direct time-resolved diffuse reflectance spectroscopy, and the pyrene anion radical is found to co-exist with the pyrene cation radical.

Photophysical properties of pyrene in zeolites 3. A direct time-resolved diffuse reflectance study in alkali cation-exchanged zeolites X and Y

Time-resolved diffuse reflectance spectroscopy is used to investigate the photolysis of pyrene (Py) impregnated alkali cation-exchanged zeolites X and Y. These studies suggest that pyrene molecules are distributed in at least two different sites (active and non-active) on the zeolites X and Y. Excitation of pyrene adsorbed in non-active sites produces singlet excited states of pyrene with characteristic spectrum and photoionized species by absorbing a second photon, and triplet excited states through inter-system crossing; however, pyrene adsorbed in active sites is photoionized through a single-photon process. The products of the photoionization are the cation radical of pyrene and the ionized electron that is captured by the zeolite framework cation (e.g. Na 3+ 4 for sodium-exchanged zeolite Y). The absorption spectrum of the captured electron in the zeolite framework cation depends on the alkali cation exchanged. Coadsorbed water blocks the oxygen quenching of 3Py* and trapped electron whereas the absorption spectrum of the trapped electron shifts to about 620 nm regardless of the alkali cation exchanged in the zeolite.

Single-photon ionization of pyrene and anthracene giving trapped electrons in alkali-metal cation-exchanged zeolites X and Y: a direct time-resolved diffuse reflectance study

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSingle-photon ionization of pyrene and anthracene giving trapped electrons in alkali-metal cation-exchanged zeolites X and Y: a direct time-resolved diffuse reflectance studyKai Kong Iu and J. K. ThomasCite this: J. Phys. Chem. 1991, 95, 2, 506–509Publication Date (Print):January 1, 1991Publication History Published online1 May 2002Published inissue 1 January 1991https://doi.org/10.1021/j100155a002RIGHTS & PERMISSIONSArticle Views196Altmetric-Citations68LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (423 KB) Get e-Alerts

The use of time-resolved diffuse reflectance spectroscopy to observe transient absorption in transition-metal-ion doped zinc oxide powders

The use of time-resolved diffuse reflectance spectroscopy to observe transient absorption in transition-metal-ion doped zinc oxide powders