Photochemical Reaction Dynamics Research Articles

Irreversible Organic Crystalline Chemistry Monitored in Real Time

Because multiple laser shots are typically required to monitor ultrafast photochemical reaction dynamics, sample depletion and product accumulation have greatly restricted the range of substrates and structural environments amenable to study. By implementing a two-dimensional spatial delay gradient across the profile of a femtosecond probe pulse, we can monitor in a single laser shot organic crystalline reaction dynamics despite the formation of permanent photoproducts that cannot be conveniently removed. We monitored the photolysis of the triiodide anion, I3-, and subsequent recombination or relaxation of its reaction products, in three very different pure organic molecular crystals. The experimental results and associated molecular dynamics simulations illustrate the intimate connection between lattice structure and reaction dynamics, highlighting the role of lattice constraints in directing phase-coherent geminate recombination of photofragments within a crystalline reaction cage.

Femtosecond Real-Time Pump-Probe Imaging Spectroscopy Implemented on a Single Shot Basis

Real-time pump-probe imaging spectroscopy implemented on a single shot basis applicable to photochemical reaction dynamics in biological and organic materials is demonstrated in femtosecond time regime. Using this method, the accumulation time to measure transient signals becomes dramatically reduced, and we can successfully map time–frequency two-dimensional image of the absorbance changes of β-carotene in real-time with an accumulation of 20 laser shots.

Intracellular kinetics of ATX-S10⋅Na(II) and its correlation with photochemical reaction dynamics during a pulsed photosensitization process: effect of pulse repetition rate

Although photodynamic therapy with pulsed light excitation has interesting characteristics, its photosensitization mechanism has not been fully elucidated. In this study, we showed that the intracellular kinetics of ATX-S10.Na(II), a lysosomal sensitizer, was closely related to photochemical reaction dynamics during photodynamic treatment of A549 cells with nanosecond pulsed light. Fluorescence microscopy revealed that at high frequencies of 10 and 30 Hz the sensitizer initially localized mainly in lysosomes but that it started to be redistributed to the cytosol in certain ranges of radiant exposures. These ranges were found to coincide with a regime of fluorescence degradation with limited oxygen consumption. On the other hand, at 5 Hz, there was no such a discontinuous behavior in the sensitizer redistribution characteristics throughout the period of irradiation; this was consistent with the fact that no reaction switching was observed. Two possible reasons for the appearance of the regime with limited oxygen consumption are discussed: participation of an oxygen-independent reaction and change in the microenvironment for the sensitizer caused by lysosomal photodamage. The pulse frequency-dependent intracellular kinetics of the sensitizer also explains our previous results showing higher cytotoxicity at 5 Hz than at 10 and 30 Hz.

The Phase‐dependent Photochemical Reaction Dynamics of Halooxides and Nitrosyl Halides¶

AbstractRecent progress in understanding the phase‐dependent reactivity of halooxides and nitrosyl halides is outlined. Halooxide reactivity is represented by the photochemistry of chlorine dioxide (OCIO) and dichlorine monoxide (CIOCI). The gas phase photochemical dynamics of OCIO are contrasted with the dynamics in condensed environments. The role of excited‐state symmetry in defining the reaction dynamics and the observation of photoisomerization resulting in the production of CIOO are discussed. The current understanding of the excited‐state reaction dynamics of CIOCI and evidence for photoisomerization of this species resulting in the production of CICIO are outlined. Finally, the photochemical reaction dynamics of the nitrosyl halide CINO are presented. The main difference between the gas and condensed phase reaction dynamics of this species is that whereas photodissociation to form CI and NO dominates the gas phase reaction dynamics, photoisomerization resulting in CION production occurs to an appreciable extent in condensed environments. The observation of photoisomerization for OCIO, CIOCI and CINO suggests that this process is a general feature of the condensed phase reaction dynamics for smaller halooxides and nitrosyl halides. Finally, future areas for study in both halooxide and nitrosyl halide photoreactivity are outlined.

Photochemical reaction dynamics of 9,10-phenanthrenequinone and 1,2-naphthoquinone with hydrogen donors in solution

Photoreaction dynamics of 9,10-phenanthrenequinone (PQ) and 1,2-naphthoquinone (NQ) in solution has been studied by laser flash photolysis technique. The real-time transient absorption measurements found out: (1) by excitation at 355 nm in the presence of alcohol, absorption band characteristic to the quinone ketyl radical emerged as the triplet–triplet (T–T) absorption of the quinone submerged, (2) the rise of the absorption of the ketyl radical consisted of two components; the fast and slow ones, where the fast one had the rise rate constant corresponding to the decay rate of triplet quinone, while the slow one rose up much slowly. The experimental fact clearly revealed that the slow reaction should give rise to formation of the ketyl radical following the hydrogen abstraction of triplet PQ and NQ from alcohol, and should be attributed to the hydrogen atom transfer between the parent quinone in the ground state and counter α-hydroxyalkyl radical produced from alcoholic molecule. The reaction mechanism of the ketyl radical formation was thoroughly discussed in the text. The notable reactivity toward hydrogen abstraction of the triplet o-quinones was also discussed.

Multi-mode–multi-state quantum dynamics of key five-membered heterocycles: spectroscopy and ultrafast internal conversion

The multi-mode and multi-state vibronic interactions in the heterocyclic molecules furan, pyrrole, thiophene and their radical cations are investigated theoretically, employing a linear vibronic coupling scheme. The underlying system parameters are determined from large-scale ab initio computations. Previous time-independent dynamical calculations on the radical cations are extended by wave-packet propagations (using the MCTDH method) confirming the strong nonadiabatic coupling effects. For the singlet excited states of furan and thiophene quantum dynamical calculations are presented which go beyond the two-state approximation frequently applied in the literature. The characteristic spectral structures are well reproduced, especially in the case of furan. The implications of these results on the photochemical reaction dynamics of these species are discussed.

The Phase-dependent Photochemical Reaction Dynamics of Halooxides and Nitrosyl Halides¶

Recent progress in understanding the phase-dependent reactivity of halooxides and nitrosyl halides is outlined. Halooxide reactivity is represented by the photochemistry of chlorine dioxide (OClO) and dichlorine monoxide (ClOCl). The gas phase photochemical dynamics of OClO are contrasted with the dynamics in condensed environments. The role of excited-state symmetry in defining the reaction dynamics and the observation of photoisomerization resulting in the production of ClOO are discussed. The current understanding of the excited-state reaction dynamics of ClOCl and evidence for photoisomerization of this species resulting in the production of ClClO are outlined. Finally, the photochemical reaction dynamics of the nitrosyl halide ClNO are presented. The main difference between the gas and condensed phase reaction dynamics of this species is that whereas photodissociation to form Cl and NO dominates the gas phase reaction dynamics, photoisomerization resulting in ClON production occurs to an appreciable extent in condensed environments. The observation of photoisomerization for OClO, ClOCl and ClNO suggests that this process is a general feature of the condensed phase reaction dynamics for smaller halooxides and nitrosyl halides. Finally, future areas for study in both halooxide and nitrosyl halide photoreactivity are outlined.

The phase-dependent photochemical reaction dynamics of halooxides and nitrosyl halides.

Recent progress in understanding the phase-dependent reactivity of halooxides and nitrosyl halides is outlined. Halooxide reactivity is represented by the photochemistry of chlorine dioxide (OClO) and dichlorine monoxide (ClOCl). The gas phase photochemical dynamics of OClO are contrasted with the dynamics in condensed environments. The role of excited-state symmetry in defining the reaction dynamics and the observation of photoisomerization resulting in the production of ClOO are discussed. The current understanding of the excited-state reaction dynamics of ClOCl and evidence for photoisomerization of this species resulting in the production of ClClO are outlined. Finally, the photochemical reaction dynamics of the nitrosyl halide ClNO are presented. The main difference between the gas and condensed phase reaction dynamics of this species is that whereas photodissociation to form Cl and NO dominates the gas phase reaction dynamics, photoisomerization resulting in ClON production occurs to an appreciable extent in condensed environments. The observation of photoisomerization for OClO, ClOCl and ClNO suggests that this process is a general feature of the condensed phase reaction dynamics for smaller halooxides and nitrosyl halides. Finally, future areas for study in both halooxide and nitrosyl halide photoreactivity are outlined.

The Phase-dependent Photochemical Reaction Dynamics of Halooxides and Nitrosyl Halides¶

Recent progress in understanding the phase-dependent reactivity of halooxides and nitrosyl halides is outlined. Halooxide reactivity is represented by the photochemistry of chlorine dioxide (OClO) and dichlorine monoxide (ClOCl). The gas phase photochemical dynamics of OClO are contrasted with the dynamics in condensed environments. The role of excited-state symmetry in defining the reaction dynamics and the observation of photoisomerization resulting in the production of ClOO are discussed. The current understanding of the excited-state reaction dynamics of ClOCl and evidence for photoisomerization of this species resulting in the production of ClClO are outlined. Finally, the photochemical reaction dynamics of the nitrosyl halide ClNO are presented. The main difference between the gas and condensed phase reaction dynamics of this species is that whereas photodissociation to form Cl and NO dominates the gas phase reaction dynamics, photoisomerization resulting in ClON production occurs to an appreciable extent in condensed environments. The observation of photoisomerization for OClO, ClOCl and ClNO suggests that this process is a general feature of the condensed phase reaction dynamics for smaller halooxides and nitrosyl halides. Finally, future areas for study in both halooxide and nitrosyl halide photoreactivity are outlined.

Kinetic Model for Determination of Reaction and Polarization Dynamics from Chemically Induced Electron Spin Polarized Electron Spin Resonance Spectra

The dynamics of photochemical reactions exhibiting chemically induced electron spin polarization (CIDEP) are modeled by kinetic equations that include all relevant parameters, including reaction of the excited precursor as both a singlet and a triplet and spin exchange during radical encounters. Analysis of the acetone/2-propanol photolysis reveals spin exchange effects and provides further evidence that the anomalous net electron spin resonance (ESR) absorption of the 2-propanolyl radical is due to spin−lattice relaxation in the triplet acetone precursor. The weakening of this net absorption in acetone/triethylamine photolyses is due to the rapid reaction of photoexcited acetone with triethylamine resulting in reaction via both its singlet state, which cannot produce a net polarization, and its triplet state, which yields no triplet polarization and reacts before spin−lattice relaxation can produce full equilibrium polarization.

Investigating the phase-dependent photochemical reaction dynamics of chlorine dioxide using resonance Raman spectroscopy

Recent progress in understanding the phase-dependent reactivity demonstrated by halooxides is outlined. Specifically, resonance Raman intensity analysis (RRIA) and time-resolved resonance Raman (TRRR) studies of chlorine dioxide (OClO) photochemistry in solution are presented. Using RRIA, it has been determined that the excited-state structural evolution that occurs along the asymmetric-stretch coordinate in the gas phase is restricted in solution. The absence of evolution along this coordinate results in the preservation of groundstate symmetry in the excited state. The role of symmetry in defining the reaction coordinate and the solvent-solute interactions responsible for modification of the excited-state potential energy surface are discussed. TRRR studies are presented which demonstrate that geminate recombination of the primary photoproducts resulting in the reformation of ground-state OClO is a central feature of OClO photochemistry in solution. These studies also demonstrate that a fraction of photoexcited OClO undergoes photoisomerization to form ClOO, with the ground-state thermal decomposition of this species resulting in Cl production on the subnanosecond timescale. Finally, time-resolved anti-Stokes experiments are presented which demonstrate that the OClO vibrational-relaxation dynamics are solvent dependent. The current picture of OClO photochemistry derived from these studies is discussed, and future directions for study are outlined.

Understanding the phase-dependent reactivity of chlorine dioxide using resonance Raman spectroscopy.

Progress in understanding the phase-dependent reactivity of chlorine dioxide (OClO) is outlined. Resonance Raman intensity analysis studies of gaseous and solution-phase OClO are presented which demonstrate that the optically prepared excited state undergoes significant modification in solution. In addition, time-resolved resonance Raman studies are presented which demonstrate that geminate recombination of the primary photoproducts, resulting in the re-formation of ground-state OClO, dominates the photochemical reaction dynamics in solution. The current picture of aqueous OClO photochemistry derived from these studies is discussed, and future directions of investigation are outlined.

Vibrational mode-specific photochemical reaction dynamics of chlorine dioxide in solution

We study the reaction dynamics of OClO in cyclohexane, acetonitrile, and water by femtosecond pump–probe spectroscopy. In all solvents we observe a quantum beat in a 403 nm one-color pump–probe experiment with 55 fs temporal resolution, that decays with a 1.3–1.5 ps time constant. From this we conclude that, in contrast to previous reports, not all OClO molecules dissociate after excitation with 403 nm light. In both cyclohexane and water we observe in the 403 nm experiment an increase in stimulated emission between 0.5 and 2 ps that appears to be connected to the quantum beat decay. We explain these results as the consequence of vibrational relaxation of the bending mode of OClO. Relaxation from (ν1,1,0) to (ν1,0,0) leads to population of a state with a two times higher transition dipole moment, which accounts for the increased stimulated emission. Further proof that not all OClO molecules dissociate immediately after excitation is found in the identification of a stimulated emission contribution in femtosecond 400 nm pump/800 nm probe experiments, which also decays with about a 1.5 ps time constant. Femtosecond 400 nm pump/267 nm probe measurements indicate that a fraction of the OClO molecules dissociate very rapidly, with dissociation times of ⩽60, 80, and 140 fs, in acetonitrile, water, and cyclohexane, respectively. An anisotropy decay is resolved at 267 nm of the formed ClO in water and cyclohexane, with anisotropy decay times of 0.17 and 0.27 ps, respectively. In all solvents a fraction of the ClO+O fragments recombine, with time constants of 1.2 and 4.1 ps in water, 6.0 ps in acetonitrile, and 8.9 ps in cyclohexane. In acetonitrile a secondary dissociation pathway is identified with a 2.1 ps time constant. This pathway might also be responsible for the biexponentiality of the recombination process in water. In particular, in acetonitrile and cyclohexane the data indicate cage escape of a significant amount of fragments.

Picosecond time-resolved Raman system for studying photochemical reaction dynamics: application to the primary events in vision

A time-resolved Raman system was developed to study the picosecond reaction dynamics of energy and information transducing proteins. This system is based on a 1 kHz Nd : YLF-pumped Ti-sapphire regenerative amplifier that delivers picosecond pump and probe pulses with high temporal and spectral resolution. Using second-harmonic generation and Raman shifting, near transform-limited picosecond pulses are generated at wavelengths ranging from the UV to the near-infrared (190–850 nm) with ∼2 ps temporal width. This laser system, together with a CCD-detected spectrograph, facilitates the performance of picosecond Raman experiments over a much wider range of pump and probe wavelengths than previously possible with low repetition rate amplified dye laser systems. The construction and performance of the laser system is presented first, then single-pulse and two-color, pump–probe experiments examining the primary reaction dynamics of the visual protein rhodopsin are presented to illustrate the system performance. The strong characteristic hydrogen out-of-plane modes of the bathorhodopsin photoproduct are observed at 850, 873 and 920 cm−1 in the shortest time resolution data. This demonstrates that the trans-bathorhodopsin retinal chromophore structure is completely formed in <2 ps after photoexcitation. Copyright © 1999 John Wiley & Sons, Ltd.

Absorption and Resonance Raman Study of the 2B1(X)−2A2(A) Transition of Chlorine Dioxide in the Gas Phase

The photochemical reaction dynamics of chlorine dioxide (OClO) are investigated using absorption and resonance Raman spectroscopy. The first Raman spectra of gaseous OClO obtained directly on resonance with the 2B1−2A2 electronic transition are reported. Significant scattering intensity is observed for all vibrational degrees of freedom (the symmetric stretch, bend, and asymmetric stretch), demonstrating that structural evolution occurs along all three normal coordinates following photoexcitation. The experimentally measured absorption and resonance Raman intensities are compared to the intensities predicted using both empirical and ab initio models for the optically active 2A2 surface. Comparison of the experimental and theoretical absorption spectra demonstrates that the frequencies and intensities of transitions involving the asymmetric stretch are well reproduced by the empirical model characterized by a double-minimum along the asymmetric stretch. However, the ab initio model is also found to reproduce a subset of the experimental intensities. In addition, the extremely large resonance Raman intensity of the asymmetric stretch overtone transition is predicted by both models. The results presented here taken in combination with the model for the 2A2 surface in condensed environments suggest that the phase-dependent photochemical reactivity of OClO is due to environment-dependent excited-state structural evolution along the asymmetric stretch coordinate.

Comparison of chlorine dioxide photochemistry in acetonitrile and water using subpicosecond pump–probe spectroscopy

The photochemical reaction dynamics of chlorine dioxide (OClO) dissolved in water and acetonitrile are investigated using subpicosecond pump–probe spectroscopy. The spectral dynamics observed at 267 and 400 nm demonstrate that the quantum yield for geminate recombination of ClO and O to form OClO is reduced in acetonitrile relative to water. However, the dynamics at 800 nm are similar for both solvents consistent with ClOO rather than OClO being responsible for the evolution at this wavelength. The kinetics for ground-state ClOO production and decomposition are significantly slower in acetonitrile relative to water suggesting that solvent–solute hydrogen bonding is important in defining the ground state reactivity of this photoproduct.

Dynamics of photochemical reactions: Simulation by quantum calculations for transition metal hydrides

AbstractThe photodissociation dynamics of some organometallic molecules in the lowest repulsive electronically states are reported for the following concurrent primary reactions: (i) the homolysis of a metal–hydrogen bond vs. the heterolytic loss of a carbonyl ligand in HCo(CO)4; (ii) the photoinduced elimination of molecular hydrogen vs. the loss of a carbonyl ligand in H2Fe(CO)4; and (iii) the photoinduced elimination of molecular hydrogen vs. the loss of a mesithylene ligand in H2Os(CO)Mes (Mes = C6H3(CH3))3. The dynamics are simulated quantum mechanically using a time‐dependent wavepacket propagation technique on potential energy surfaces obtained from CASSCF/CCI calculations for HCo(CO)4 and H2Fe(CO)4 and from SCF‐INO/MRCI calculations for H2Os(CO)Mes. This approach gives a rather detailed view of some important elementary processes that contribute to the photochemistry of these complexes. The nature of the photoactive excited states is determined without ambiguity, as well as the time scales, the branching ratio of the different primary dissociation pathways, and some features of the absorption spectra. © 1994 John Wiley &amp; Sons, Inc.

Dynamics of photochemical reactions studied by degenerate four-wave mixing

The scattering efficiency of a transient grating, i.e. the non-linear suscpetibility X (3) (−ω;ω, −ω, ω), gives valuable information of the momentary state of the system. Here, X (3) is first determined for the ground state and - after excitation of the molecule by ultrashort pulses - the subsequent states are investigated. As a first example of the technique, 3-hydroxyflavone in the ground state and the growth and decay of the proton transfer state are reported. The dispersion measured over the large frequency range from 10000 to 30000 cm −1 shows an enormous enhancement of approximately three orders of magnitude near resonances.

Determination of Pericyclic Photochemical Reaction Dynamics with Resonance Raman Spectroscopy

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTDetermination of Pericyclic Photochemical Reaction Dynamics with Resonance Raman SpectroscopyPhilip J. Reid, Mary K. Lawless, Steven D. Wickham, and Richard A. MathiesCite this: J. Phys. Chem. 1994, 98, 22, 5597–5606Publication Date (Print):June 1, 1994Publication History Published online1 May 2002Published inissue 1 June 1994https://doi.org/10.1021/j100073a004RIGHTS & PERMISSIONSArticle Views247Altmetric-Citations69LEARN 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 (3 MB) Get e-Alerts

Laser-enhanced gas surface reaction of chlorine with aluminum polycrystalline surface

The supersonic molecular beam technique is used to investigate the dynamics of photochemical gas-surface reactions of Cl 2 with polycrystalline Al surface irradiated by 355- and 1064-nm laser photons. The mass and velocity distributions of desorbed reaction products are measured by time-resolved mass spectrometry. Results show that the main products are Al + and AlCl x (x=1,2,3) produced with the irradiation at 355 nm; only AlCl 3 is produced under 1064-nm laser irradiation