Organic Molecules In Solution Research Articles

High intensity laser photochemistry of organic molecules in solution

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTHigh intensity laser photochemistry of organic molecules in solutionR. Marshall. Wilson and Karlyn A. SchnappCite this: Chem. Rev. 1993, 93, 1, 223–249Publication Date (Print):January 1, 1993Publication History Published online1 May 2002Published inissue 1 January 1993https://doi.org/10.1021/cr00017a011RIGHTS & PERMISSIONSArticle Views506Altmetric-Citations45LEARN 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 Get e-Alerts

Solution dynamics by line shape analysis, resonance light scattering and femtosecond four-wave mixing

The results of line shape analysis, resonance light scattering and femtosecond four-wave mixing measurements are reported on several organic molecules in solution. It is shown that a Brownian oscillator model for line broadening provides a full description for the optical dynamics in aprotic solutions. The dynamics of all systems studied is found to occur in the intermediate modulation regime, where the amplitude Δ and inverse correlation time Λ of the Brownian oscillator are about equal: Δ/Λ ≈ 1. Isotopic substitution of either probe or solvent is shown to have no effect on the dynamics, from which it is concluded that the vibrational force field plays a minor role in determining the line shape. Four-wave mixing experiments with chirped femtosecond pulses yield intense coherent Raman scattering signals due to ground and excited-state vibrational coherences which are very effectively driven by the two instantaneous light fields whose frequency difference matches exactly a vibrational mode. It is shown that the “chirped” four-wave mixing signal near zero delay time only mimics the two-pulse photon echo if the system dynamics fall in the fast modulation limit: Δ/Λ⪡1. Otherwise this signal is damped not only by dephasing but also by solvation dynamics.

Vibronic coupling in excited electronic states of complex molecules

Different aspects of the theoretical interpretation and utilization of the fine-structure vibronic spectra of polyatomic organic molecules in solution for determining characteristics of the electronic excited states of such molecules, such as the orbital type, localization of excitation on fragments, change of nuclear configuration, etc., are presented. The adiabatic approximation with Frank–Condon and Herzberg–Teller coupling is studied. A great deal of attention is devoted to the phenomenon of suppression of most spectral lines in the range corresponding to allowed transitions in vibronic spectra. Some reasons for this phenomenon are discussed.

Ultrafast vibrational dynamics of small organic molecules in solution

In this paper we present a time-resolved study of the vibrational relaxation after excitation of the asymmetric CH2 stretch vibration of dibromomethane and diiodomethane and the C–H stretch vibration of 1,1,2,2-tetrabromoethane. The experiments were performed in a polar and a nonpolar solvent in order to study the influence of the polarity of the solvent on the relaxation. We observe that in both types of solvent the vibrational energy transfer is successively intra- and intermolecular and that the intramolecular relaxation leads to a shift of the transition frequency of the excited molecular vibration. We discuss the experimentally determined time constants of the relaxation in terms of the energy differences between the molecular vibrations and the interactions with the solvent.

Uv Multiphoton Induced Chemistry of Nitrobenzene in Solution

The technique of Multiphoton Induced Chemistry (MPIC) has been employed to initiate ion‐molecule chemistry of organic molecules in solution. We report one of the first examples of the use of liquid phase multiphoton ionization (MPI) to prepare organic cations, which then react with the solvent in ionmolecule processes. The products obtained in this chemical sequence are significantly different from those observed in conventional or multiphoton‐induced neutral chemistry in the same solvent. The particular example explored in this work is the reactivity of the nitrobenzene cation in methanol solvent. Products of the ion‐molecule chemistry, detected by gas chromatography/mass spectrometry, are phenol and benzyl alcohol. These products depend upon the square of the laser intensity. It is shown by ionization current measurements in a conductance cell, that ionic species are produced as precursors to the observed products. The implications of this application of MPI are briefly discussed. A preliminary report on the unimolecular chemistry of the highly excited neutral molecule is also included. The product of this channel is nitrosobenzene. It is shown, in this case, that the reactive state is most likely a highly vibrationally excited ground state molecule, not the lowest triplet level invoked in conventional photochemistry.

Estimation of ultrashort excited-state lifetimes from Raman-to-fluorescence intensity ratios

Using stochastic theory, the integrated intensity ratio of Raman lines to the total secondary radiation under resonant excitation is shown to correspond to the ratio of the fluorescence decay rate to the homogeneous bandwidth of the absorption spectrum. Excited-state lifetimes of organic molecules in solution estimated using this relation agree well with the available data.

Photophysical hole burning on dye solutions in the liquid phase with ns‐laserpuises

AbstractThe necessary conditions for observing inhomogeneous bleaching of the electronic absorption bands of organic molecules in solution at room temperature have been investigated by simple rate equation models. For systems with ground state recovery times in the ps‐range, photophysical hole burning (PPHB) can be obtained with the ns‐laserpulses. The measured experimental result for crystal violet in acetonitrile may serve as an example. In transitions between excited states PPHB is possible as an universal method on probably all organic molecules. This has been demonstrated for the S1‐absorption band of para‐terphenyl at 570 nm. The given brief outline of methods, results, and conclusions will be described separately in more detail.

Oscillatory femtosecond relaxation of photoexcited organic molecules

The ultrafast relaxation of large organic molecules in solution has been investigated with the transmission correlation technique. The existence of damped sinusoidal decays after photoexcitation has been verified for several organic dyes. This behavior (the first such decay observed on a femtosecond time scale for any material) is explained as quantum beats. For all molecules examined, we have also observed fast initial exponential decays (<100 fs) in addition to previously known picosecond processes.

Dielectric spectroscopy on aqueous solutions of pyridine and its derivatives

The complex (dielectric) permittivity has been measured as a function of frequency between 1 MHz and 40 GHz for aqueous solutions of pyridine, 2- and 3-methylpyridine, as well as 2,4- and 2,6-dimethylpyridine at various temperatures and solute concentrations. Different relaxation spectral functions are used to analytically represent the data, in particular the Cole-Cole function. The solute contribution to the extrapolated static permittivity has been calculated to show that, in correspondence with other aqueous solutions of organic molecules and ions, the permittivity of the solvent seems to be enhanced with respect to the pure water value. Also in accordance with other aqueous systems it is found that the principal dielectric relaxation time for equimolar solutions of stereo isomers at the same temperature may significantly differ from one another. A further result is the finding of an unusually strong temperature dependence in the relaxation time of the 1 molar solution of 2,6-dimethylpyridine.

Proton Spin-Lattice Relaxation Rates in the Structural Analysis of Carbohydrate Molecules in Solution

Publisher Summary This chapter focuses on proton spin–lattice relaxation rates in the structural analysis of carbohydrate molecules in solution. It gives an account of the simple theory related to spin-lattice relaxation-rates; cautions against the uncritical use of this simple theory for systems that are strongly coupled, or undergoing anisotropic reorientation, or both; introduces the pulse nuclear magnetic resonance (NMR) experiments that are used to measure spin–lattice relaxation-rates and to stress the precautions necessary for accurate measurements; discusses the types of experiments that reveal stereo-specific dependencies of spin–lattice relaxation-rates, along with concrete examples from the literature; and assesses the reliability of these experiments and their relative merits as to accuracy and technical simplicity. The proton spin-lattice relaxation-rate (R,) is a well established, NMR parameter for the structural, configurational, and conformational analysis of organic molecules in solution. However, its utility has received little attention in the field of carbohydrate chemistry and very few studies have been reported in which relaxation rates were used to extract qualitative or quantitative information, or both, about the geometry of carbohydrate molecules in solution. The chapter also provides details on the stereochemical implications of relaxation rates and explains the limitations and relative merits of relaxation methods.

Reactivity of carboxylic acid and ester groups in the functionalized interfacial region of "polyethylene carboxylic acid" (PE-CO2H) its derivatives: differentiation of the functional groups into shallow and deep subsets based on a comparison of contact angle and ATR-IR measurements

We have differentiated the carboxylic acid groups present in the functionalized interface of “polyethylene carboxylic acid” (PE4O2H, a material prepared from low-density polyethylene film by reaction with aqueous chromic acid) into two subsets: those sufficiently close to the surface of the polymer to influence its wettability by water and those too deep to do so. This differentiation was accomplished by taking advantage of differences in rates of esterification of carboxylic acid groups in different regions of the functionalized interface and of differences in rates of hydrolysis of ester groups derived from them. The subset of functional groups influencing wettability comprises <30% of the total groups present in the functionalized interface and appears to be homogeneous in its chemical reactivity. The remaining groups (-70% of the total) do not directly influence wettability and appear to become less reactive with increasing depth in the polymer. The surface and subsurface carboxylic acid and ester moieties are both less reactive in hydrolysis and formation reactions than are these groups in organic molecules in solution. Reactivities of the interfacial functional groups depend on structure in ways having no analogy in reactions in solution. For example, the rate of base-catalyzed hydrolysis of esters present in the functionalized polymer interface is a strong function of the length of the alcohol component of the ester: n-octyl esters are more than 20000 times less reactive than methyl esters. We have also explored the acidity of the interfacial carboxylic acid groups using ATR-IR spectroscopy and contact angle measurements as probes. Both the local polarity of the environment of individual carboxylic acid groups and charge-charge interactions between carboxylate anions appear to be important in determining acidity. Comparisons of wettability of samples containing different proportions of carboxylic acid, carboxylate anion, and ester groups indicate that wettability is particularly sensitive to low concentrations of carboxylate anion. We hypothesize that this sensitivity reflects a limited ability of the functionalized interfacial region to reconstruct-perhaps only by small-amplitude rotations of its constituent carboxylate ions-in a way that minimizes its free energy by maximizing the number of these hydrophilic moieties in direct contact with the polar, aqueous liquid phase.

The role of mixing time in 2D heteronuclear NOE experiments

Heteronuclear NOE experiments are promising for the determination of carbonproton distances in organic molecules in solution. A heteronuclear 2D NOE experiment (I, 2) has recently been described for the study of heteronuclear dipole-dipole interactions. In those preliminary reports it is generally accepted that the optimal value of the mixing time (T,,,~) in the pulse sequence depends only on the average proton relaxation time r,. In this note we show that to obtain cross peaks of significant intensities choice of mixing time needs more care. We have verified that the optimum of mixing time depends as well on the pertinent relaxation times Ti of carbon nuclei. To calculate the optimum mixing time (TV. m) we used the two-spin approximation AX, A = ‘H and X = 13C. The time dependence of the peaks in a two-dimensional heteronuclear NOE spectrum can be expressed in a matrix format, similar to the homonuclear case (3-5) add btiR~m)lid ill

ChemInform Abstract: Calixarenes. Part 15. The Formation of Complexes of Calixarenes with Neutral Organic Molecules in Solution (Komplexierung von Toluol durch (Ia).

Chemischer InformationsdienstVolume 17, Issue 5 Article ChemInform Abstract: Calixarenes. Part 15. The Formation of Complexes of Calixarenes with Neutral Organic Molecules in Solution (Komplexierung von Toluol durch (Ia). L. J. BAUER, L. J. BAUERSearch for more papers by this authorC. D. GUTSCHE, C. D. GUTSCHESearch for more papers by this author L. J. BAUER, L. J. BAUERSearch for more papers by this authorC. D. GUTSCHE, C. D. GUTSCHESearch for more papers by this author First published: February 4, 1986 https://doi.org/10.1002/chin.198605089Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume17, Issue5February 4, 1986 RelatedInformation

Comparison of the Excited-state Dipole Moments and Polarizabilities Estimated from Solvent Spectral Shifts with Those from Electrooptical Measurements

Abstract On the assumption that the average energy for all transitions from a low-lying excited state to all other states was approximately the same as that for all transitions from the ground state to all excited states, Abe’s improved expression for the solvent spectral frequency shift (Bull. Chem. Soc. Jpn., 54, 327 (1981)) was applied to spectral data for some neutral organic molecules in solution in order to estimate their excited-state dipole moments and polarizabilities. The changes in the dipole moments and/or polarizabilities of these molecules upon excitation were compared with those obtained from electrooptical measurements. Both methods give results that are consistent.

Indirect, negative heteronuclear Overhauser effect detected in a steady-state, selective 13C{1H} NOE experiment at natural abundance

It has recently been shown that both selective 13C-{1H} NOE measurements (1–10) and non-selective two-dimensional (2D) NOE (11–13) (cross-relaxation) spectroscopy are promising techniques for the determination of carbon-proton distances in organic molecules in solution.

Relaxation of large molecules following ultrafast excitation

We demonstrate that the ultrafast relaxation observed in the excited states of large organic molecules in solution may be understood as the coherent evolution of the initially prepared non-stationary state. it is shown that under femtosecond excitation conditions the relaxation is determined by the characteristics of the light pulse. The analysis of a simple pump-probe experiment suggests a way of measuring the characteristics of ultrashort pulses. The case of fluorescence excited by ultrafast is also analysed.

The static electric permittivity of solutions of organic molecules in dipolar solvents

The permittivity of solutions of pyrazine and of 1,4-diazabicyclo-[2,2,2]-octane (TED) in various dipolar solvents has been measured at 10 MHz by means of a sensitive bridge method. The solvents used were water, methanol, formamide, N-methylformamide, N,N-dimethylformamide, and dimethylsulfoxide. The results of the measurements are compared with those of theoretical mixture formulas. It is shown that — depending on structural properties — the permittivity attributed to the solvation shells around the organic solute molecules is changed with respect to the pure solvent value.

Spectral-polarization characteristics of the luminescence of solutions of organic molecules under light-quenching conditions. The quenching mechanism

Spectral-polarization characteristics of the luminescence of solutions of organic molecules under light-quenching conditions. The quenching mechanism

Site selection spectroscopy of polyatomic molecules: principles, applications and possibilities

Brief review of a new branch in the spectroscopy of complex organic molecules in solutions - Site Selection Spectroscopy - is given. Principles and methods to reveal a line structure in the inhomogeneously broadened absorption and luminescence spectra by means of selective laser excitation are described. Some examples are shown to demonstrate new possibilities of selective methods for precise investigations of: energy levels of organic molecules; electron-phonon interactions; the Zeeman and Stark effects, spectrochemical analysis of complex organic materials, etc.

Site selection spectroscopy of organic molecules in solutions and its applications

Principles and methods to reveal a line structure in inhomogeneously broadened absorption and luminescence spectra of organic molecules in solutions by means of selective laser excitation are briefly described. Examples are given to demonstrate new possibilities of fine spectroscopic studies of complex molecules.