O ne of the early triumphs of quantum mechanics was Heisenberg's prediction, based on the Pauli principle and wave function symmetry arguments, that the simplest molecule, H 2 , should exist as two distinct speciessallotropes of elemental hydrogen. One allotrope, termed para-H 2 (pH 2 ), was predicted to be a lower energy species that could be visualized as rotating like a sphere and possessing antiparallel (vV) nuclear spins; the other allotrope, termed ortho-H 2 (oH 2 ), was predicted to be a higher energy state that could be visualized as rotating like a cartwheel and possessing parallel (vv) nuclear spins. This remarkable prediction was confirmed by the early 1930s, and pH 2 and oH 2 were not only separated and characterized but were also found to be stable almost indefinitely in the absence of paramagnetic "spin catalysts", such as molecular oxygen, or traces of paramagnetic impurities, such as metal ions.The two allotropes of elemental hydrogen, pH 2 and oH 2 , may be quantitatively incarcerated in C 60 to form endofullerene guest@host complexes, symbolized as pH 2 @C 60 and oH 2 @C 60 , respectively. How does the subtle difference in nuclear spin manifest itself when hydrogen allotropes are incarcerated in a buckyball? Can the incarcerated "guests" communicate with the outside world and vice versa? Can a paramagnetic spin catalyst in the outside world cause the interconversion of the allotropes and thereby effect a chemical transformation inside a buckyball? How close are the measurable properties of H 2 @C 60 to those computed for the "quantum particle in a spherical box"? Are there any potential practical applications of this fascinating marriage of the simplest molecule, H 2 , with one of the most beautiful of all molecules, C 60 ? How can one address such questions theoretically and experimentally?A goal of our studies is to produce an understanding of how the H 2 guest molecules incarcerated in the host C 60 can "communicate" with the chemical world surrounding it. This world includes both the "walls" of the incarcerating host (the carbon atom "bricks" that compose the wall) and the "outside" world beyond the atoms of the host walls, namely, the solvent molecules and selected paramagnetic molecules added to the solvent that will have special spin interactions with the H 2 inside the complex. In this Account, we describe the temperature dependence of the equilibrium of the interconversion of oH 2 @C 60 and pH 2 @C 60 and show how elemental dioxygen, O 2 , a ground-state triplet, is an excellent paramagnetic spin catalyst for this interconversion. We then describe an exploration of the spin spectroscopy and spin chemistry of H 2 @C 60 . We find that H 2 @C 60 and its isotopic analogs, HD@C 60 and D 2 @C 60 , provide a rich and fascinating platform on which to investigate spin spectroscopy and spin chemistry. Finally, we consider the potential extension of spin chemistry to another molecule with spin isomers, H 2 O, and the potential applications of the use of pH 2 @C 60 as a source of latent massive nu...

The recent synthesis 1 of H 2 @C 60 and D 2 @C 60 has provided photochemists with an opportunity to investigate whether the simplest molecule, H 2 , incarcerated inside a fullerene, can communicate with the electronically excited walls of its fullerene container and with excited molecules in the "outside world". 2 We report investigations comparing the photophysical characteristics of triplet C 60 and triplet H 2 @C 60 and the quenching of singlet molecular oxygen, 1 O 2 by C 60 , H 2 @C 60 , and D 2 @C 60 . For comparison, the quenching of 1 O 2 by H 2 and D 2 in solution is reported for the first time. Although the interactions of hydrogen with the walls of triplet C 60 were found to be too weak to be determined by either triplet-triplet absorption or EPR spectroscopy, we report a significant interaction between singlet molecular oxygen ( 1 O The interaction of incarcerated H 2 and D 2 with the walls of triplet fullerene was examined by laser flash photolysis, employing pulses from a Nd:YAG laser (532 nm, ∼5 ns pulse width). C 60 shows a triplet-triplet absorption centered at 747 nm, which was utilized to determine the triplet lifetimes of C 60 , H 2 @C 60 , and D 2 @C 60 in benzene solutions. No differences in the triplet lifetimes were observed within our experimental error (τ ) 110 ( 8 µs; for further details see Supporting Information). Thus, the interaction of incarcerated H 2 and D 2 with the paramagnetic walls of the triplet fullerene is too weak to be determined by triplet lifetime measurements.The magnitude of the interaction of incarcerated H 2 and D 2 with the triplet fullerene was also examined by time-resolved EPR (TREPR). TREPR spectra and transient decay kinetics of C 60 , H 2 @C 60 , and D 2 @C 60 were studied in benzene, toluene, and methylcyclohexane at 285 K. No differences in the spectra and transient decay kinetics of 3 C 60 , H 2 @ 3 C 60 , and D 2 @ 3 C 60 were found.Although there was no measurable interaction of incarcerated H 2 or D 2 with the triplet walls of C 60 , we searched for an interaction with the incarcerated H 2 and D 2 with an external electronically excited molecule, singlet molecular oxygen, 1 O 2 .Large differences in the quenching of 1 O 2 by H-X and D-X bonds are well-known. 3 To the best of our knowledge, there are no reports of the rate constants for quenching of 1 O 2 by H 2 or D 2 in solution, although a large isotope effect is found in the gas phase. 4 It was therefore of interest to determine the quenching rate constants of 1 O 2 by H 2 and D 2 in solution and to compare these rate constants with those for H 2 @C 60 and D 2 @C 60 in solution.The absolute quenching rate constants of 1 O 2 by H 2 @C 60 and D 2 @C 60 were determined using a time-resolved method, employing the host, C 60 , which is known to be an efficient 1 O 2 sensitizer. 5 CS 2 was selected as solvent based on the relatively long lifetime of 1 O 2 (τ ) 79 ms) 6 and high solubility of C 60 in CS 2 (7.9 mg/ mL). 7 The 1 O 2 quenching was monitored by its characteristic phosphorescence at 1270 nm. ...

In a search for alkane candidates for 193 nm immersion fluids, several alkanes and cycloalkanes were synthesized, purified, and screened to ascertain their absorption at 193 nm, refractive index, and temperature dispersion coefficient in the context of the actual application. In general, cycloalkanes, and more specifically polycycloalkanes, possess a higher refractive index than do linear alkanes. Decalin, cyclodecane, perhydrophenanthrene (PHP), perhydrofluorene (PHF), and perhydropyrene (PHPY) are examined as potential second- and third-generation immersion fluids. The use of perhydropyrene, which possesses a high refractive index of 1.7014 at 193 nm, may be limited as an immersion fluid because of high absorption at 193 nm. Mixtures of cycloalkanes can lead to a higher enhancement of the refractive index together with a decrease of the viscosity. Exhaustive purification of the fluids is a critical step in determining the real absorption of the different fluids at 193 nm. Even very small traces of impurities possessing a high absorption coefficient at 193 nm can lead to an unacceptably high level absorption at 193 nm, previously incorrectly attributed to the alkane instead of the absorbing impurities.

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Steady-state and time-resolved fluorescence measurements are reported for several crude oils and their saturates, aromatics, resins, and asphaltenes (SARA) fractions (saturates, aromatics and resins), isolated from maltene after pentane precipitation of the asphaltenes. There is a clear relationship between the American Petroleum Institute (API) grade of the crude oils and their fluorescence emission intensity and maxima. Dilution of the crude oil samples with cyclohexane results in a significant increase of emission intensity and a blue shift, which is a clear indication of the presence of energy-transfer processes between the emissive chromophores present in the crude oil. Both the fluorescence spectra and the mean fluorescence lifetimes of the three SARA fractions and their mixtures indicate that the aromatics and resins are the major contributors to the emission of crude oils. Total synchronous fluorescence scan (TSFS) spectral maps are preferable to steady-state fluorescence spectra for discriminating between the fractions, making TSFS maps a particularly interesting choice for the development of fluorescence-based methods for the characterization and classification of crude oils. More detailed studies, using a much wider range of excitation and emission wavelengths, are necessary to determine the utility of time-resolved fluorescence (TRF) data for this purpose. Preliminary models constructed using TSFS spectra from 21 crude oil samples show a very good correlation (R 2 > 0.88) between the calculated and measured values of API and the SARA fraction concentrations. The use of models based on a fast fluorescence measurement may thus be an alternative to tedious and time-consuming chemical analysis in refineries. ' INTRODUCTIONOnline remote characterization and real-time classification of crude petroleum are the most important current challenges faced by the petrochemical industry and environmental agencies. A rapid and inexpensive method for the remote analysis and classification of petroleum prior to distillation of the crude would provide chemical information of great importance for real-time adjustment of the critical operational parameters of a refinery, permitting an optimization of the process and resulting in economic and environmental benefits.A variety of spectroscopic techniques have been used over the last few decades for the analysis, characterization, and classification of crude oil in drilling fields, for the analysis of petroleum products, and for the detection of oil spills. The advantages of using such techniques include rapid response, the requirement of minimal sample preparation, and relatively inexpensive equipment costs. Of all of the optical spectroscopic techniques employed, vibrational [infrared (IR) and Raman] 1,2 and electronic [ultravioletÀvisible (UVÀvis) and fluorescence] spectroscopies have shown the highest potential in the field. Fluorescence is a more complex phenomenon than absorption (UVÀvis or IR), and effects such as quenching and energy transfer have to be considered. 3,...

An investigation based on confocal fluorescence lifetime imaging microscopy (FLIM) of silica-loaded silicone films doped with a molecular oxygen-sensitive ruthenium(II) polyazaheterocyclic complex is presented. The effect of the silica type (hydrophilic/hydrophobic), particle size and amount of silica filler on the luminescence decay of the immobilized indicator dye has thoroughly been studied. A higher amount of hydrophilic silica leads to both a higher solubility of molecular oxygen into the silicone film and to higher levels of the metal indicator dye. Thus, incorporation of 10% (by wt) pyrogenic silica into silicone shortens the mean luminescence lifetime from 1.4 to 0.9 micros. However, an excess of filler may lead to overloading of the dye into the film producing new phenomena such as triplet-triplet annihilation and excitation energy homotransfer, as observed from their influence on the emission lifetime of the metal complex. Those phenomena do not take place when trimethylated silica (hydrophobic filler) is used. In this case, no increase on the oxygen or dye concentration is observed after addition of the filler and no significant reduction of the luminescence lifetime is measured. Both the addition of silica and the possible precipitation of dye crystals lead to the appearance of microdomains where the molecular probe exhibits widely different excited state lifetimes. For the first time, such microdomains within the oxygen sensing layer are visualized and analyzed by means of FLIM, showing the potential of this technique and the usefulness of our conclusions to the future design and development of novel luminescent oxygen sensor films for environmental and process analysis.

Aerosols of submicron polystyrene particles were oxidized by either vacuum-ultraviolet (VUV) irradiation in the presence of molecular oxygen (O(2)) and/or by ozone (O(3)). Different degrees of oxidation and oxidative degradation were reached by VUV-photolysis depending on radiant energy, O(2) and H(2)O concentrations in the bulk gas mixture as well as on particle diameter. The same functionalization was obtained by exposing the aerosol to O(3), however, oxidation, in particular oxidative degradation, was less efficient. The evolution of hydroxyl and carbonyl functions introduced was quantified by ATR-FTIR spectroscopy of filtered particles, and oxidative degradation of the polymer particles was confirmed by determining size and number of aerosol particles before and after oxidation. Efficiency analyses are based on the results of an O(3) actinometry and on an evaluation of the rate of absorbed photons by the aerosol particles in function of their size.

Covalent tethering of a Ru(II) dye to gallium nitride surfaces has been accomplished as a key step in the development of innovative sensing devices in which the indicator support (semiconductor) plays the role of both support and excitation source. Luminescence emission decays and time-resolved emission spectra confirm the presence of the dye on the semiconductor surfaces, while X-ray photoelectron spectroscopy proves its covalent bonding. The O(2) sensitivity of the new device is comparable to those of other ruthenium-based sensor systems. This achievement paves the way to a new generation of integrable ultracompact microsensors that combine semiconductor emitter-probe assemblies.