Dimerization and Polymerization of Isoprene at High Pressures

Citroni, Mario; Ceppatelli, Matteo; Bini, Roberto; Schettino, Vincenzo

doi:10.1021/jp0701993

Cited by 38 publications

(39 citation statements)

References 32 publications

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“…In both processes most of the monomer reacts only during decompression, and the recovered amorphous hydrogenated carbons obtained in the two syntheses present the same characteristics. This result indicates that the same reaction mechanism occurs in both cases, which is rather peculiar behavior in comparison with other small unsaturated hydrocarbons, where the structural changes determined by the optical excitation open new reactive paths, as observed in isoprene (17), or select specific ones, as in butadiene (2). In benzene, the molecular geometry is not significantly altered by excitation to the S 1 state; only a moderate lengthening of the C-C bonds (0.03 Å) takes place.…”

Section: Discussionmentioning

confidence: 54%

“…This mixing, tuned by pressure, has been invoked to explain the reaction occurring among neighboring molecules in some large aromatic hydrocarbon crystals (15), but it has also been suggested that the same process can be activated or increased at milder density through the optical excitation of the molecule to a suitable electronic state, as successfully demonstrated for several unsaturated hydrocarbons (16). In addition, a remarkably high selectivity in reaction products can also be achieved in the photoinduced high-pressure polymerization of butadiene (2), ethylene (4), and isoprene (17).…”

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confidence: 96%

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Role of excited electronic states in the high-pressure amorphization of benzene

Citroni¹,

Bini

Foggi

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

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High-pressure methods are increasingly used to produce new dense materials with unusual properties. Increasing efforts to understand the reaction mechanisms at the microscopic level, to set up and optimize synthetic approaches, are currently directed at carbon-based solids. A fundamental, but still unsolved, question concerns how the electronic excited states are involved in the high-pressure reactivity of molecular systems. Technical difficulties in such experiments include small sample dimensions and possible damage to the sample as a result of the absorption of intense laser fields. These experimental challenges make the direct characterization of the electronic properties as a function of pressure by linear and nonlinear optical spectroscopies up to several GPa a hard task. We report here the measurement of two-photon excitation spectra in a molecular crystal under pressure, up to 12 GPa in benzene, the archetypal aromatic system. Comparison between the pressure shift of the exciton line and the monomer fluorescence provides evidence for different compressibilities of the ground and first excited states. The formation of structural excimers occurs with increasing pressure involving molecules on equivalent crystal sites that are favorably arranged in a parallel configuration. These species represent the nucleation sites for the transformation of benzene into amorphous hydrogenated carbon. The present results provide a unified picture of the chemical reactivity of benzene at high pressure.benzene crystal ͉ electronic transitions ͉ high-pressure chemistry ͉ two-photon spectroscopy

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Section: Discussionmentioning

confidence: 54%

mentioning

confidence: 96%

Role of excited electronic states in the high-pressure amorphization of benzene

Citroni¹,

Bini

Foggi

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

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“…It is therefore evident that these reactions become more and more relevant with increasing pressure because the increasing density of the materials results in reduced intermolecular distances that favor the interaction between excited and groundstate molecules. The efficiency of these processes is also attested to by several reactions occurring in pure condensed unsaturated hydrocarbons triggered by 2-photon (TP) excitations realized with cw (continuous wave) low-power laser sources that, because of the small cross-section of TP transitions, ensure catalytic amounts of excited species (5,6,12,15).Among simple molecular systems, water is of primary importance because of its abundance on the Earth's surface and because it is the most abundant polyatomic molecule in the visible universe (16). In addition, chemical reactions taking place in liquid water are essential for many processes in environmental science and biology.…”

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confidence: 99%

High-pressure photodissociation of water as a tool for hydrogen synthesis and fundamental chemistry

Ceppatelli¹,

Bini²,

Schettino³

2009

Proc. Natl. Acad. Sci. U.S.A.

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High-pressure methods have been demonstrated to be efficient in providing new routes for the synthesis of materials of technological interest. In several molecular compounds, the drastic pressure conditions required for spontaneous transformations have been lowered to the kilobar range by photoactivation of the reactions. At these pressures, the syntheses are accessible to large-volume applications and are of interest to bioscience, space, and environmental chemistry. Here, we show that the short-lived hydroxyl radicals, produced in the photodissociation of water molecules by near-UV radiation at room temperature and pressures of a few tenths of a gigapascal (GPa), can be successfully used to trigger chemical reactions in mixtures of water with carbon monoxide or nitrogen. The detection of molecular hydrogen among the reaction products is of particular relevance. Besides the implications in fundamental chemistry, the mild pressure and irradiation conditions, the efficiency of the process, and the nature of the reactant and product molecules suggest applications in synthesis.high-pressure chemistry ͉ photocatalysis T he application to molecular systems of suitable external pressures causes a density increase that determines a strengthening of the intermolecular interactions leading first to changes in the aggregation state of the material, and then to crystalline phase transitions (1). Upon further compression, the possible overlap of the electronic density of nearest-neighbor molecules can also trigger a complete reconstruction of the chemical bonds, giving rise to new materials in some cases recoverable at ambient conditions (2). After the pioneering work on the pressure-induced polymerization of cyanogen (3) and acetylene (4) crystals, several simple molecular crystals have been reported to react upon application of suitable external pressure, giving rise to high-quality polymeric (5-7) and amorphous (8-10) materials of potential technological interest. These transformations require pressures from several to 100 GPa, as in the nitrogen case (7), but the reaction threshold pressure has been successfully lowered in almost all of the unsaturated hydrocarbons studied so far by a photoactivation of the high-pressure reactions (11). In some cases, an increasing selectivity (5) or the opening of new reaction paths (12) is also observed. These syntheses are appealing because only physical methods are used, thus representing an interesting perspective for a green chemistry (13).The mechanisms governing the photoinduced reactivity of molecular systems derive from the structural and charge density distribution changes after an electronic transition. In general, the excited molecule is characterized by a reduced binding order that determines molecular bonds stretching, a lowering of rotational and torsional barriers, an increase in the polarity, and even dissociation and ionization. These species can be particularly aggressive from a chemical point of view and, depending on their lifetime and free mean path, can trigger a...

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“…In addition, in some cases also an increased selectivity (Citroni et al 2002) or the opening of new reaction paths (Citroni et al 2007) has been also observed. The reason of this behavior has to be searched in the structural and charge density distribution changes occurring after an electronic transition.…”

Section: Pressure-induced Reactivity In Molecular Systemsmentioning

confidence: 91%

The role of high-pressure in the reactivity of simple molecules: implications in prebiotic chemistry

Bini

2011

Rend. Fis. Acc. Lincei

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Simple molecules are abundant in several space environments and the knowledge of their physical properties and chemical reactivity is central in many disciplines. Pressure plays a key role in this scenario causing intriguing and unexpected aggregation forms and chemical transformations also for the simplest molecules like water, nitrogen and carbon dioxide. Particularly interesting is the simultaneous effect of pressure and absorption of radiation, a common scenario in spatial environments, because of the electronic changes produced in the molecular systems which result able to trigger chemical processes by exploiting the high-density conditions. Here we will provide some examples of the high-pressure reactivity of few simple model molecules and of their mixtures. These molecules have been selected on the basis of their abundance and relevance in a prebiotic chemical framework. In most of the examples, attention is posed on the comparison between purely pressure-induced and laser-assisted high-pressure reactions in order to account and discriminate the effects of the two variables on the reactivity. The technical approaches employed to reproduce in laboratory, the pressure and temperature conditions of interest for simulating the conditions encountered in different spatial environments will also be briefly reviewed.

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Dimerization and Polymerization of Isoprene at High Pressures

Cited by 38 publications

References 32 publications

Role of excited electronic states in the high-pressure amorphization of benzene

Role of excited electronic states in the high-pressure amorphization of benzene

High-pressure photodissociation of water as a tool for hydrogen synthesis and fundamental chemistry

The role of high-pressure in the reactivity of simple molecules: implications in prebiotic chemistry

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