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

Citroni, Mario; Bini, Roberto; Foggi, Paolo; Schettino, Vincenzo

doi:10.1073/pnas.0802269105

Cited by 59 publications

(70 citation statements)

References 34 publications

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“…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 and propagate a reaction (14). 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.…”

mentioning

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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mentioning

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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“…TP excitation profiles in the region 550-450 nm were measured up to 12 GPa. In this wavelength range we observe the symmetry forbidden TP transition from the ground state to S 1 ( 1 B 2u ), weakly allowed by vibronic coupling, and the red edge of higher energy transitions [10]. The main insight on the reaction mechanism comes from the fluorescence spectra.…”

Section: Benzene: Reactivity Triggered By Formation Of Dimersmentioning

confidence: 98%

“…However, if excimer emission is only possible at defects, its intensity is weaker and not reproducible in different experiments and mostly not reversible with pressure. In benzene, the relative intensities of monomer and excimer emission is reversible, except for a small hysteresis, if the experiment is made avoiding the irreversible chemical reaction [10], which is an evidence that the excimers are mainly formed in the bulk crystal.…”

Section: High-pressure Reactivity and Excimer Formationmentioning

confidence: 99%

Non-linear optical properties of molecular systems under high static pressures

Citroni

Fanetti

Foggi

et al. 2014

J. Phys.: Conf. Ser.

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Abstract.Applied static pressure can largely modify the structure and dynamics of molecular systems, with consequences on their optical properties and chemical stability. When photochemical effects are exploited in conjunction with the structural and dynamical conditions attained at high density, chemical reactivity may become highly selective and efficient, yielding technologically attractive products. Non-linear optical spectroscopies are a powerful tool to investigate molecular energetics and dynamics, and thus unveil key aspects of the chemical reactivity at a molecular level. Their application to high-pressure samples is experimentally challenging, mainly because of the small sample dimensions and the non-linear effects generated in the anvil materials. In this paper we review the main results on the behavior of electronic states at high pressure, obtained by non-linear optical techniques, discussing the relationship between pressure-induced structural modifications and chemical reactivity, and the state of the art of ongoing research.

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“…In fact, the excited molecule is generally characterized by a reduced binding order that determines the stretching of the molecular bonds, the lowering of rotational and torsional barriers and also a polarity increase possibly leading to dissociation and ionization. These excited molecules, or the excimeric species possibly formed can be particularly aggressive from a chemical point of view, and depending on their lifetime and free mean path, can trigger and propagate a reaction (Citroni et al 2008). These processes are extremely efficient in unsaturated hydrocarbons because they can be triggered by two-photon (TP) excitations realized with cw (continuous wave) low-power laser sources.…”

Section: Pressure-induced Reactivity In Molecular Systemsmentioning

confidence: 99%

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

Cited by 59 publications

References 34 publications

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

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

Non-linear optical properties of molecular systems under high static pressures

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

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