High Pressure Photoinduced Ring Opening of Benzene

Ciabini, Lucia; Santoro, Mario; Bini, Roberto; Schettino, Vincenzo

doi:10.1103/physrevlett.88.085505

Cited by 119 publications

(119 citation statements)

References 22 publications

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“…The pressure shift of the exciton band is shown in Fig. 3 Upper, together with the data relative to the S 0 3 S 1 transition from the OP absorption spectra (21). The discrepancy between the two sets of data is large (Ϸ1 eV at 14 GPa) and is attributed to the method used to estimate the energy gap in the saturated OP absorption spectra.…”

Section: Resultsmentioning

confidence: 99%

“…The threshold pressure for activating the reaction is considerably lowered when the crystal is irradiated by laser light of suitable energy (21), which suggests the active role of excited states in the reaction. One open and intriguing question is how these findings are linked to recent results showing the existence of a critical intermolecular C-C distance used to induce the reaction in crystalline benzene (13), which implies that the microscopic mechanism of pressure-induced reactivity can be modeled only once the role of the excited states is fully understood.…”

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confidence: 99%

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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: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

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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“…Combining the data from X-ray diffraction at room temperature as a function of pressure, and an estimate of the amplitude of thermal motion as a function of temperature, it has been shown that all the points on the stability line correspond to the same instantaneous minimum distance between nearest neighbors along the a axis, which is also the calculated critical distance for the formation of a dimer, as shown in figure 1 which is the seed for the reaction initiation [8]. The most interesting aspect, in view of understanding and exploiting photochemistry, is that irradiation with light at λ ≤ 514 nm induces the same reaction at 16 GPa, very far from the critical structural and dynamical conditions to achieve the reactive approach of two neighbor molecules [9]. TP excitation profiles in the region 550-450 nm were measured up to 12 GPa.…”

Section: Benzene: Reactivity Triggered By Formation Of Dimersmentioning

confidence: 99%

“…When the reaction is performed starting from the pure, thermally annealed monoclic phase II, the reaction threshold [8]. Blue dots indicate the experimental threshold point for spontaneous transformation into amorphous hydrogenated carbon, the green dot indicates the threshold pressure at room temperature at which the same transformation can be induced by photoactivation with light at λ ≤ 514 nm [9]. (b) unit cell of the P2 1 /c crystal structure of benzene (phase II).…”

Section: Benzene: Reactivity Triggered By Formation Of Dimersmentioning

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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High Pressure Photoinduced Ring Opening of Benzene

Cited by 119 publications

References 22 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

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

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