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1.
Chemphyschem ; 2020 May 12.
Artigo em Inglês | MEDLINE | ID: mdl-32400097

RESUMO

Photochromic dimethyldihydropyrenes substituted with electron-withdrawing pyridinium groups have shown an increase of photo-induced ring-opening efficiency and a light sensitivity that is red shifted relative to the unsubstituted compound. However, a recently synthesized tetrapyridinium derivative showed a considerable decrease of the photo-isomerization quantum yield relative to the monopyridinium and bispyridinium derivatives. We provide a rationale for this unexpected photochemical behavior based on the comparative theoretical investigations of the relevant excited states of these systems. In particular, we found that the nature and order of the lowest two excited states depend on the number of pyridinium groups and on the symmetry of the system. While the lowest S1 excited state is photo-active in the monopyridinium and bispyridinium derivatives, the photo-isomerizing state is S2 in the reference unsubstituted compound and both S1 and S2 lead to isomerization in the tetrapyridinium derivative, albeit with a low efficiency. In the latter derivative, the photo-isomerization is hindered by the particular S1 /S2 conical intersection topology.

2.
Chemistry ; 2020 Mar 27.
Artigo em Inglês | MEDLINE | ID: mdl-32220098

RESUMO

A pyridinium substituted dithienylethene derivative was used for the first time as an efficient photo-reducing agent of two different substrates. This reaction exhibits high catalytic yields due to the continuous regeneration of the initial state of the photochromic molecule.

3.
J Phys Chem Lett ; 11(7): 2682-2688, 2020 Apr 02.
Artigo em Inglês | MEDLINE | ID: mdl-32182072

RESUMO

Two photoswitchable compounds that can operate under visible light irradiation are prepared and investigated using spectroscopic and computational studies. These all-visible systems are based on the dimethyldihydropyrene (DHP)/cyclophanediene (CPD) photochromic couple connected either to a bipyridine (bpy) unit or to a (tris(bpy)ruthenium(II)) complex through a pyridinium bridge. In these compounds, the DHP to CPD isomerization and the reverse CPD to DHP conversion can be triggered by illumination with red (>630 nm) and blue (460 nm) lights, respectively. The unambiguous and reversible response of these systems triggered by visible light make them potential candidates for biological purposes and electronic devices.

4.
Chemistry ; 25(6): 1573-1580, 2019 Jan 28.
Artigo em Inglês | MEDLINE | ID: mdl-30428127

RESUMO

A dynamic supramolecular approach is developed to promote the π-dimerization of viologen radicals at room temperature and in standard concentration ranges. The approach involves cis- or trans-protected palladium centers serving as inorganic hinges linking two functionalized viologens endowed with metal-ion coordinating properties. Based on detailed spectroscopic, electrochemical and computational data, we show that the one-electron electrochemical reduction of the viologen units in different dynamic metal/ligand mixtures leads to the formation of the same intramolecular π-dimer, regardless of the initial environment around the metallic precursor and of the relative ratio between metal and ligand initially introduced in solution. The large-scale electron-triggered reorganization of the building blocks introduced in solution thus involves drastic changes in the stoichiometry and stereochemistry of the palladium/viologen complexes proceeding in some cases through a palladium centered trans→cis isomerization of the coordinated ligands.

5.
Chemistry ; 24(49): 12961-12969, 2018 Sep 03.
Artigo em Inglês | MEDLINE | ID: mdl-29907986

RESUMO

We report the study of stimuli-responsive ZnII and FeII coordination polymers (MC34+ or MC24+ with M=Fe2+ or Zn2+ ). These soluble metallopolymers were formed spontaneously by reaction of an organic ligand (C34+ or C24+ ) with one molar equivalent of metal ions. The C34+ and C24+ ligands incorporate two chelating terpyridine groups bridged by a redox responsive hinge featuring two viologen units (viologen=N,N'-dialkyl-4,4'-bipyridinium) linked either with propyl (C34+ ) or ethyl (C24+ ) chains. The viologen units in the polymer chains were reduced (1 e- per viologen group) either by bulk electrolysis or by visible-light irradiation carried out in the presence of a photosensitizer. The 1 e- reduction of the viologen units in the MC24+ polymers induced a slight decrease in the viscosity of the solutions due to a modification of the overall charge carried by the metallopolymers. In strong contrast, reduction of coordination polymers involving propyl linkers (MC34+ ) led to a remarkable increase (≈+400 %) in observed viscosity. This reversible effect was attributed to a folding of the polymer chains triggered by π-dimerization of the photo-generated viologen cation radicals.

6.
Inorg Chem ; 56(8): 4357-4368, 2017 Apr 17.
Artigo em Inglês | MEDLINE | ID: mdl-28368594

RESUMO

Terpyridine ruthenium complexes linked to the dimethyldihydropyrene (DHP) photochromic unit have been synthesized and fully characterized by cyclic voltammetry and absorption and emission spectroscopy. The study of the photoisomerization reaction undergone by the DHP motif under visible light irradiation is reported. In comparison to previous work, the introduction of an electron-withdrawing pyridinium spacer between the chelating terpyridine unit and the DHP skeleton has considerably tuned the photochromic properties of the free ligands and their corresponding complexes in term of time response and photoreversibility. A rapid, reversible, and complete conversion between the closed and the open forms has been clearly evidenced under visible light irradiation. Only slight perturbations have been induced by the presence of ruthenium centers. Experimental findings and their interpretation have been supported by theoretical calculations.

7.
Adv Mater ; 29(18)2017 May.
Artigo em Inglês | MEDLINE | ID: mdl-28306176

RESUMO

Carbon nanotube-chromophore hybrids are promising building blocks in order to obtain a controlled electro-optical transduction effect at the single nano-object level. In this work, a strong spectral selectivity of the electronic and the phononic response of a chromophore-coated single nanotube transistor is observed for which standard photogating cannot account. This paper investigates how light irradiation strongly modifies the coupling between molecules and nanotube within the hybrid by means of combined Raman diffusion and electron transport measurements. Moreover, a nonconventional Raman enhancement effect is observed when light irradiation is on the absorption range of the grafted molecule. Finally, this paper shows how the dynamics of single electron tunneling in the device at low temperature is strongly modified by molecular photoexcitation. Both effects will be discussed in terms of photoinduced excitons coupled to electronic levels.

8.
Chemphyschem ; 18(7): 796-803, 2017 Apr 05.
Artigo em Inglês | MEDLINE | ID: mdl-28052477

RESUMO

The ability of three bis-viologen cyclophanes to act as redox-triggered contractile switches is investigated. Odd/even effects in the formation of cyclic bis-viologens are circumvented by the use of a Zincke salt intermediate and a tetrathiafulvalene template to prepare a flexible cyclophane with hexyl linkers. Comparative spectro-electrochemical studies of this macrocycle with two other pentyl- or heptyl-linked cyclic bis-viologens show that the development of intramolecular interactions in aqueous solution depends on the length of the bridges. This dependence is confirmed by EPR and DFT studies of the magnetic coupling in the diradical dication species. The anti-ferromagnetic or ferromagnetic nature of the coupling depend, respectively, on the odd or even number of methylene groups in the spacer.

9.
J Am Chem Soc ; 138(46): 15234-15242, 2016 11 23.
Artigo em Inglês | MEDLINE | ID: mdl-27766847

RESUMO

Viologen-centered electron transfer is used to trigger a complete dissociation of a porphyrin-based supramolecular architecture. In the oxidized state, self-assembly is induced by iterative association of individual porphyrin-based tectons. Dissociation of the self-assembled species is actuated upon changing the redox state of the bipyridium units involved in the tectons from their dicationic state to their radical cation state, the driving force of the disassembling process being the formation of an intramolecularly locked conformation partly stabilized by π-dimerization of both viologen cation radicals.

10.
Dalton Trans ; 45(35): 13700-8, 2016 Sep 21.
Artigo em Inglês | MEDLINE | ID: mdl-27264501

RESUMO

A series of dimethyldihydropyrene-appended metal complexes has been synthesized and thoroughly characterized using electrochemical and spectroscopic methods. The ring-opening reaction undergone by the dimethyldihydropyrene core under visible light irradiation proceeds much more efficiently when the metal complexes and the photochromic moiety are connected through a pyridinium-bridge vs a phenyl bridge. The clean electrochemical and photochemical responses of these hybrid systems make them good candidates for the conception of new multi-addressable photo- and redox-switches.

11.
Chem Commun (Camb) ; 51(78): 14682, 2015 Oct 07.
Artigo em Inglês | MEDLINE | ID: mdl-26340694

RESUMO

Correction for 'Reactivity of a pyridinium-substituted dimethyldihydropyrene switch under aerobic conditions: self-sensitized photo-oxygenation and thermal release of singlet oxygen' by Saioa Cobo et al., Chem. Commun., 2015, 51, 13886-13889.

12.
Chem Commun (Camb) ; 51(73): 13886-9, 2015 Sep 21.
Artigo em Inglês | MEDLINE | ID: mdl-26214006

RESUMO

The behavior of a pyridinium-substituted dimethyldihydropyrene photo-switch under aerobic conditions was investigated. During irradiation with red light (λ ≥ 630 nm), this compound plays the role of oxygen sensitizer and is quantitatively converted into an endoperoxide derivative. The photo-produced endoperoxide then thermally releases singlet oxygen to regenerate the starting compound.

13.
Chemistry ; 21(1): 455-67, 2015 Jan 02.
Artigo em Inglês | MEDLINE | ID: mdl-25358895

RESUMO

A series of photochromic derivatives based on the trans-10b,10c-dimethyl-10b,10c-dihydropyrene (DHP, "closed form") skeleton has been synthesized and their photoisomerization leading to the corresponding cyclophanediene (CPD, "open form") isomers has been investigated by UV/Vis and (1) H NMR spectroscopies. Substitution of the DHP core with electron-withdrawing pyridinium groups was found to have major effects on the photoisomerization efficiency, the most remarkable examples being to enhance the quantum yield of the opening reaction and to allow fast and quantitative conversions at much lower radiant energies. This effect was rationalized by theoretical calculations. We also show that the reverse reaction, that is, going from the open form to the closed form, can be electrochemically triggered by oxidation of the CPD unit and that the photo-opening properties of pyridine-substituted DHPs can be efficiently tuned by protonation, the system behaving as a multi-addressable molecular switch. These multi-addressable photochromes show promise for the development of responsive materials.

14.
J Am Chem Soc ; 135(16): 5974-7, 2013 Apr 24.
Artigo em Inglês | MEDLINE | ID: mdl-23574365

RESUMO

The conductance properties of a photoswitchable dimethyldihydropyrene (DHP) derivative have been investigated for the first time in single-molecule junctions using the mechanically controllable break junction technique. We demonstrate that the reversible structure changes induced by isomerization of a single bispyridine-substituted DHP molecule are correlated with a large drop of the conductance value. We found a very high ON/OFF ratio (>10(4)) and an excellent reversibility of conductance switching.

15.
Phys Chem Chem Phys ; 14(38): 13224-32, 2012 Oct 14.
Artigo em Inglês | MEDLINE | ID: mdl-22911106

RESUMO

This work reports a facile and cost-effective method for synthesizing photoactive α-Fe(2)O(3) films as well as their performances when used as photoanodes for water oxidation. Transparent α-Fe(2)O(3) mesoporous films were fabricated by template-directed sol-gel chemistry coupled with the dip-coating approach, followed by annealing at various temperatures from 350 °C to 750 °C in air. α-Fe(2)O(3) films were characterized by X-ray diffraction, XPS, FE-SEM and electrochemical measurements. The photoelectrochemical performance of α-Fe(2)O(3) photoanodes was characterized and optimized through the deposition of Co-based co-catalysts via different methods (impregnation, electro-deposition and photo-electro-deposition). Interestingly, the resulting hematite films heat-treated at relatively low temperature (500 °C), and therefore devoid of any extrinsic dopant, achieve light-driven water oxidation under near-to-neutral (pH = 8) aqueous conditions after decoration with a Co catalyst. The onset potential is 0.75 V vs. the reversible hydrogen electrode (RHE), thus corresponding to 450 mV light-induced underpotential, although modest photocurrent density values (40 µA cm(-2)) are obtained below 1.23 V vs. RHE. These new materials with a very large interfacial area in contact with the electrolyte and allowing for a high loading of water oxidation catalysts open new avenues for the optimization of photo-electrochemical water splitting.

16.
Nat Mater ; 11(9): 802-7, 2012 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-22863815

RESUMO

The future of energy supply depends on innovative breakthroughs regarding the design of cheap, sustainable and efficient systems for the conversion and storage of renewable energy sources. The production of hydrogen through water splitting seems a promising and appealing solution. We found that a robust nanoparticulate electrocatalytic material, H(2)-CoCat, can be electrochemically prepared from cobalt salts in a phosphate buffer. This material consists of metallic cobalt coated with a cobalt-oxo/hydroxo-phosphate layer in contact with the electrolyte and mediates H(2) evolution from neutral aqueous buffer at modest overpotentials. Remarkably, it can be converted on anodic equilibration into the previously described amorphous cobalt oxide film (O(2)-CoCat or CoPi) catalysing O(2) evolution. The switch between the two catalytic forms is fully reversible and corresponds to a local interconversion between two morphologies and compositions at the surface of the electrode. After deposition, the noble-metal-free coating thus functions as a robust, bifunctional and switchable catalyst.

17.
J Nanosci Nanotechnol ; 10(8): 5042-50, 2010 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-21125848

RESUMO

We present a new approach for patterning thin films of Prussian blue at the micro- and nano-metric scales. In a first step, a resist was deposited on a gold surface and patterns were generated by photolithography or electron beam lithography. The Prussian blue with idealized formula of KFe(III)[Fe(II)(CN)6] was deposited through the sequential exposure of the patterned surface to a series of solutions containing alternately absorbable Fe3+ cations and [Fe(CN)6]4- anions. These building blocks are gradually associated into dense and continuous films and patterned structures of Prussian blue can be obtained finally by lift-off. This approach was also used to deposit Prussian blue thin films on interdigitated nanoelectrodes and the current-voltage characteristics of this device were investigated.


Assuntos
Ferrocianetos/química , Nanoestruturas/química , Nanotecnologia/métodos , Condutividade Elétrica , Eletroquímica , Microscopia de Força Atômica , Microscopia Eletrônica de Varredura , Nanoestruturas/ultraestrutura , Propriedades de Superfície
18.
J Am Chem Soc ; 131(41): 15049-54, 2009 Oct 21.
Artigo em Inglês | MEDLINE | ID: mdl-19788300

RESUMO

Much research has been directed toward the development of electrically switchable optical materials for applications in memory and display devices. Here we present experimental evidence for an electric-field-induced charge-transfer phase transition in two cyanometalate complexes: Rb(0.8)Mn[Fe(CN)(6)](0.93).1.62H(2)O and Co(3)[W(CN)(8)](2)(pyrimidine)(4).6H(2)O, involving changes in their magnetic, optical, and electronic properties as well. Application of an electric field above a threshold value and within the thermal hysteresis region leads to a transition from the high- to the low-temperature phase in these compounds. A model is proposed to explain the main observations on the basis of a para-ferroelectric transition. Our observations suggest that this new concept of electrical switching, based on materials exhibiting charge-transfer phase transitions with large thermal hysteresis loops, may open up doors for novel electro-optical devices.

19.
Phys Chem Chem Phys ; 10(38): 5882-9, 2008 Oct 14.
Artigo em Inglês | MEDLINE | ID: mdl-18818842

RESUMO

A series of thin films of Prussian blue analogues is investigated by X-ray absorption spectroscopy (XAS) at the Fe, Co and Mn L(2,3)-edges. The ligand field multiplet theory enables us to examine accurately the electronic structure of these materials. Experimental XAS spectra of CoFe Prussian blue analogues are successfully reproduced using a ground state configuration including metal-to-ligand (MLCT) and ligand-to-metal charge transfer (LMCT) at the Co and Fe L(2,3)-edges. In particular, a huge improvement is achieved for satellite peaks at the Co(iii) L(2,3)-edges compared to previous calculations in the literature based on LMCT effects only. On the other hand, XAS spectra of MnFe analogues synthesized for the first time, can be reproduced conveniently by taking into account either MLCT or LMCT depending on the conditions of the sample preparation. For each thin film, the proportion of the different oxidation states of Co, Fe and Mn is evaluated. Unexpectedly, this analysis reveals the presence of a significant amount of a reduced phase, which turns out to be strongly dependent on the sample synthesis and storage conditions.

20.
J Am Chem Soc ; 130(28): 9019-24, 2008 Jul 16.
Artigo em Inglês | MEDLINE | ID: mdl-18570417

RESUMO

Single crystals of the {Fe (II)(pyrazine)[Pt(CN) 4]} spin crossover complex were synthesized by a slow diffusion method. The crystals exhibit a thermal spin transition around room temperature (298 K), which is accompanied by a 14 K wide hysteresis loop. X-ray single-crystal analysis confirms that this compound crystallizes in the tetragonal P4/ mmm space group in both spin states. Within the thermal hysteresis region a complete bidirectional photoconversion was induced between the two phases (high spin right arrow over left arrow low spin) when a short single laser pulse (4 ns, 532 nm) was shined on the sample.

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