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1.
Dalton Trans ; 2020 Feb 27.
Artigo em Inglês | MEDLINE | ID: mdl-32103210

RESUMO

Two mononuclear Ru(ii) complexes, i.e. [RuCl(κ3N-terpy)(κ2N-dpp)]PF6 ([1]PF6; terpy = 2,2':6',2''-terpyridine; dpp = 2,3-bis(2'-pyridyl-pyrazine) and [RuCl(κ3N-tpm)(κ2N-dpp)]Cl ([2]Cl; tpm = tris(1-pyrazolyl)methane), and one dinuclear complex, i.e. [Ru2Cl(κ3N-tpm)(µ-κ2N:κ2N-dpp)Ru(κ2N-bpy)2][PF6]3 ([3][PF6]3; bpy = 2,2'-bipyridine), have been synthesized and their water oxidation catalytic properties have been investigated. A combined DFT and experimental (35Cl NMR and conductivity measurements) study aimed to elucidate the nature of [1]+ and [2]+ in aqueous solution has also been performed, indicating that one water molecule is allowed to enter the first coordination sphere of [2]+ in the ground state, replacing one tpm nitrogen. Conversely, in the case of [1]+, water coordination, assumed to be needed for the water oxidation process, presumably occurs following the oxidation of the metal. For all complexes, a catalytic wave has been detected in acetonitrile/water 1 : 1 (v/v) solution in the range 1.4-1.7 V vs. SCE. In all cases, water oxidation (investigated at pH < 8) takes place initially via a proton-coupled two-electron, two-proton process with the formation of an Ru(iv)[double bond, length as m-dash]O moiety, followed by one electron oxidation and water nucleophilic attack. The TON and TOF values (within the range of 16-33 and 1.3-2.2 h-1, respectively) of the complexes are higher than those of the benchmark [Ru(LLL)(LL)(OH2)]2+-type species (LLL and LL are tridentate and bidentate polypyridine ligands, respectively), which is [Ru(terpy)(bpm)(OH2)]2+.

2.
Photochem Photobiol Sci ; 19(1): 105-113, 2020 Jan 22.
Artigo em Inglês | MEDLINE | ID: mdl-31930262

RESUMO

We report on the light-switch behaviour of two head-to-tail expanded bipyridinium species as a function of their interaction with calf thymus DNA and polynucleotides. In particular, both DNA and polynucleotides containing exclusively adenine or guanine moieties quench the luminescence of the fused expanded bipyridinium species. This behaviour has been rationalized demonstrating that a reductive photoinduced electron transfer process takes place involving both adenine or guanine moieties. The charge separated state so produced recombines in the tens of picoseconds. These results could help in designing new organic substrates for application in DNA probing technology and lab on chip-based sensing systems.


Assuntos
Sondas de DNA/química , DNA/análise , Corantes Fluorescentes/química , Imagem Óptica , Compostos de Piridínio/química , Animais , Bovinos , Sondas de DNA/síntese química , Corantes Fluorescentes/síntese química , Estrutura Molecular , Oxirredução , Compostos de Piridínio/síntese química , Espectroscopia de Luz Próxima ao Infravermelho , Raios Ultravioleta
3.
Inorg Chem ; 58(9): 5807-5817, 2019 May 06.
Artigo em Inglês | MEDLINE | ID: mdl-31017774

RESUMO

Three new linearly arranged bichromophoric systems 1-3 have been prepared, and their photophysical properties have been studied, taking also advantage of femtosecond pump-probe transient absorption spectroscopy. The three compounds contain the same chromophores, that is a Ru(II)-terpy-like species and a fused expanded bipyridinium (FEBP) unit, separated by three different, variously methylated biphenylene-type bridges. The chromophores have been selected to be selectively addressable, and excitation involving the Ru-based or the FEBP-based dyes results in different excited-state decays. Upon Ru-based excitation at 570 nm, oxidative photoinduced electron transfer (OPET) takes place in 1-3 from the 3MLCT state; however, the charge-separated species does not accumulate, indicating that the charge recombination rate constant exceeds the OPET rate constant. Upon excitation of the organic dye at 400 nm, the FEBP-based 1π-π* level is prepared, which undergoes a series of intercomponent decay events, including (i) electron-exchange energy transfer leading to the MLCT manifold (SS-EnT), which successively decays according to 570 nm excitation, and (ii) reductive photoinduced electron transfer (RPET), leading to the preparation of the charge-separated (CS) state. Reductive PET, involving the FEBP-based singlet state, is much faster than oxidative PET, involving the MLCT triplet state, essentially because of driving force reasons. The rate constant of CR is intermediate between the rate constants of OPET and RPET, and this makes 1-3 capable to selectively read the 400 nm excitation as an active input to prepare the CS state, whereas excitation at wavelengths longer than 480 nm is inefficient to accumulate the CS state. Moreover, intriguing differences between the rate constants of the various processes in 1-3 have been analyzed and interpreted according to the superexchange theory for electron transfer. This allowed us to uncover the role of the electron-transfer and hole-transfer superexchange pathways in promoting the various intercomponent photoinduced decay processes occurring in 1-3.

4.
Photochem Photobiol Sci ; 18(9): 2164-2173, 2019 Sep 11.
Artigo em Inglês | MEDLINE | ID: mdl-30793142

RESUMO

The early photophysical events occurring in the dinuclear metal complex [(ttb-terpy)(I)Ru(µ-dntpz)Ru(bpy)2]3+ (2; ttb-terpy = 4,4',4''-tri-tert-butyl-terpy; bpy = 2,2'-bipyridine; dntpz = 2,5-di-(1,8-dinaphthyrid-2-yl)pyrazine) - a species containing the chromophoric {(bpy)2Ru(µ-dntpz)}2+ subunit and the catalytic {(I)(ttb-terpy)Ru(µ-dntpz)}+ unit, already reported to be able to perform photocatalytic water oxidation - have been studied by ultrafast pump-probe spectroscopy in acetonitrile solution. The model species [Ru(bpy)2(dntpz)]2+ (1), [(bpy)2Ru(µ-dntpz)Ru(bpy)2]4+ (3), and [(ttb-terpy)(I)Ru((µ-dntpz)Ru[(ttb-terpy)(I)]2+ (4) have also been studied. For completeness, the absorption spectra, redox behavior of 1-4 and the spectroelectrochemistry of the dinuclear species 2-4 have been investigated. The usual 3MLCT (metal-to-ligand charge transfer) decay, characterized by relatively long lifetimes on the ns timescale, takes place in 1 and 3, whose lowest-energy level involves a {(bpy)2Ru(dntpz)}2+ unit, whereas for 2 and 4, whose lowest-energy excited state involves a 3MLCT centered on the {(I)(ttb-terpy)Ru(µ-dntpz)}+ subunit, the excited-state lifetimes are on the ps timescale, possibly involving population of a low-lying 3MC (metal-centered) level. Compound 2 also exhibits a fast process, with a time constant of 170 fs, which is attributed to intercomponent energy transfer from the MLCT state centered in the {(bpy)2Ru(µ-dntpz)}2+ unit to the MLCT state involving the {(I)(ttb-terpy)Ru(µ-dntpz)}+ unit. Both the intercomponent energy transfer and the MLCT-to-MC activation process take place from non-equilibrated MLCT states.

5.
Dalton Trans ; 47(13): 4733-4738, 2018 Mar 26.
Artigo em Inglês | MEDLINE | ID: mdl-29537424

RESUMO

We prepared a bichromophoric species 1, made of two different bodipy dyes bridged by a d-galactose unit. 1 exhibits different emission spectra when located in different compartments of biological systems, independently of its concentration. This is an unprecedented feature for a single multicomponent molecule and is due to the dependence on the environment of the photoinduced energy transfer process occurring between its bodipy subunits. Therefore, 1 can give useful information about cell composition and ultimately anomalies without requiring the simultaneous use of several different compounds, paving the way for the use of environment-controlled inter-component energy transfer to gain cell information based on luminescence imaging.

6.
Inorg Chem ; 57(4): 2175-2183, 2018 Feb 19.
Artigo em Inglês | MEDLINE | ID: mdl-29394056

RESUMO

The paper reports an unprecedented spectrophotometric determination of amines in chloroform, in which amines are not transformed into colored derivatives. This result has been achieved by exploiting the acid-base properties of the tight-ion-paired metal complexes [(HR2DTO)Pt(H2R2DTO)][Cl], which are able to donate a HCl molecule to an amine, giving rise to an ammonium salt and to the neutral complexes [(HR2DTO)2Pt]. The circumstance that [(HR2DTO)Pt(H2R2DTO)][Cl] and [(HR2DTO)2Pt] species show different absorptions in the visible region of the electromagnetic spectrum enables the aforementioned platinum complexes to behave as self-indicating titrants in the spectrophotometric determination of aliphatic amines, which are known to be UV-vis transparent. The new method has been tested by determining a series of fatty amines in the bulk and gave excellent results. The limits of applicability of this method (pKa > 4) were found by testing a series of benzodiazepines.


Assuntos
Clorofórmio/química , Ácido Clorídrico/química , Compostos Organoplatínicos/química , Aminas/química , Estrutura Molecular
7.
Chemistry ; 23(65): 16497-16504, 2017 Nov 21.
Artigo em Inglês | MEDLINE | ID: mdl-28922481

RESUMO

Self-assembly is a powerful synthetic tool that has led to the development of one-, two- and three-dimensional architectures. From MOFs to molecular flasks, self-assembled materials have proven to be of great interest to the scientific community. Here we describe a strategy for the construction and de-construction of a supramolecular structure through unprecedented photo-induced assembly and dis-assembly. The combination of two approaches, a [n×1]-directional bonding strategy and a ligand photo-dissociation strategy, allows the photo-induced assembly of a polypyridyl RuII precursor into a discrete molecular square. Diffusion-ordered NMR spectroscopy confirmed the synthesis of a higher volume species, while the identity of the species was established by high-resolution mass spectrometry and single-crystal X-ray diffraction studies. The self-assembled square is not obtained by classical thermal techniques in similar conditions, but is obtained only by light-irradiation. The tetraruthenium square has an excited-state lifetime (135 ns), 40 times that of its mononuclear precursor and its luminescence quantum yield (1.0 %) is three orders of magnitude higher. These remarkable luminescence properties are closely related to the relatively rigid square structure of the tetraruthenium assembly, as suggested by slow radiationless decay and transient absorption spectroscopy. The results described herein are a rare example of photo-induced assembly and dis-assembly processes, and can open the way to a new avenue in supramolecular chemistry, leading to the preparation of structurally organized supermolecules by photochemical techniques.

9.
Phys Chem Chem Phys ; 19(21): 14055-14065, 2017 May 31.
Artigo em Inglês | MEDLINE | ID: mdl-28518200

RESUMO

Herein, the synthesis and the photophysical and redox properties of a new perylene bisimide (PBI) species (L), bearing two 1,10-phenanthroline (phen) ligands at the two imide positions of the PBI, and its dinuclear Ru(ii) and Os(ii) complexes, [(bpy)2Ru(µ-L)Ru(bpy)2](PF6)4 (Ru2; bpy = 2,2'-bipyridine) and [(Me2-bpy)2Os(µ-L)Os(Me2-bpy)2](PF6)4 (Os2; Me2-bpy = (4,4'-dimethyl)-2,2'-bipyridine), are reported. The absorption spectra of the compounds are dominated by the structured bands of the PBI subunit due to the lowest-energy spin-allowed π-π* transition. The spin-allowed MLCT transitions in Ru2 and Os2 are inferred by the absorption at 350-470 nm, where the PBI absorption is negligible. The absorption band extends towards the red region for Os2 due to the spin-forbidden MLCT transitions, intensified by the heavy osmium center. The reduction processes of the compounds are dominated by two successive mono-electronic PBI-based processes, which in the metal complexes are slightly shifted compared to the free ligand. On oxidation, both metal complexes undergo an apparent bi-electronic process (at 1.31 V vs. SCE for Ru2 and 0.77 V for Os2), attributed to the simultaneous one-electron oxidation of the two weakly-interacting metal centers. In Ru2 and Os2, the intense fluorescence of L subunit (λmax, 535 nm; τ, 4.3 ns; Φ, 0.91) is fully quenched, mainly by photoinduced electron transfer from the metal centers, on the ps timescale (time constant, 11 ps in Ru2 and 3 ps in Os2). Such photoinduced electron transfer leads to the formation of a charge-separated state, which directly decays to the ground state in about 70 ps in Os2, but produces the triplet π-π* state of the PBI subunit in 35 ps in Ru2. The results provide information on the excited-state processes of the hybrid species combining two dominant classes of chromophore/luminophore species, the PBI and the metal polypyridine complexes, and can be used for future design on new hybrid species with made-to-order properties.

10.
Dalton Trans ; 45(48): 19238-19241, 2016 Dec 06.
Artigo em Inglês | MEDLINE | ID: mdl-27878152

RESUMO

The novel dendritic-shaped, heptanuclear compound 1 - the first mixed Os-Ru dendrimer with tris-chelating bridging ligands - has been synthesized and its photophysics studied by fs pump-probe transient spectroscopy. In 1, all light energy absorbed by six identical Ru(ii) chromophores is funnelled to the luminescent central Os(ii) core, with a time constant of 11 ps, by Dexter energy transfer.

11.
Dalton Trans ; 45(36): 14109-23, 2016 Sep 28.
Artigo em Inglês | MEDLINE | ID: mdl-27537828

RESUMO

The charge transfer dynamics involving a new Ru(ii) polypyridine complex (1), developed to generate highly oxidizing photoholes for water oxidation, was studied by electrochemical, photoelectrochemical and spectroscopic means. Mesoporous TiO2 electrodes sensitized with complex 1, under 1 sun illumination (420 nm cut-off filter) and a moderate applied bias (0.3 V vs. SCE), in ACN/0.1 M LiI as a sacrificial electron donor reach an anodic photocurrent of ∼0.2 mA cm(-2) with 3% photon-to-current conversion efficiency. When 0.1 M aqueous sodium ascorbate (pH 3) is used instead of iodide, the photocurrent increases to ∼0.7 mA cm(-2) and up to 1 mA cm(-2) if the concentration of ascorbate is increased to 0.5 M, explainable with a modification of the charge injection mechanism. This is the photoelectrochemical evidence, in the heterogeneous phase, of the so-called "anti-biomimetic" pathway, confirmed in transient absorption spectroscopy by a long lived sharp bleaching at 480 nm and a narrow absorption between 500 and 550 nm, characteristic fingerprints of the photogenerated reduced state (1(-)). After the formation of *1/TiO2, reductive quenching by ascorbate occurs, not observed in LiI where the classic oxidative quenching takes place. Due to the modest excited state oxidation potential, electron transfer to TiO2 is thermodynamically more favorable from 1(-) than *1. Lastly, experiments performed with sensitized SnO2 photoanodes, where *1 undergoes the usual oxidative quenching, by charge transfer to the conduction band of the metal oxide allowed us to verify the interaction between 1(+) and IrO2 nanoparticles, grafted onto the surface in order to drive photoinduced water oxidation.

16.
Chemphyschem ; 16(15): 3147-50, 2015 Oct 26.
Artigo em Inglês | MEDLINE | ID: mdl-26331881

RESUMO

The first donor-acceptor species in which a strongly emissive N-annulated perylene dye is connected to a methylviologen electron acceptor unit via its macrocyclic nitrogen atom, is prepared by a stepwise, modular procedure. The absorption spectra, redox behavior, spectroelectrochemistry and photophysical properties of this dyad and of its model species are investigated, also by pump-probe fs transient absorption spectroscopy. Photoinduced oxidative electron transfer from the excited state of the dyad, centered on the N-annulated perylene subunit, to the appended methyviologen electron acceptor takes place in a few ps. The charge-separated species recombines in 19 ps. Our results indicate that N-annulated perylene can be connected to functional units by taking advantage of the macrocyclic nitrogen, an option never used until now, without losing their properties, so opening the way to new designing approaches.

17.
Angew Chem Int Ed Engl ; 54(23): 6775-9, 2015 Jun 01.
Artigo em Inglês | MEDLINE | ID: mdl-25925409

RESUMO

A high-yielding synthesis of a series of polyimide dendrimers, including decacyclene- and perylene-containing dendrimer D6, in which two types of polyimide dyes are present, is reported. In these constructs, the branching unit is represented by trisphenylamine, and the solubilizing chains by N-9-heptadecanyl-substituted perylene diimides. The photophysical properties of the dendrimers have been studied by absorption, steady-state, and time-resolved emission spectroscopy and pump-probe transient absorption spectroscopy. Photoinduced charge-separated (CS) states are formed on the femtosecond timescale upon visible excitation. In particular, in D6, two different CS states can be formed, involving different subunits that decays independently with different lifetimes (ca. 10-100 ps).

18.
Photochem Photobiol Sci ; 14(5): 909-18, 2015 May.
Artigo em Inglês | MEDLINE | ID: mdl-25722091

RESUMO

A novel molecular dyad, 1, made of a dinuclear {[Re2(µ-X)2(CO)6(µ-pyridazine)]} component covalently-linked to a fullerene unit by a carbocyclic molecular bridge has been prepared and its redox, spectroscopic, and photophysical properties - including pump-probe transient absorption spectroscopy in the visible and near-infrared region - have been investigated, along with those of its model species. Photoinduced, intercomponent electron transfer occurs in 1 from the thermally-equilibrated, triplet metal/ligand-to-ligand charge-transfer ((3)MLLCT) state of the dinuclear rhenium(I) subunit to the fullerene acceptor, with a time constant of about 100 ps. The so-formed triplet charge-separated state recombines in a few nanoseconds by a spin-selective process yielding, rather than the ground state, the locally-excited, triplet fullerene state, which finally decays to the ground state by intersystem crossing in about 290 ns.


Assuntos
Elétrons , Fulerenos/química , Processos Fotoquímicos , Piridazinas/química , Rênio/química , Transferência de Energia , Estrutura Molecular , Oxirredução , Análise Espectral , Fatores de Tempo , Tolueno/química
19.
Dalton Trans ; 43(40): 14926-30, 2014 Oct 28.
Artigo em Inglês | MEDLINE | ID: mdl-25116513

RESUMO

A new tetracobalt(III) cubane 1, carrying functionalized peripheral ethynyl groups, was prepared. Cubane 1 catalyses photoinduced water oxidation, indicating that the ethynyl groups do not negatively affect the catalytic properties of the Co cubane assembly. In contrast, the quantum yield for water oxidation (0.36) is significantly increased with respect to the prototype, simplest species.

20.
Dalton Trans ; 43(47): 17647-58, 2014 Dec 21.
Artigo em Inglês | MEDLINE | ID: mdl-25055956

RESUMO

A Bodipy species bearing an acetyl-acetonate (acac) group, , has been prepared from a blue absorbing borondipyrromethene core bearing gallate substituted paraffin chains. Compound chelates a Pt(ii) center having an orthometalated 2-phenyl-pyridine anion (ppy) as an additional ligand, giving rise to a new bichromophoric Pt(ii)-Bodipy species, . The absorption spectra, redox behavior and photophysical properties of , and of the neutral Pt(ii) compound , containing ppy and an acac derivative as ligands, have been studied. Compounds and are used as models for the Bodipy-based and the metal-based subunits of , respectively. The (3)LC emission of is fully quenched in , whereas the Bodipy fluorescence is only weakly reduced in compared to , indicating weak interaction between the subunits. Two different charge-separated (CS) states have a role in the intercomponent excited state decays of . Notably, whereas in all the previously investigated bichromophoric metal(polypyridine)-Bodipy compounds, the light absorbed by the metal-based unit leads to population of the lowest-energy triplet Bodipy-based level, in it contributes with high efficiency (>99%) to the Bodipy fluorescence. An efficient and formally forbidden (3)LC to (1)Bodipy energy transfer occurring by Förster mechanism is, unprecedently, the dominant (3)LC decay process in .

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