1,721,130 research outputs found
Rationalizing the electronic properties of two classes of push–pull DSSC sensitizers based on Zn(II) di- or tetrarylporphyrinates substituted in meso or beta-pyrrolic positions: an electrochemical investigation
No full textPush–pull Zn(II)-porphyrinates have recently shown attracting performances as
light harvesting systems in dye-sensitized solar cells (DSSCs). To fully exploit their
intrinsically high efficiency it is important to finely tune their HOMO and LUMO levels,
which can be achieved by proper choice of the push and pull substituents. Of course
such target-oriented molecular design requires the availability of reliable relationships
between molecular structure and electronic properties; therefore we have carried out
a detailed electrochemical investigation, also supported by spectroscopy and
theoretical computations, on a wide, systematic range of Zn(II)-porphyrinates:
(a) a family of 5,15-meso substituted ones with phenylethynyl linkers, including a
first "benchmark" symmetric series carrying on the opposite terminals the same
substituent (N(CH3)2, OCH3, COOCH3, COOH, NO2); and a second push–pull one,
with the terminal positions carrying one donor and one acceptor group belonging to
the series above. Moreover, two suitably modified porphyrins allowed evaluation of
the effects of (i) the presence or absence of the phenyl group in the linker between
the porphyrin core and the acceptor group, and (ii) the effect of perfluorination on the
same phenyl group;
(b) a family of mono and, for the first time, disubstituted push-pull ZnIIporphyrinates
bearing a variety of ethynyl-phenyl moieties in β-pyrrolic position,
which were compared with their meso analogues, producing evidence that, although
the HOMO-LUMO energy gap of the meso substituted push-pull dyes is lower, the β
mono or disubstituted push-pull porphyrinic dyes show comparable or better
efficiencies when acting as sensitizers in DSSCs, possibly on account of a more
facile charge injection into TiO2.
A rationalization scheme is proposed concerning relationship between structure
and redox properties, affording inter alia interesting clues on the different localization
of the redox centres and the effective conjugation between the porphyrin core and
the side chains as a function of the molecular design.
References:
[1] P. R. Mussini, A. Orbelli Biroli, F. Tessore, M. Pizzotti, C. Biaggic, G. Di Carlo, M.
G. Lobello, F. De Angelis, Electrochimica Acta 85 (2012) 509– 523
[2] G. Di Carlo, A. Orbelli Biroli, M. Pizzotti, F. Tessore, V. Trifiletti, R. Ruffo, A.
Abbotto, A. Amat, F. De Angelis, P. R. Mussini, Chemistry-a European Journal, in
press (2013)
Electronic Structure and Reactivity of Dioxygen-Platinum Complexes: an ab Initio MO-LCAO Study
No full textAb initio Hartree Fock calculations have been carried out on the complex L2Pt(η2-O2) and its derivatives L2Pt-(OOH)X and L2Pt(OOH)(XY) obtained by reaction with HX (HX = H2O, HCl, HOOCH, NH3) and HXYH (HXYH = oxalic acid, o-catechol, hydrazine, hydroxylamine, ethylendiamine, o-phenylendiamine). In addition also the reaction L2Pt(OOH)X + HX → H2O2 + L2PtX2 leading to the formation of hydrogen peroxide has been studied. The theoretical investigation gave, for all considered species, optimum complex geometry, charge distribution and reaction energies being evaluated by means of a correlation energy density functional. The ability of the HX reagents to form hydrogen peroxide is discussed in terms of absolute acidity and coordinating capability of the X- groups. This allows interpretation of the more peculiar aspects of the chemical activation of dioxygen that leads to the coordinated hydroperoxide species or hydrogen peroxide
SYNTHESIS OF SOME BENZOTRIAZOLES BY DEOXYGENATION OF O-NITROPHENYLAZO COMPOUNDS BY TERTIARY-AMINES AND CO
No full textNEt3 promotes the deoxygenation of specific ortho-nitrophenylazo compounds affording benzotriazoles in good yields and selectivities. The role of the amine is examined in the deoxygenation process with CO as the final oxygen acceptor
Tailoring Transition Metal Complexes for Nonlinear Optics Applications. 2. A Theoretical Investigation of the Second-Order Nonlinear Optical Properties of M(CO)5L Complexes (M = Cr, W; L = Py, PyCHO, Pyz, PyzBF3, BPE, BPEBF3)
No full textThe authors report an ab initio study of 2nd-order nonlinear optical (NLO) properties and absorption electronic spectra of push-pull transition metal chromophores [M(CO)5L] (M = Cr, W; L = pyridine (Py), 4-formyl-pyridine (PyCHO), pyrazine (Pyz), trans-1,2-bis(4-pyridyl)ethylene (BPE)). Pyz and BPE are considered either with 1 N atom free or interacting with the strong acceptor BF3. All of the mol. properties were calcd. using 2 different and methodol. independent approaches: the time dependent and coupled perturbed d. functional theories (TDDFT and CPDFT) and the sum-over-states (SOS) approach, where the excited states are obtained via the single CI (SCI) ab initio method. DFT results are in acceptable agreement with the exptl. energy values of electronic transitions (with the exception of chromophores with the large greek p-delocalization, like BPE); SCI calcns. overestimate excitation energies and produce an inversion in the order of dM greek pi*L and dM greek p*CO transitions. The SCI-SOS approach gives 1st-order hyperpolarizabilities, basically in agreement as trend and values with the expts. and seems to be a tool generally suitable for the evaluation of these properties also for transition metal complexes. However, the 1st-order hyperpolarizabilities computed using the CPDFT approach are consistently overestimated in comparison with the exptl. results, esp. in the case of a ligand with large greek p-delocalization. Also the 2-level approxn. taking into account only the lowest energy charge transfer excitation (e.g., dM greek p*L) is not applicable to chromophores with the extended greek p-delocalized ligand (BPE) coordinated to a transition metal, due to significant contributions originating from intraligand greek pL greek p*L transitions. This study reports a detailed anal. and comparison of electronic NLO effects of transition metal complexes computed with DFT and ab initio SCI-SOS methodol
The reaction of molibdenum(VI) dioxo derivatives with hetrocumulenes
No full textThe reactions of ArNSO (Ar = p-MeC6H4) with cis-Mo(O)2(chel)2 (chel = S2CNEt2, CH3COCH- COCHH3) give the molybdenum(VI) oxo-arylimido derivatives, Mo(O)(NAr)(hel)2, and sulphur dioxide. From cis-Mo(O)2(S2CNEt2)2 and CyNCO (Cy = C6H11) the dimeric Mo2O3(S2CNEt2)4 is obtained, with the concomitant formation of carbon dioxide and biuret, (CyNHCO)2NCy. The spectroscopic properties of the molybdenum(VI) oxo-arylimido derivatives are reported and the possible reaction mechanisms are discussed
Reactions of amines with Pt(PPh3)2O2
No full textBy reaction of Pt(PPh3)2O2 with {A figure is presented} ethanol the complexes Pt(PPh3)2 {A figure is presented} (R = R′ = H; R = H, R′ = NO2; RR′ = {A figure is presented} obtained. The analogous derivatives isolated from Pt(PPh3)2O2 and the ortho-diamines with R = H, R′ = Me or R = R′= Me, showed some peculiar spectroscopic properties. A related reaction has been carried out with {A figure is presented} being isolated; the latter was also obtained from cis-Pt(PPh3)2Cl2 and {A figure is presented} in a basic medium. The platinum diamido complexes can be reversibly protonated with HBF4 to give [Pt(PPh3)2 {A figure is presented} (BF-4)2 H2O Attempted reactions of Pt(PPh3)2O2 with NH3, NH2CH2CH2NH2 an p-RC6H4NH2 (R = Me, OMe, NO2) did not give well characterizable products, while with But-NH2 an already known cluster complex was obtained
SURFACE ORGANOMETALLIC CHEMISTRY - THE SURFACE SPECIES [HOS3(CO)(10)(OSI)] AS A REACTIVE INTERMEDIATE IN THE SILICA-MEDIATED SYNTHESIS OF VARIOUS OSMIUM CARBONYL CLUSTERS STARTING FROM [OS-3(CO)(12)]
No full textDeoxygenation reaction of 2-nitrophenol. Synthesis and x-ray crystal structure of Ru(OC6H4NO-o)(CO)(PPh3)2
No full textBy reaction of [Ru(CO)3(PPh3)2] with 2-nitrophenol, the deep brown ruthenium(II) complex, [Ru(OC6H 4NO-o)(OC6H4NO2-o)(CO)(PPh 3)2], has been obtained. X-Ray crystallography has shown that the complex contains a o-nitrosophenolate ligand, which co-ordinates to ruthenium in a chelating fashion through its nitroso-nitrogen and phenolic oxygen atoms
Arylazo and aryldiimine derivatives of ruthenium
No full textThe reaction of (Ph3P)2Ru(CO)3 with (p-RC6H4N2)+(BF4-) (R = NO2, F, OMe, H) or (p-Me2NC6H4N2)+(BPh4-) gave arylazo complexes, [p-RC6H4N2Ru(CO)2(PPh3)2]+X-, which were protonated with HBF4 to give diimines [p-RC6H4N:NHRu(CO)2(PPh3)2]2+ (BF4-)2
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