Paulina Dreyse

Electrochemical reduction of SO2 on poly-Co-3-tetraaminophenylporphyrin glassy carbon modified electrode¶

This article describes the electrochemical reduction of sulfite in water–ethanol mixtures under acidic conditions on a glassy carbon electrode modified with a conducting film formed by Co(II) tetra-3-aminophenyl porphyrin. Rotating disc electrode experiments show a kinetic limitation related with the formation of an adduct between the reduced porphyrin and the sulfur compound. UV–Visible spectroelectrochemical data suggest that Co(I) is not stabilized; thus the adduct should involve a radical species of the porphyrin. However, the resulting modified electrode is stable and shows a linear relationship between current and concentration of the sulfur species at pH 1. The detection range of sulfite by the modified electrode goes from 12 to 150 mg L−1. The detection limit is 4.15 mg L−1. ¶This article is dedicated to Professor A. Mederos.

ELECTROCHEMICAL REDUCTION OF NITRITE AT POLYMERIC Co (II)-TETRA-3-AMINO-PHENYL-PORPHYRIN MODIFIED ELECTRODE

This paper describes the electrochemical reduction of nitrite ion in basic media 0.2M KHC03, with glassy carbon or ITO electrodes modified with a conducting polymer derived from Co(II)tetra-3-aminophenyl-porphyrin. Cyclic voltammetry results show an enhancement in the current of the corresponding Co(II)/Co(I) redox couple when the solution contains 0.02M nitrite. When spectroelectrochemical experiments were performed in the support electrolyte, the modified electrode does not stabilize Co(I) oxidation state, but when there is nitrite in the solution a band at 549nm appears, indicating the stabilization of Co(I) oxidation state probably due to the formation of an intermediary complex between the Co(I) and nitrite. Controlled potential electrolysis experiments verify the production of ammonia and hydrazine even at very negative potentials, showing the electrocatalytic character and the stability of this modified electrode

New cyclometalated Ir(III) complexes with bulky ligands with potential applications in LEC devices: experimental and theoretical studies of their photophysical properties

In the present work we report the synthesis and the electrochemical, photoluminescence and electroluminescence properties of two new Ir(III) cyclometalated complexes denoted as [Ir(F2ppy)2L1](PF6) and [Ir(F2ppy)2L2](PF6), where F2ppy is 2-(2,4-difluorophenyl)pyridine, L1 is 4,4′-diphenylethyl-2,2′-bipyridine and L2 is 4,4′-bis[2-[4-(1,1-dimethylethoxy)phenyl]ethyl]-2,2′-bipyridine. The photoluminescence spectra in solution for both the complexes are characterized by wavelength emission maxima at around 510 nm and higher quantum yields. In the solid state, the emission spectrum of the complex with L2 is characterized by higher emission intensity than the [Ir(F2ppy)2L1](PF6) complex. This behavior is explained as due to the effect of the more bulky structure of the L2 ligand, which prevents, in a more efficient way compared to the complex with L1, the auto-quenching processes in the solid packing. DFT calculations were performed to understand the photophysical behavior of the complexes, and an excellent agreement between experimental and theoretical data was observed. For the complex with L2, the electronic density of the HOMO is located in the chain and phenyl fragment of this ligand. This behavior is quite different from that expected for a typical Ir(III) cyclometalated complex, where the electron density of the HOMO is located on the metal (t2g orbitals)/phenyl fragment of the cyclometalating ligand. In spite of these differences, both complexes are good emitters, and in both cases the emission comes from a single T1 emitter state with the contribution of the MLCT and LLCT. In order to get a first approximation of the behavior of these complexes in LEC (light emitting electrochemical cells) applications, the electroluminescence spectra with an applied bias of 12 V were obtained. Both the complexes show yellow-green emissions at around 550 nm, with (0.41, 0.48) and (0.45, 0.48) CIE coordinates for [Ir(F2ppy2)2L1](PF6) and [Ir(F2ppy2)2L2](PF6), respectively.

Electrocatalytic Transformation of Carbon Dioxide into Low Carbon Compounds on Conducting Polymers Derived from Multimetallic Porphyrins

The electrochemical reduction of carbon dioxide is studied herein by using conducting polymers based on metallotetraruthenated porphyrins (MTRPs). The polymers on glassy carbon electrodes were obtained by electropolymerization processes of the monomeric MTRP. The linear sweep voltammetry technique resulted in polymeric films that showed electrocatalytic activity toward carbon dioxide reduction with an onset potential of -0.70 V. The reduction products obtained were hydrogen, formic acid, formaldehyde, and methanol, with a tendency for a high production of methanol with a maximum value of turnover frequency equal to 15.07 when using a zinc(II) polymeric surface. Studies of the morphology (AFM) and electrochemical impedance spectroscopy results provide an adequate background to explain that the electrochemical reduction is governed by the roughness of the polymer, for which the possible mechanism involves a series of one-electron reduction reactions.

SPECTROELECTROCHEMICAL STUDIES ON ITO MODIFIED ELECTRODES WITH A CONDUCTING COBALT (II) MACROCYCLE FILM IN THE ELECTROCHEMICAL REDUCTION OF CO2

The spectroelectrochemical properties of a conducting polymer derived from Co(II) tetra-3-amino-phenyl-porphyrin,(poly-Co(II)-TAPP) were studied towards the electrochemical reduction of CO2 on ITO surface. Under inert atmosphere, the results show that the polymer present a stable Co(I) oxidation state only in basic pH while in more acidic solution this Co(I) does not stabilize. Under CO2 atmosphere the reduced polymer forms a stable adduct with no clear electronic localization. The formation and the stability of this adduct could explain the wide distribution of reaction products

Substituent influence in phenanthroline-derived ancillary ligands on the excited state nature of novel cationic Ir(III) complexes

In the quest for coordination compounds with potential applications in energy conversion processes, a new series of four Ir(III) complexes (C1–4) of the type [Ir(R-ppy)2(Ln)](PF6), where R-ppy = 2-phenylpyridine (ppy) or 2,4-difluorophenylpyridine (F2-ppy) and Ln = 1-methyl-1H-pyrazole[3′,4′:5,6]pyrazino[2,3-f][1,10]phenanthroline (L1) or thieno[3′,4′:5,6]pyrazino[2,3-f][1,10]phenanthroline (L2) has been synthesized. The photophysical properties of these compounds have been thoroughly characterized by both steady-state and time-resolved spectroscopic techniques, pointing out a complex interplay between excited states of different nature that plays a crucial role in the deactivation processes. In the case of complexes C1–2 that feature the same L1 ancillary ligand, the lowest excited states at room temperature are characterized by an admixture between the 3MLCT/3LLCT and 3LC states, with an almost pure 3LC character in C2. For C3–4, the admixture among charge-transfer and ligand-centred states is negligible, due to the appreciably low energy of the LC one, which, however, plays a non-innocent role in the deactivation pathway of the triplet charge-transfer emissive states of complexes C3–4. This work thus highlights the importance of a detailed comprehension of the photophysical properties of Ir(III) complexes in view of their use in energy transformation systems.

ANOMALOUS BEHAVIOR OF Ir(III) CYCLOMETALATED COMPLEXES: APPLICATION IN LIGHT-EMITTING ELECTROCHEMICAL CELLS

The cationic Ir(III) complex with 7,8-benzoquinoline (bzq) as cyclometalating ligand and 4,4´-diterbutyl-2,2´-bipyridine (tBuB) as ancillary ligand, [Ir(bzq) 2 (tBuB)](PF 6 ) (1), was utilized in the fabrication of a light-emitting electrochemical cell (LEC). The photophysical properties and the characterization of the LEC device with this complex was compared with literature data for the analogous complex with 2-phenylpyridine (ppy), [Ir(ppy) 2 (tBuB)](PF 6 ) (2). Complex 1 showed blue shifted emission compared to complex 2. Surprisingly, complex 1 shows lower luminance, efficiency and stability in regard to 2. This behavior correlated well with the low values of quantum yield and lifetime, registered for complex 1 in solution. The performance observed is unexpected, taking into account the emission wavelengths recorded for each complex, and the lesser non radiative deactivation processes expected for a complex with a more rigid ligand as bzq. A possible explanation of this behavior is given in terms of the predominance of a fluorescent emission in the case of the complex 1 instead of a phosphorescent emission, as observed for complex 2.

Heteroleptic Cu(I) complexes bearing methoxycarbonyl-imidoylindazole and POP ligands – an experimental and theoretical study of their photophysical properties

Four new mixed ligand Cu(I) complexes bearing methoxycarbonyl imidoyl-indazole and bis[2-(diphenylphosphino)-phenyl]ether (POP) ligands were synthesized and characterized by variable-temperature NMR, FT-IR, EA and HRMS. For three of them, the molecular structures were obtained by X-ray diffraction analysis. The electrochemical and absorption–emission properties of all the complexes were investigated by using cyclic voltammetry, UV-Vis spectroscopy, and spectrofluorometric measurements in a CH2Cl2 solution at room temperature and in different solid-state matrices. In addition, quantum chemical computations were performed to gain insight into their electronic and photophysical properties. The complexes showed an MLCT band, which is more influenced by the position of the electron-withdrawing methoxycarbonyl substituent in the indazole ring rather than by the π-extension introduced by the alkene moiety. Besides, all the complexes were found to be weak emitters in the CH2Cl2 solution while they were brighter emitters in the solid-state.