Luis R. Dinelli

Investigation of Ground- and Excited-State Photophysical Properties of 5,10,15,20-Tetra(4-pyridyl)-21H,23H-porphyrin with Ruthenium Outlying Complexes

The present work employs a set of complementary techniques to investigate the influence of outlying Ru(II) groups on the ground- and excited-state photophysical properties of free-base tetrapyridyl porphyrin (H(2)TPyP). Single pulse and pulse train Z-scan techniques used in association with laser flash photolysis, absorbance and fluorescence spectroscopy, and fluorescence decay measurements, allowed us to conclude that the presence of outlying Ru(II) groups causes significant changes on both electronic structure and vibrational properties of porphyrin. Such modifications take place mainly due to the activation of nonradiative decay channels responsible for the emission quenching, as well as by favoring some vibrational modes in the light absorption process. It is also observed that, differently from what happens when the Ru(II) is placed at the center of the macrocycle, the peripheral groups cause an increase of the intersystem crossing processes, probably due to the structural distortion of the ring that implies a worse spin-orbit coupling, responsible for the intersystem crossing mechanism.

Singlet excited state absorption of porphyrin molecules for pico- and femtosecond optical limiting application

This work employs the Z-scan technique with 120fs pulses to investigate the singlet excited state absorption spectra of tetrapyridyl and tetrasulfonatophenyl porphyrins. We have used a three-energy-level model to adjust Z-scan curves in order to obtain the singlet excited absorption cross section from 460to800nm. Starting from these values, we determine the spectra of the ratio between excited and ground singlet state absorption cross sections, whose values are as good as the best found in the literature for reverse saturable absorbers. The results obtained point these porphyrins as good candidates for applications in optical limiting of ultrashort pulses.

Dynamic saturable optical nonlinearities in free base tetrapyridylporphyrin

Dynamic optical nonlinearities in free base tetrapyridylporphyrin (H2TPyP) solutions were investigated at 532 nm with the Z-scan technique. We observed a reverse saturable absorption process that was found to have a fast contribution related to the singlet population and a slow accumulative contribution arising from the triplet population. The optical excitations and subsequent relaxations can be interpreted with a five-energy-level diagram that allows determination of the excited states photophysical parameters such as triplet and singlet absorption cross-sections and the intersystem crossing time.

Reverse saturable absorption in 5,10,15,20-Tetra(4-pyridyl)-21H,23H-porphyrin with ruthenium outlying complexes

Investigations on the excited state absorption signal of 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphyrin, modified by either changing the central ion or adding peripheral groups, were performed using 5 ns laser pulses at 532 nm, in association with linear absorbance and fluorescence decay time measurements. The reverse saturable absorption (RSA) increases remarkably when Zn2+ replaces H+ at the central position of the porphyrin ring. However, it decreases when RuCl2(CO)(PPh3)2 and RuCl2(CO)(dppb) groups are attached at outlying positions through the pyridine rings, for both the free base and zinc porphyrins. A theoretical model based on Jablonski diagram was used to verify the main reason for the decrease on the RSA signal caused by ruthenium groups.

Electropolymerized supramolecular tetraruthenated porphyrins applied as a voltammetric sensor

Porphyrin 5,10,15,20-Tetra(4-pyridyl)manganese(III), [Mn-TPyP(H2O)2]PF6, and electropolymerized supramolecular porphyrins (ESP), {Mn-TPyP(H2O)2[RuCl3(dppb)]4}PF6 (dppb = 1,4-bis(diphenilphosphine)butane), were synthesized and characterized. A thin solid film of ESP was obtained on a glass carbon electrode surface by a cyclic voltammetry method. The peak current increased with the number of voltammetric cycles, which shows a typical behavior of the species being adsorbed on the surface of the electrode. Cyclic voltammetry was also employed for acetaminophen quantification using an ESP modified electrode. The modified electrode shows a linear relationship between the anodic peak current and the concentration of acetaminophen (in the rage 0.05 to 0.7 mmol L - 1). The performance of the modified electrode was verified by the determination of acetaminophen in a commercial pharmaceutical product and the results were in good agreement with those obtained by a control HPLC method.

A new electrochemical sensor containing a film of chitosan-supported ruthenium: detection and quantification of sildenafil citrate and acetaminophen

This work presents the construction of a novel electrochemical sensor for detection of organic analytes, using a glassy carbon electrode (GCE) modified with a chitosan-supported ruthenium film. The ruthenium-chitosan film was obtained starting from the mer-[RuCl3(dppb)(H2O)] complex as a [1,4-bis(diphenylphosphine)butane] (dppb) precursor, and chitosan (QT). The structure of the chitosan-supported ruthenium film on the surface of the glassy carbon electrode was characterized by UV-Vis spectroscopy, electron paramagnetic resonance (EPR), scanning electron microscopy (SEM), atomic force microscopy (AFM), powder X-ray diffraction (XRD) and atomic absorption spectroscopy (AAS) techniques. The glassy carbon electrode was modified with a film formed from the evaporation of 5 µL of a solution composed of 5 mg chitosan-supported ruthenium (RuQT) in 10 mL of 0.1 mol L-1 acetic acid. The modified electrode was tested as a sensor for sildenafil citrate (Viagra® 50 mg) and acetaminophen (Tylenol®) detection. The technique utilized for these analyses was differential pulse voltammetry (DPV) in 0.1 mol L-1 H2SO4 (pH 1.0) and 0.1 mol L-1 CH3COOK (pH 6.5) as supporting electrolyte. All analyses were carried out during a month using the same electrode. The electrode was washed only with water in between the analyses, keeping it in the refrigerator when it was not in use. This electrode was stable during the period utilized showing no degradation and presenting a linear response over the evaluated concentration interval (1.25 × 10-5 to 4.99 × 10-4 mol L-1).

Influence of gold nanoparticles applied to catalytic hydrogenation of acetophenone with cationic complexes containing ruthenium

Herein the catalytic activity of cationic ruthenium(II) complexes [Ru]+ is described in the presence of gold nanoparticles (AuNPsn−) in the transfer hydrogenation of acetophenone, to produce phenylethanol. The catalytic activity of the complexes, with a general formula cis-[RuCl(CH3OH)(P–P)(N–N)]+ or cis-[RuCl(CH3OH)(P)2(N–N)]+ {where: P = triphenylphosphine (PPh3); P–P = 1,1-bis(diphenylphosphino)methane (dppm); 1,2-bis(diphenylphosphino)ethane (dppe); 1,3-bis(diphenylphosphino)propane (dppp), 1,4-bis(diphenylphosphino)butane (dppb); N–N = 2,2′-bipyridine; 4,4′-dimethyl-2,2′-bipyridine} was investigated in the presence of AuNPsn−. The interaction between [Ru]+ and AuNPsn− citrate capped is an electrostatic interaction, by a self-assembly processes, to produce a supramolecular species, labeled as [Ru]+/AuNPsn−. This non-covalent interaction has no effect over the chemical and physical chemical parameters of the complexes, which provides a good point of comparison in the presence and absence of AuNPsn−. The AuNPsn− alone have no catalytic activity in the transfer hydrogenation of acetophenone within 24 h of reaction. However, the AuNPsn− have improved the catalytic activity of the complexes that have biphosphines with tensioned or large bite angle, while for the complexes that have biphosphines with a strong chelate effect a decrease in the catalytic activity was observed. The evidence is supported by experimental values of the yields of the hydrogenated product and DFT calculations of the “RuP–P” intermediates. Suitable crystals of cis-[RuCl2(dppe)(bipy)], cis-[RuCl2(dppp)(bipy)] and cis-[RuCl(CH3OH)(dppb)(bipy)](PF6) were obtained and the X-ray structures are presented here.

An electronic device based on gold nanoparticles and tetraruthenated porphyrin as an electrochemical sensor for catechol

The aim of this study was to obtain an electrochemical device between the electrostatic interaction of the electropolymerized porphyrin {CoTPyP[RuCl3(dppb)]4}, where TPyP = 5,10,15, 20-tetrapyridilphorphyrin and dppb = 1,4-bis(diphenylphosphino)butane, and gold nanoparticles (AuNPsn−), to be used as a voltammetric sensor to determine catechol (CC). The modified electrode, labelled as [(CoTPRu4)n8+-BE]/AuNPsn− {where BE = bare electrode = glassy carbon electrode (GCE) or indium tin oxide (ITO)}, was made layer-by-layer. Initially, a cationic polymeric film was generated by electropolymerization of the {CoTPyP[RuCl3(dppb)]4} onto the surface of the bare electrode to produce an intermediary electrode [(CoTPRu4)n8+-BE]. Making the final electronic device also involves coating the electrode [(CoTPRu4)n8+-BE] using a colloidal suspension of AuNPsn− by electrostatic interaction between the species. Therefore, a bilayer labelled as [(CoTPRu4)n8+-BE]/AuNPsn− was produced and used as an electrochemical sensor for CC determination. The electrochemical behaviour of CC was investigated using cyclic voltammetry at [(CoTPRu4)n8+-GCE]/AuNPsn− electrode. Compared to the GCE, the [(CoTPRu4)n8+-GCE]/AuNPsn− showed higher electrocatalytic activity towards the oxidation of CC. Under the optimized conditions, the calibration curves for CC were 21–1357 µmol l−1 with a high sensitivity of 108 µA µmol l−1 cm−2. The detection limit was 1.4 µmol l−1.