Contrast Enhancement in Polymeric Electrochromic Devices Encompassing Room Temperatu re Ionic Liquids

We report the preparation and spectro - electrochemical characterization of electrochromic devices (ECD) combining inkjet - printed WO 3 as cathode and electro - deposited V 2 O 5 as anode. ECD were prepared for the first time with an optimized formulation of gel polymer electrolyte based on Bisphenol A ethoxylate dimethacrylate and Poly(ethylene glycol) methyl ether methacrylate (BEMA/PEGMA) encompassing the Room Temperature Ionic Liquid (RTIL, 1 - Ethyl - 3 - methylimidazolium bis(trifluoromethylsulfonyl)imide) as solvent. The UV - VIS spectrum of ECD was recorded at different potentials during Li + insertion and de - insertion; additionally the Percent Trasmittance (T%) of ECD vs. time was investigated during repeated bleaching and coloring cycles allowing thus the esti mation of switching times and device stability. Due to the lower ionic conductivity and the apparent superior solvent permeability within WO 3 active layer, RTIL containing ECD showed slower switching times, but higher contrast with respect to the similar o nes with EC/DEC as solvent. These results indicate that the ECD containing environment - friendly RTIL electrolytes are suitable for applications requiring high contrast, high safety and moderately fast switching times

New materials for electrochemiluminescence

The study of electrochemiluminescence (ECL) involves photophysical and electrochemical aspects. Excited states are populated by an electrical stimulus. The most important applications are in the diagnostic field where a number of different biologically-relevant molecules (e.g. proteins and nucleic acids) can be recognized and quantified with a sensitivity and specificity previously not reachable. As a matter of fact the electrochemistry, differently to the classic techniques as fluorescence and chemiluminescence, allows to control the excited state generation spatially and temporally. The two research visits into A. J. Bard electrochemistry laboratories were priceless. Dr. Bard has been one of ECL pioneers, the first to introduce the technique and the one who discovered in 1972 the surprising emission of Ru(bpy)3 2+. I consider necessary to thank by now my supervisors Massimo and Francesco for their help and for giving me the great opportunity to know this unique science man that made me feel enthusiastic. I will never be grateful enough… Considering that the experimental techniques of ECL did not changed significantly in these last years the most convenient research direction has been the developing of materials with new or improved properties. In Chapter I the basics concepts and mechanisms of ECL are introduced so that the successive experiments can be easily understood. In the final paragraph the scopes of the thesis are briefly described. In Chapter II by starting from ECL experimental apparatus of Dr. Bard’s laboratories the design, assembly and preliminary tests of the new Bologna instrument are carefully described. The instrument assembly required to work hard but resulted in the introduction of the new technique in our labs by allowing the continuation of the ECL studies began in Texas. In Chapter III are described the results of electrochemical and ECL studies performed on new synthesized Ru(II) complexes containing tetrazolate based ligands. ECL emission has been investigated in solution and in solid thin films. The effect of the chemical protonation of the tetrazolate ring on ECL emission has been also investigated evidencing the possibility of a catalytic effect (generation of molecular hydrogen) of one of the complexes in organic media. Finally, after a series of preliminary studies on ECL emission in acqueous buffers, the direct interaction with calf thymus DNA of some complexes has been tested by ECL and photoluminescence (PL) titration. In Chapter IV different Ir(III) complexes have been characterized electrochemically and photophysically (ECL and PL). Some complexes were already well-known in literature for their high quantum efficiency whereas the remaining were new synthesized compounds containing tetrazolate based ligands analogous to those investigated in Chapt. III. During the tests on a halogenated complex was unexpectedly evidenced the possibility to follow the kinetics of an electro-induced chemical reaction by using ECL signal. In the last chapter (V) the possibility to use mono-use silicon chips electrodes as ECL analitycal devices is under investigation. The chapter begins by describing the chip structure and materials then a signal reproducibility study and geometry optimization is carried on by using two different complexes. In the following paragraphs is reported in detail the synthesis of an ECL label based on Ru(bpy)3 2+ and the chip functionalization by using a lipoic acid SAM and the same label. After some preliminary characterizations (mass spectroscopy TOF) has been demonstrated that by mean of a simple and fast ECL measurement it’s possible to confirm the presence of the coupling product SAM-label into the chip with a very high sensitivity. No signal was detected from the same system by using photoluminescence

Improvements in the Characterization of the Crystalline Structure of Acid-Terminated Alkanethiol Self-Assembled Monolayers on Au(111)

We report a study of acid-terminated self-assembled monolayers of alkanethiols of different length, 11-mercaptoundecanoic acid (11-MUA) and 16-mercaptohexadecanoic acid (16-MHDA), on Au(111). Scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and contact angle techniques were used for characterization, and the results were compared with those obtained from n-alkanethiols of similar chain length, providing a detailed description of the two-dimensional crystalline structure. Molecular resolution STM images show that 11-MUA forms a dense-packed monolayer arranged in a (root 3 x root 3)R30 degrees structure with a c(2 x 4) superlattice, where the simple hexagonal phase, the c(2 x 4) superlattice, and nonordered areas coexist. 16-MHDA assembles in a uniform monolayer with similar morphology to that of 11-MUA, but molecular resolution could not be reached in STM due to both the hydrophilicity of the acid groups and the poor conductivity of the thick monolayer. Nevertheless, the monolayer thicknesses estimated by XPS and electrochemistry and the highly blocking character of the film observed by electrochemistry as well as the low water contact angle are consistent with 16-MHDA molecules forming a compact monolayer on the Au(111) substrate with fully extended alkyl chains and acid groups pointing away from the surface. The results obtained for 16-MHDA were reproducible under different preparation conditions such as the addition or omission of acetic acid to the ethanolic solution. Contrary to other reports, we demonstrate that ordered acid-terminated self-assembled monolayers are obtained with the same preparation conditions as those of the methyl-terminated ones, without any additional treatment

Neutral and Dianionic Ru(II) Bathophenanthrolinedisulfonate Complexes: A Route To Enhance Electrochemiluminescence Performance in Aqueous Media

We report the strong enhancement of ECL intensity and duration in neutral and dianionic Ru(II) complexes bearing mixed 2,2\u2032-bipyridine (bpy) and bathophenanthrolinedisulfonate (BPS) ligands. In aqueous conditions, using the tripropylamine-assisted method and applying a constant potential, we observed for Ru(BPS)(bpy)2 a remarkable 26-fold ECL integrated intensity increase with respect to Ru(bpy)3 2+. The results herein obtained reveal that the cause of reduced ECL intensity of [Ru(BPS)3]4- and [Ru(BPS)2(bpy)]2- can be ascribed to surface effects related to the interaction of the oxidized complex with the electrode. The expected reduction or absence of electrostatic interactions with biomolecules, together with the strongly enhanced performance, makes the zwitterionic Ru(BPS)(bpy)2 complex a highly promising candidate for the development of very efficient ECL labels for ultrasensitive bioassays and functional imaging applications

Electrochemistry and spectroelectrochemistry of polypyridine ligands: A theoretical approach

The 2,3-bis(2-pyridyl)pyrazine (2,3-dpp) and 2,5-bis(2'-pyridyl)pyrazine (2,5-dpp) have been successfully used as bridging ligands for building up ruthenium (II) and osmium (II) polypyridyl redox and luminescent active dendrimers. Such ligands have been herein investigated by ab initio and DFT theoretical calculations both in gas phase and with the solvent effect. The different molecular conformations exhibited by 2,3-dpp, which depend on whether it is free or coordinated to one or two metal centres, have been explored by performing the scan of the potential energy surface. The spectra of the neutral and the radical anion species of the relevant conformers have been calculated at DFT and semiempirical level of the theory. The results have been assessed by correlating them with electrochemical and UV-Vis-NIR spectroelectrochemical experimental ones, obtained in highly aprotic and dry conditions. (c) 2006 Elsevier B.V. All rights reserved