ELECTROCHEMISTRY FOR THE DEVELOPMENT OF INNOVATIVE THREE-DIMENSIONAL AND CHIRAL THIOPHENE-BASED ORGANIC SEMICONDUCTORS
Tesi di Dottorato
Data di Pubblicazione:
2013
Citazione:
ELECTROCHEMISTRY FOR THE DEVELOPMENT OF INNOVATIVE THREE-DIMENSIONAL AND CHIRAL THIOPHENE-BASED ORGANIC SEMICONDUCTORS / V. Bonometti ; supervisor: P.R. Mussini ; co-supervisor: F.Sannicolo'; coordinatore: S.Ardizzone. DIPARTIMENTO DI CHIMICA, 2013 Jan 25. 25. ciclo, Anno Accademico 2012. [10.13130/bonometti-valentina_phd2013-01-25].
Abstract:
Organic conducting polymers are efficient materials for a wide range of applications, ranging from energetics and electronics (bulk-heterojunction solar cells, dye-sensitized solar cells, organic light-emitting diodes, organic field effect transistors) to sensoristics, offering the advantage of being light-weight, flexible, low-cost compounds, thus providing a valid and interesting alternative to traditional inorganic semiconductors. Electrochemistry plays an important role in the study of these smart materials, being a powerful tool to determine the mechanisms of the electron-transfer processes occurring during the reduction/oxidation cycles of these molecules when, deposited as films on electrodic surfaces. Cyclic voltammetry is an essential tool for the experimental evaluation of the HOMO and LUMO levels and of the HOMO-LUMO gap, to be compared with spectroscopical and theoretical values, in order to better understand the relationships between structure and electronic properties and to evaluate the most suitable application for the new molecules. In addition, the combination of cyclic voltammetry with electrochemical quartz crystal microbalance EQCM technique and electrochemical impedance spectroscopy (EIS) affords further information about the mechanisms of the electrochemical coupling of polymerogenic units and,the resitance of the polymer films to mass and charge transfers. In the present PhD thesis, innovative thiophene-based organic semiconductors have been designed and characterized by cyclic voltammetry, in combination with many other electrochemical and spectroscopic techniques (EQCM, EIS, in situ UV-Vis-NIR, ESR and circular dichroism spectroscopy, AFM and SEM imaging) in order to obtain a complete insight into the new materials, to better understand their intrinsic properties for a more efficient target-oriented design.
Particular attention was devoted to three-dimensional molecules (i.e., the so called “genetically-modified” spider-like oligothiophenes, derived from a previous work on branched all-thiophene molecules)[1,2] that fulfil the requirements of branching (which provides the polymers with a remarkable solubility in common organic apolar solvents, ensuring an easy processability), of a significative effective conjugation and of the possibility of fine tuning the HOMO and LUMO levels, by suitable structural modifications in the light of possible applications in organic photovoltaics.
Another class of three-dimensional multithiophene compounds is that of the inherently chiral molecules. It would be a highly innovative result to find a material which would combine the potentialities of chirality (i.e., the ordered spontaneous chain assembling induced by chirality, the noncentrosymmetry associated to chiral materials, which is a prerequisite for second order nonlinear optical applications, the ability of chiral molecules to discriminate between antipodes, as required in sensors designed for the detection of chiral analytes, the possibility for a chiral semiconductor to be employed in asymmetric electrosynthesis) with the advantages typical of the conducting polymers (i.e., electrical conductivity, redox and pH switching capability, electrochromism, low cost, easy processability, light weight). According to the literature, the most common strategy to obtain chiral conducting polymers is to attach chiral pendants (i.e. natural sugar and aminoacids, or manmade designed for specific applications) to the conjugated electroactive backbone. The presence of carbon stereocenters invariably characterizes the chiral substituents. Only in few cases, however, significant chirality manifestations have been found in polymers designed according to this strategy, also because the experimental conditions (i.e., solvent, pH,
Tipologia IRIS:
Tesi di dottorato
Keywords:
conducting polymers ; conjugation ; oligothiophenes ; structure–activity
relationships ; chiral semiconductors ; cyclic voltammetry ; spectroelectrochemistry ; inherent chirality
Elenco autori:
V. Bonometti
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