Synthesis, optical characterization and computational study of novel organic fluorophores

Over the last three decades lot of interest has been devoted to light harvesting technologies. Recent findings on global warming and energy nonrenewable resources push us to alternative means of storing energy. Sunlight stands indeed as an ideal asset to take advantage of. In this insight Luminescent Solar Concentrators (LSCs) represent a way to decrease the cost of solar photovoltaics. LSC devices usually consist in a thin slab of transparent material (glass or polymer) doped with a fluorescent dye. Upon solar irradiation, a fraction of the emitted light, through means of internal reflection, is collected at the edges of the device where photovoltaic cells are located. Compared to traditional concentrators, which make use of mirrors and lenses, these devices show numerous advantages, such as theoretical higher concentration factors, the ability to work with both diffuse and incident light and no need for tracking devices or cooling apparatuses. Organic fluorescent dyes bearing \u3c0-conjugated electron-donor and -acceptor moieties exhibit intramolecular charge-transfer (ICT) properties, and can therefore show the optical properties required by LSCs such as high quantum yield and high Stokes shift. On account of this, the present dissertation will discuss the synthesis, UV-Vis characterization and computational study of a set of novel unsymmetrical and symmetrical push-pull azole-based dyes. These compounds are characterized by a 1,3-azole 2,5 substituted with two aromatic moieties bearing electron withdrawing (EWG) or electron donating (EDG) groups. Remarkably, the introduction of an heteroaromatic ring usually improves the thermal and chemical stability and the overall polarizability of the fluorophore. The studied compounds were prepared through a robust synthetic pathway involving a palladium and copper-promoted direct C-H arylation reaction as key step. We took into account the effect of the peripheral electron poor funtionality as well as the nature of the central heteroaromatic core. In order to rationalize the experimental results we carried out TD-DFT studies, that allowed us to proper understand the charge tranfer occuring during the electronic transition. After selecting the best fluorophores for our aim, we investigated its efficiency in an LSC prototypes

Transition Metal-Free Direct C-H (Hetero)arylation of Heteroarenes: A Sustainable Methodology to Access (Hetero)aryl-Substituted Heteroarenes

In recent years, environmental and economic reasons have motivated the development of transition metal-free carbon-carbon bond forming reactions and some excellent reviews have covered this research area of particular interest for the pharmaceutical industry. However, none of these reviews has been specifically dedicated to summarize and discuss the results achieved in the rapidly growing field of the transition metal-free direct (hetero)arylation reactions of heteroarenes. This review, which covers the literature from 2008 to 2014, aims to provide a thorough insight into the synthetic and mechanistic aspects of these atom economic and environmentally benign reactions also highlighting their advantages and possible disadvantages compared to conventional methods for the synthesis of arylheteroarenes and biheteroaryls via transition metal-catalyzed reactions

Synthesis and Biological Properties of 2(5H)-Furanones Featuring Bromine Atoms on the Heterocyclic Ring and/or Brominated Substituents

This review deals with the synthesis of unnatural and natural 2(5H)-furanone derivatives featuring bromine atoms on the heterocyclic ring and/or brominated substituents, which have been described in the literature since 1951 up to February 2016. The review has been organized on the basis of six classes of brominated furanone derivatives that were synthesized: i) 2(5H)-furanone derivatives with one bromine atom on the heterocyclic ring; ii) 2(5H)-furanone derivatives with two bromine atoms on the heterocyclic ring; iii) 2(5H)-furanone derivatives featuring one bromine atom on the heterocyclic ring and monobrominated substituents; iv) 2(5H)- furanone derivatives featuring one bromine atom on the heterocyclic ring and dibrominated substituents; v) 2(5H)-furanone derivatives with monobrominated substituents; and vi) 2(5H)-furanones featuring dibrominated substituents. Where possible, experimental details of the syntheses have been reported. Furthermore, the biological properties of the target compounds, including their mutagenic, cytotoxic, enzymatic, anti-inflammatory and photosynthetic inhibitory activities have been summarized, paying particular attention on the compounds that have demonstrated antimicrobial properties via inhibition of quorum sensing and biofilm formation

Tuning of dye optical properties by environmental effects: a QM/MM and experimental study

The present work is aimed to a deeper investigation of two recently synthesized heteroaromatic fluorophores by means of a computational multilayer approach, integrating quantum mechanics (QM) and molecular mechanics (MM). In particular, dispersion of the title dyes in a polymer matrix is studied in connection with potential applications as photoactive species in luminescent solar concentrators (LSCs). Molecular dynamics simulations, based on accurate QM-derived force fields, reveal increased stiffness of these organic dyes when going from CHCl3 solution to polymer matrix. QM/MM computations of UV spectra for snapshots extracted from MD simulations show that this different flexibility permits to explain the different spectral shapes obtained experimentally for the two different environments. Moreover, the general spectroscopic trends are well reproduced by static computations employing a polarizable continuum description of environmental effects

Toward the design of alkynylimidazole fluorophores: computational and experimental characterization of spectroscopic features in solution and in poly(methyl methacrylate)

The possibilities offered by organic fluorophores in the preparation of advanced plastic materials have been increased by designing novel alkynylimidazole dyes, featuring different push and pull groups. This new family of fluorescent dyes was synthesized by means of a one-pot sequential bromination–alkynylation of the heteroaromatic core, and their optical properties were investigated in tetrahydrofuran and in poly(methyl methacrylate). An efficient in silico pre-screening scheme was devised as consisting of a step-by-step procedure employing computational methodologies by simulation of electronic spectra within simple vertical energy and more sophisticated vibronic approaches. Such an approach was also extended to efficiently simulate one-photon absorption and emission spectra of the dyes in the polymer environment for their potential application in luminescent solar concentrators. Besides the specific applications of this novel material, the integration of computational and experimental techniques reported here provides an efficient protocol that can be applied to make a selection among similar dye candidates, which constitute the essential responsive part of those fluorescent plastic materials

Studio sulle possibilita applicative di convenienti catalizzatori supportati commerciali in reazioni di Sonogashira-Hagihara e di Mizoroki-Heck condotte in batch ed in sistemi a flusso.

Obiettivo di questo lavoro di Tesi (come parte di una più ampia serie di studi condotta nel nostro Dipartimento nell’ambito del Progetto FIRB 2010 “Materiali ibridi multifunzionali per lo sviluppo di processi catalitici ecosostenibili”) è lo sviluppo di convenienti reazioni di alchinilazione tipo Sonogashira e di alchenilazioni tipo Heck (due classi di reazioni scelte fra quelle intrinsecamente più pratiche e green, e quindi di maggior interesse applicativo) mediate catalizzatori commerciali supportati. Questi sistemi, anche se evoluti, dovranno essere pratici, economici, facilmente accessibili e accettabili industrialmente, e saranno studiati in reazioni sia in batch che a flusso; particolare cura sarà posta anche nella scelta delle condizioni di reazione da utilizzare, in modo da individuare procedure il più possibile pratiche, economiche ed ecocompatibili. Compatibilmente con la disponibilità delle apparecchiature necessarie, sarà saggiato anche l’effetto del riscaldamento con microonde. Per quanto riguarda le reazioni a flusso il progetto prevede lo sviluppo di reattori pratici e versatili, anche se poco studiati in reazioni di cross-coupling, come quelli basati su sistemi a colonna impaccata (con gli idonei catalizzatori eterogenei scelti), ed il confronto con analoghe reazioni in batch. Il progetto comprende inoltre l’applicazione delle nuove metodologie eventualmente sviluppate, sia in batch che in flusso, in convenienti sintesi di composti di interesse applicativo, naturali e/o farmacologicamente attivi

ChemInform Abstract: Highly Regioselective C-5 Alkynylation of Imidazoles by One-Pot Sequential Bromination and Sonogashira Cross Coupling.

A variety of 2-substituted 5-alkynyl-1H-imidazoles were easily prepared by a one-pot sequential procedure involving a highly regioselective electrophilic C-5 bromination of 1,2-dimethyl-1H-imidazole, 2-chloro-1-methyl-1H-imidazole, and 2-aryl-1-methyl-1H-imidazoles, followed by an efficient palladium/ copper co-catalyzed Sonogashira-type alkynylation

Improved Synthesis of Symmetrical 2,5-Diarylimidazoles by One-Pot Palladium-Catalyzed Direct Arylation Tailored on the Electronic Features of the Aryl Halide

Two methods for the one-pot synthesis of 2,5-diarylimidazoles by palladium-catalyzed direct C-H arylation of 1-substituted imidazoles with aryl bromides have been devised. The first method, promoted by copper(I) iodide, is best suited for electron-poor aryl bromides, and also allows the 2,5-diarylation of thiazole and oxazole. The use of xylene instead of DMA is the key for the efficiency of the second method, which gives the best results with electron-rich aryl bromides

Highly regioselective C-5 alkynylation of imidazoles by one-pot sequential bromination and Sonogashira cross coupling

A variety of 2-substituted 5-alkynyl-1H-imidazoles were easily prepared by a one-pot sequential procedure involving a highly regioselective electrophilic C-5 bromination of 1,2-dimethyl-1H-imidazole, 2-chloro-1-methyl-1H-imidazole, and 2-aryl-1-methyl-1H-imidazoles, followed by an efficient palladium/ copper co-catalyzed Sonogashira-type alkynylation

Achievement of regioselectivity in transition metal-catalyzed direct C–H (hetero)arylation reactions of heteroarenes with one heteroatom through the use of removable protecting/blocking substituents or traceless directing groups

This review with 453 references covers the literature up to the end of April 2015 on the transition metal-catalyzed direct C-H (hetero)arylation reactions of heteroarenes with one heteroatom in which high regioselectivity has been gained by the use of removable protecting/blocking substituents or traceless directing groups. Particular attention has been devoted to illustrate the typical features of these methods, and to summarize the synthetic procedures used for the introduction of removable protecting/blocking groups in the heteroarene substrates and their subsequent removal from the reaction products. The limitations related to the use of protecting/blocking substituents and directing groups, such as an increase in synthetic steps or the fact that, in many cases, the (hetero)arylation reactions assisted by directing groups involve only C-H bonds ortho to the directing group, will also be highlighted