Current Organic Synthesis - Volume 9, Issue 2, 2012

π-Conjugated organic small molecules and polymers have found a number of applications for use in plastic electronics. One key aspect of organic materials is their versatility. Organics exhibit a remarkable flexibility in the synthesis at molecular level, allowing for tunability of a wide range of properties. Additionally, their use offers the prospect of low manufacturing costs, large area coverage, lightweight and compatibility with flexible substrates. This special issue of Current Organic Synthesis is dedicated to this exciting research area, focusing on the latest developments in the design and synthesis of functional π-electron systems, their bulk and surface/interface self-assembly, their structureproperty- performance relationships, and device applications. To highlight the breadth in scope of this area, contributions from world-class leading scientists whose research addresses organic materials but from quite different perspectives and in varying context are gathered together. The Authors provide an up-to-date discussion on main and emerging applications, spanning photovoltaics (OPVs, DSSSCs), light emitting devices (OLEDs), electrochemically-gated transistors, sensors, and nanoelectronic devices. Fluorinated poly(p-phenylenevinylene)s and their oligomeric counterparts represent an attractive class of materials for electroluminescent device applications, which is extensively reviewed in the article by G. Farinola et al. The review focuses on the synthetic methodologies, and also discusses structure-(electro)optical properties relationships as a function of the number and positions of the fluorine atoms on the conjugated backbone. S. Achelle et al. summarize recent advances in molecular design and synthesis of pyrimidine π-conjugated architectures, and their applications as organic field-effect transistors, liquid crystals, sensors, and non-linear optical (NLO) materials. Mechanically interlocked molecules such as catenanes and rotaxanes are finding interesting applications in the field of artificial molecular machines and electronic devices, due to the availability of new and efficient template-directed synthetic protocols. Both kind of materials have been reviewed in detail in the articles by D. Lanari, L. Vaccaro et al. and by G. Fioravanti, respectively. A comprehensive overview on the computational investigation of representative examples of metal-free organic dyes employed as photosensitizers in dye-sensitized solar cells (DSSC), is given in the article by M. Pastore, F. De Angelis et al. This review also focuses on the matching between theoretical calculations and experimental measurements.

This review reports a survey of our recent results on the synthesis of arylenevinylene polymers and oligomers selectively functionalized with fluorine atoms on aromatic and/or vinylene units. The synthetic methods developed are based on Pd-catalyzed organometallic cross-coupling reactions and in particular on the Stille coupling between vinyl organotin derivatives and aromatic halides. Several compounds have been synthesized, which differ for the number and position of the fluorine atoms on the conjugated backbone, even combined with other functional groups. The effects of fluorination on optical properties both in solution and solid state are discussed.

In the past two decades, π-conjugated organic compounds have attracted much attention due to their potential applications in various fields such as liquid crystals, light-emitting, and nonlinear optical materials and self assembling. Introduction of heteroaryl moieties into π-extended systems are particularly useful where electron transfer is necessary and is a way to modify and sometimes enhance properties of advanced “electro-optic”. In π-conjugated materials, azaheterocycles such as pyrimidine, which owing to its aromaticity, its strong electron-withdrawing character, its high dipolar interaction and its pH sensibility, presents the requested characteristics to be incorporated in organic materials in view of numerous and various applications. Such molecular architectures and their applications are reported in this review.

Mechanically-interlocked molecules have been considered for many years only aesthetically appealing structures but nowadays they are finding interesting applications in the field of artificial molecular machines and electronic devices. Improved template-directed protocols have allowed highly programmable and efficient syntheses of rotaxanes and catenanes. In particular those compounds which exhibit bi- and multistability are reliable candidates for the construction of molecular switches. Recently, great efforts have been directed towards the incorporation of these molecules into integrated nanosystems. The first step of this challenge consists in transferring such mechanically-interlocked molecules from solution to surfaces without altering their switching properties. An overview of [2]catenanes that have been synthesized and deposited into surfaces with the aid of various techniques is presented, furthermore some attempts of incorporating such compounds into molecular devices are discussed.

Rotaxanes are currently seen as one of the most promising components in artificial molecular machines. In the last few decades, much effort has been dedicated to the developing of such interlocked architectures, which can be subjected to different types of submolecular motion. The field of Rotaxanes has evolved to stimuli-responsive molecular shuttle, capable of responding to several different external stimuli. The interest in molecular shuttles arises from the possibility of achieving controlled submolecular motion of their components with respect to one another. Here, we present an overview of benzylic amide rotaxanes, smart molecules able to function as electrochemically switchable molecular shuttles, both in solution and on surfaces. Transposing working systems from the solution phase onto surfaces and into the solid state is fundamental for their applicability in different technological fields including electromechanical switches and molecular electronic devices. The synthesis of benzylic amide rotaxanes is based on template effects mediated by hydrogen bonds, which play a key role also in the shuttling process. Given the electrostatic nature of hydrogen bonds, their interactions can be modulated through injection of electrons. Electrochemistry seems to be a powerful reagent-free tool to operate stimulus and characterize the molecular level motion across different environments, necessary from the point of view of future integration with current technologies.

A comprehensive overview on the main applications of state-of-the-art computational methodologies to the simulation of Dye- Sensitized Solar Cells (DSSCs) based on metal-free organic dyes is reported. The presented results cover two crucial aspects that should be carefully taken into account in the design of novel and highly efficient sensitizers, namely the electronic structure of the dye (spectroscopic and redox properties) and its interactions with the TiO2 surface. Concerning the electronic structure calculations, our results demonstrate that a proper TDDFT formulation can successfully describe the excited state properties of a series of organic dye sensitizers, yielding results of comparable quality to high-level correlated ab initio calculations. Our work on the adsorption and aggregation of organic dyes on TiO2 surfaces show that the adopted integrated computational strategies and models can realistically simulate and predict the interaction of the dyes with the TiO2 substrate, thus underlying the main factors responsible of DSSC efficiency.

Self-assembly provides a unique method for creating supramolecular functional materials. A significant progress in the synthesis and characterization of boronic acid-based supramolecular structures has been achieved in recent years. Macrocycles, dendritic structures, polymers, rotaxanes, and cages have been assembled using four types of reversible reactions. We herein elucidate the key point of the strategy, the parallel utilization of two or more of these reactions, by reviewing remarkable contributions over the last few years. It is hoped the reviewed material will stimulate further investigations that will result in producing new interesting boron-based structures in the near future.

Recent advances in the development of environmentally friendly recyclable reagents and catalytic systems based on hypervalent iodine are discussed. The review covers the following topics of active current research: polymer-supported iodine(III) and iodine(V) oxidants, recyclable monomeric hypervalent iodine(III) reagents, reactions of hypervalent iodine in solid state, application of water or recyclable organic solvents in these reactions, and catalytic systems based on hypervalent iodine compounds. These efficient and ecofriendly reagents and catalytic systems are now widely used in organic synthesis for various oxidative transformations of organic substrates.

The cyclocondensation of anilines with propargyl alcohols in the presence of catalytic amount of CuCl and CuCl2·2H2O to afford 1,2-dihydroquinolines with high atom-efficiency in moderate to good yields is developed.