Current Organic Chemistry - Volume 19, Issue 7, 2015

The 1,2,4-triazole system has shown excellent electron-transport and hole-blocking properties owing to its highly electron-deficient nature. Accordingly, a large number of 1,2,4-triazole derivatives have been described as having a wide variety of uses in materials science. Triazoles are widely used in transition-metal complexes or metal-organic frameworks (MOFs), but metal-free 1,2,4-triazole derivatives have also exhibited interesting and useful properties as materials. The use of these derivatives, either as small molecules or polymers, in light-emitting devices has allowed the fabrication of OLEDs, PHOLEDs and PLEDs with excellent properties. Other materials have exhibited liquid crystalline or optical waveguide behavior or have found applications in PEMFCs, organic photovoltaic cells and data storage devices. The aim of this review is to discuss the most important metal-free derivatives bearing 1,2,4- triazole moieties with applications as organic materials.

Traditional Friedel-Crafts acylation reactions of aromatics suffer from low regio-selectivity towards para- or more linear isomers and usually require stoichiometric quantities of Lewis acids, which are hydrolysed to produce toxic waste during aqueous work-up. Zeolites can catalyse and enhance the selectivity in Friedel-Crafts acylation reactions of simple aromatics and heterocycles. For example, high regioselectivity was achieved in acylation of aromatic ethers, aromatic hydrocarbons and heterocycles over zeolites. This brief review highlights the importance of zeolites to enhance the regioselectivity in Friedel-Crafts acylation reactions.

Porphyrins are important macrocyclic compounds that exist in nature, particularly in their metallated forms. Their unique properties have led the chemical community, since the earliest studies, to embrace the challenge of synthesizing porphyrins. In the quest to produce and manipulate the periphery of these macrocyclic systems for more useful and versatile applications, various strategies have been implemented. Among these, the synthesis of macromolecular systems based on covalently linked porphyrins is one of the most interesting. It is generally believed from the large number of studies conducted that inter-porphyrin interactions occur when there is a strong overlap of the macrocyclic π orbitals mediated by the linkage. While nature uses diverse covalent linkages and self-assembled interactions, our mastery of these is still in its infancy. Attempts to imitate and explore nature sometimes provide chemists with a fertile field for synthetic and mechanistic studies. Synthetic bis-porphyrin prepared for a wide variety of purposes have generally utilized covalent linkers to maintain desired geometry and to control the electronic communication between the two porphyrin moieties involved. This review aims to highlight recent synthetic strategies and the various routes employed to design and synthesize these macrocyclic systems as free-base or metallated forms, with linkages of varied nature, to fine tune the overall system properties for particular applications. Because of the extent of this subject in terms of macromolecular porphyrin systems, in this review we have focused only on bis-porphyrin systems, and have ignored coverage of macromolecular and supramolecular porphyrin based systems that involve more than two porphyrin cores.

The photoluminescent (PL) properties of composites based on single-walled carbon nanotubes (SWNTs) and poly(2,2´-bithiophene-co-pyrene) (PBTh-Py), prepared by in situ chemical polymerization of the two monomers in the presence of carbon nanotubes, are reported. We demonstrate that the functionalization of SWNTs with PBTh-Py copolymer is revealed through a gradual quenching process of PL with the increase of SWNT content (semiconducting component) in the composite mass. FTIR spectroscopy indicates the existence of several steric hindrance effects that originate in the covalent functionalization of SWNTs with PBTh-Py copolymer. The film deposition of PBTh-Py copolymer and PBTh-Py/SWNTs composite onto rough Au supports induces changes in the FTIR spectrum, which originate in an adsorption mechanism caused by the preferential orientation of molecules on the metallic support. Surface-enhanced Raman scattering (SERS) spectroscopy reveals the side-wall functionalization of SWNTs with PBTh-Py copolymer by changes in the shapes, peak position and relative intensities of different Raman lines.