The literature has shown numerous contributions on the synthesis and physicochemical properties of persistent organic radicals but there are a lesser number of reports about their use as building blocks for obtaining molecular magnetic materials exhibiting an additional and useful physical property or function. These materials show promise for applications in spintronics as well as bistable memory devices and sensing materials. This critical review provides an up-to-date survey to this new generation of multifunctional magnetic materials. For this, a detailed revision of the most common families of persistent organic radicals—nitroxide, triphenylmethyl, verdazyl, phenalenyl, and dithiadiazolyl—so far reported will be presented, classified into three different sections: materials with magnetic, conducting and optical properties. An additional section reporting switchable materials based on these radicals is presented (257 references).

Playing with organic radicals as building blocks for functional molecular materials

Activation of aromatic CH bonds by a transition metal catalyst has received significant attention in the synthetic chemistry community. In recent years, rapid and site-selective extension of π-electron systems by C-H activation has emerged as an ideal methodology for preparing organic materials with extended π-systems. This Review focuses on recently reported π-extending C-H activation reactions directed toward new optoelectronic conjugated materials.

Synthesis of extended π-systems through C-H activation.

Mixed-valence (MV) compounds are excellent model systems for the investigation of basic electron-transfer (ET) or charge-transfer (CT) phenomena. These issues are important in complex biophysical processes such as photosynthesis as well as in artificial electronic devices that are based on organic conjugated materials. Organic MV compounds are effective hole-transporting materials in organic light emitting diodes (OLEDs), solar cells, and photochromic windows. However, the importance of organic mixed-valence chemistry should not be seen in terms of the direct applicability of these species but the wealth of knowledge about ET phenomena that has been gained through their study. The great variety of organic redox centers and spacer moieties that may be combined in MV systems as well as the ongoing refinement of ET theories and methods of investigation prompted enormous interest in organic MV compounds in the last decades and show the huge potential of this class of compounds. The goal of this Review is to give an overview of the last decade in organic mixed valence chemistry and to elucidate its impact on modern functional materials chemistry.

Organic mixed-valence compounds: a playground for electrons and holes.

Many kinds of radicals are stable enough to isolate, handle, and store without any special precautions. The diversity in molecular architectures of these stable radicals is sufficiently large that the common factors governing radical stability/persistence, geometric and electronic structure, association/dimerization preferences, and reactivity have generally not been well articulated or appreciated. This review provides a survey of the major classes of stable or persistent organic/organomain group radicals with a view to presenting a unified description of the interdependencies between radical molecular structure and properties.

What's new in stable radical chemistry?

Persistent carbon-centered radicals

Inert carbon free radicals. I. Perchlorodiphenylmethyl and perchlorotriphenylmethyl radical series

: The preparation of perchlorotoluene and perchloro-p-xylene was effected starting from 2,3,4,5-tetrachloro-1-trichloromethylbenzene and 1,4-bistrichloromethylbenzene, respectively, by means of a powerful nuclear chlorinating agent. 1,3,5-Tristrichloromethylbenzene was inert under the same conditions. Chlorination of 2,4,6-trichloromesitylene with chlorine and white light gave 2,4,6-trichloro-1,3,5-trisdichloromethylbenzene and products of chlorinolysis, no perchloromesitylene being isolated. Perchlorotoluene and perchloro-p-xylene readily underwent chlorinolysis under photochlorination conditions. 2,3,5,6-Tetrachloro-1-trichloromethylbenzene, 2,5-dichloro-1,4-bistrichloromethylbenzene and 2,3,5,6-tetrachlorobenzoic acid, are also reported for first time. Some significant results related with the preparation and stability of these chlorocarbons are explained on the basis of steric strain and distortion. (Author)

Preparation of highly strained aromatic chlorocarbons. i. a powerful nuclear chlorinating agent. relevant reactivity phenomena traceable to molecular strain.

The syntheses of 1,1',3,3',6,6',8,8'-octachloro-9,9'-bifluorenylidene (1), its precursors, and the byproduct 3,3',5,5'-tetrachloro-4-(trichloromethyl)biphenyl (5) are described. Accurate structural X-ray data on 1 and on perchloro-9,9'-bifluorenylidene (2) are reported and discussed. Because of chlorine overcrowding, the dihedral angles between their two identical fluorenylidene moieties are abnormally large, the central-ethylene twist angles being 55 and 66 degrees, respectively. Significant out-of-plane carbon-chlorine bond bending is likewise exhibited. Their ESR spectra and magnetic measurements prove that they are singlet species. The exceptionally large bathochromic displacements of their UV-vis absorption spectrum with respect to that of their parent hydrocarbon are mainly attributed to bond bending and molecular warping.

1,1',3,3',6,6',8,8'-Octachloro-9,9'-bifluorenylidene and perchloro-9,9'-bifluorenylidene, two exceedingly twisted ethylenes.

Inert carbon free radicals. 2. Monofunctionalized tetradecachlorotriphenylmethyl radicals and related compounds

Synthese par condensation selon Friedel Crafts de polychloro benzenes avec le chloroforme en presence de AlCl 3

Manuel Ballester

Papers

Inert carbon free radicals. I. Perchlorodiphenylmethyl and perchlorotriphenylmethyl radical series

Preparation of highly strained aromatic chlorocarbons. i. a powerful nuclear chlorinating agent. relevant reactivity phenomena traceable to molecular strain.

1,1',3,3',6,6',8,8'-Octachloro-9,9'-bifluorenylidene and perchloro-9,9'-bifluorenylidene, two exceedingly twisted ethylenes.

Inert carbon free radicals. 2. Monofunctionalized tetradecachlorotriphenylmethyl radicals and related compounds

An easy, high-yield synthesis of highly chlorinated mono-, di- and triarylmethanes