New Concepts in Tetrathiafulvalene Chemistry

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Abstract
Tetrathiafulvalene (TTF) and its derivatives were originally prepared as strong electron‐donor molecules for the development of electrically conducting materials. This Review emphasizes how TTF and its derivatives offer new and in some cases little‐exploited possibilities at the molecular to the supramolecular levels, as well as in macromolecular aspects. TTF is a well‐established molecule whose interest goes beyond the field of materials chemistry to be considered an important building block in supramolecular chemistry, crystal engineering, and in systems able to operate as machines. At the molecular level, TTF is a readily available molecule which displays a strong electron‐donor ability. However, its use as a catalyst for radical–polar crossover reactions, thus mimicking samarium iodide chemistry, has only recently been addressed. Important goals have been achieved in the use of TTF at the macromolecular level where TTF‐containing oligomers, polymers, and dendrimers have allowed the preparation of new materials that integrate the unique properties of TTF with the processability and stability that macromolecules display. The TTF molecule has also been successfully used in the construction of redox‐active supramolecular systems. Thus, chemical sensors and redox‐switchable ligands have been prepared from TTF while molecular shuttles and molecular switches have been prepared from TTF‐containing rotaxanes and catenanes. A large synthetic effort has been devoted to the preparation of the so‐called organic ferromagnets, many of which are derived from TTF. The main task in these systems is the introduction of ferromagnetic coupling between the conduction electrons and localized electrons. TTF has also played a prominent role in molecular electronics where TTF‐containing D‐σ‐A molecules have allowed the preparation of the first confirmed unimolecular rectifier. Recently, it has been confirmed that TTF can display efficient nonlinear optic (NLO) responses in the second and third harmonic generation as well as a good thermal stability. These findings can be combined with the redox ability of TTF as an external stimuli to provide a promising strategy for the molecular engineering of switchable NLO materials. Fullerenes endowed with TTF exhibit outstanding photophysical properties leading to charge‐separated (CS) states that show remarkable lifetimes.