Fluorine Segregation in Crystalline Materials: Structural Control and Solid-State [2+2] Cycloaddition in CF3-Substituted Tetrathiafulvalene Derivatives
Résumé
The well-known influence of long perfluorinated chains on the structures and stability of amphiphilic molecules in liquid crystalline mesophases or mesoscopic micellar arrangements is evaluated here in the realm of crystalline materials based on rigid aromatic molecules bearing only a limited number of CF3 moieties. Tetrathiafulvalene (TTF) derivatives bearing one or two CF3 groups, that is, (Z)- and (E)-(CF3)2TTF ((Z)-1, (E)-1), EDT-TTF-CF3 (2), and EDT-TTF(CF3)2 (3) (EDT=ethylenedithio) are prepared from the 1,3-dipolar reaction of methyl 4,4,4-trifluorotetrolate with ethylenetrithiocarbonate. The structures of neutral (Z)-1, (E)-1, 2, and 3 as indicated by single-crystal X-ray diffraction measurements reveal the recurrent formation of layered structures with a strong segregation of the fluorinated moieties and formation of fluorous bilayers, attributed to the amphiphilic character of those TTF derivatives upon CF3 functionalization, and without need for longer CnF2n+1 (n>1) perfluorinated chains. The short intermolecular distance between outer CC double bonds observed in the layered structure of (E)-1 allows a solid-state [2+2] photocyclization with formation of chiral dyads incorporating the characteristic cyclobutane ring. These dyads containing two dihydrotetrathiafulvalene moieties facing each other exhibit reversible oxidation to the mixed-valence radical cation state and organize in the solid-state into the same layered structures with fluorous bilayers.