Fullerene‐Filled Stilbene Stars: The Balance between Isolated C₆₀ Helices and 3D Networks in Liquid‐Crystal Self‐Assemblies

Abstract

As eries of shape-persistent star-shapedo ligo(phenylene vinylene) liquid crystalsa nd derivatives with fullerene tethered through spacers of differentl engths to one arm were successfully synthesized.S olution studiesb yN MR, UV/ Vis and fluorescence spectroscopy revealed the preferential locationo ft he C 60 acceptori nt he vicinity of the peripheral donor unit, which affects the quenching of the emission of the conjugated stilbenoid scaffold in the donor-acceptor dyad. The fluorescencew as completely absenti nt he liquid crystal phase due to the extraordinary hierarchical self-assembly.I nt his family of mesogens, the intrinsic free space has to be filled either by an extremely tightp ackingo ft he stars or by the fullerenes as guests. Thes pacer lengths control the nanosegregation of the C 60 units in the cavities of the stars in either independent triplehelices or unprecedented 3D networks, in which fullerenes are positioned at the interfaceo fneighboringc olumns. Eventually,the clearing temperatureo fs uch large complex donor-acceptor systems can be tuned by an entropye ffect defined by the length of the spacer. Thea ccessibility of the isotropic phase without decomposition is an importantp rerequisite forf uture alignment studies associated with potentialm ateriala pplications in organic electronics.

Free Space in Liquid Crystals—Molecular Design, Generation, and Usage

“…Although in solution these mesogens show residual fluorescence from the stilbenoid arms, the emission is quantitatively quenched in the solid state, in which three fullerenes are permanently in the vicinity of all donor chromophores (arms), pointing to efficient energy or electron transfer. A comprehensive study of the thermotropic properties of 20a – c as a function of spacer length recently revealed further important aspects: (i) with the length of the spacers an entropy factor contributes to an enormous decrease in the clearing temperature, and (ii) the longer spacer adds the possibility of further intercolumnar nanosegregation of the fullerenes . The latter leads to 3D interwoven networks of fullerenes in addition to the nanosegregated oligo­(phenylenevinylenes) and aliphatic chains, which is the consequence of the competition of space-filling and nanosegregation.…”

The Role of the 1,2,3-Triazolyl Heterocycle in the Helical Columnar Assembly and Electric Field Response

“…From the H-bonding-directed helical columnar examples based on amide and perylene bisimide derivatives, − it was assumed that the helical order was formed with the aid of the triazolyl H-bonding along the columnar axis. Nevertheless, these individual findings cannot provide confirmative evidence for the decisive contribution from the triazolyl H-bonding interactions when considering the helical columnar assemblies of nonheterocyclic LC examples driven by exquisite engineering of the intracolumnar space filling. − Besides helical formation, we wondered why no columnar LCs based on other polar heterocycles have been found to be responsive to an E-field to date.…”

Visualizing the helical stacking of octahedral metallomesogens with a chiral core

“…The importance of efficient molecular packing has already been recognized for the cases of so-called star-shaped mesogens with three arms. [35][36][37] Because star-shaped molecules have ''free space'' between the arms, their assembly structures are stabilized by filling the space with neighboring molecules or guests. 38 In our case, neighboring columns have similar helical manners to fill the ''free space'' (Movie S1, ESI †).…”