| In this paper, we have designed and synthesized a series of fullerene dyads whichconsists of a rigid [60]fullerene, a phenyl segment substituted with multi-alkoxy chains asthe soft part, and a multi-methylene unit as a flexible space connecting the two segments,utilizing the supramolecular liquid crystals formation method and the decoupling methodof liquid crystal polymers. The influences of the non-convalent bonds, length of theflexible space and terminal alkoxy chains, structure and number of terminal alkoxy chains,on the liquid crystalline phase were studied by means of different characterizationmethods, including differential scanning calorimetry (DSC), polarized optical microscopy(POM), small-angle X-ray scattering (SAXS), one dimensional and two dimensional wide-angle X-ray diffraction (1D WAXD,2D WAXD), transmission electron microscope(TEM), electron diffraction (ED) and atomic force microscope (AFM). We found thatthese dyads self-organize to form two dimensional crystals by π-π interactions betweenfullerenes and microphase separation between the rigid and soft parts, and thesupramolecular fullerene liquid crystals with hierarchical structures were formed by thefree stacking of two dimensional(2D) crystals. These dyads form a novel kind ofthermotropic [60]fullerene supramolecular liquid crystals, which are formed by freestaking of2D crystals. Compared to normal liquid crystals, these supramolecular liquidcrystals have the advantage of high C60content and low transition temperature from crystalstate to liquid crytal state. The design strategy can be applied to design new types ofsupramolecular liquid crystals with hierarchical structures formed by the self-organziationof2D crystals. The detailed content including:1. Synthesis and characterization of T-Cn-Cm-C60(n=9-12,14,16) possesses a gallicester segment substituted with three long terminal alkyl chains (n=9-12,14,16). ForT-Cn-C8-C60(n=9-12,14,16), they all have liquid crystalline phase, and thesemoleculers undergo self-organization driven by π-π interactions between fullerenes andmicrophase sepration to form triper-layer2D fullerene crystals sandwiched within the molten alkyl chain layers, while the free lamellar packing of2D crystals gives rise tothe formation of supramolecular liquid crystals (LCs). For each dyad, the lamellardistance (d) decreased as the temperature increased, indicating the formation of SmCphase. As the length of the terminal alkyl chains increased, the transition temperatureof liquid crystalline state to isotropic state (Ti) decreased, while the transitiontemperature of crystal state to liquid crystal state (Tm) increased. For the compoundwith very short flexible spacer (T-C14-C4-C60), it cannot form2D crystals, and does nothave any liquid crystal phase. This indicates that the formation of2D crystals is criticalto the formation of LC phase.2. Synthesis and characterization of T-Cn-C8-C60(n=4-8) possesses a gallic estersegment substituted with three short terminal alkyl chains (n=4-8). These dyadspossess two liquid crystalline phases. For those with n=4-7, two SmA phases formedwith different lamellar distance and order: the SmA1phase formed in lower temperaturerange and SmA2phase formed in higher temperature range, respectively. The lamellardistance of SmA1of T-C4-C8-C60and T-C7-C8-C60is much larger than SmA2, with longrange order. The lamellar distance of SmA1in T-C5-C8-C60and T-C6-C8-C60is about1nm smaller than SmA2. For T-C8-C8-C60, it forms SmC phase at lower temperaturerange, and SmA phase at higher temperature range, which behaves as a transition statebetween T-Cn-C8-C60(n=4-7) and T-Cn-C8-C60(n=9-12,14,16). For the whole seriesT-Cn-C8-C60(n=4-12,14,16), the lamellar distance of SmA2increased as the terminalalkyl chain lengths increased roughly. For SmC phase, the lamellar distance of T-Cn-C8-C60(n=8-12) increased with the odd-even effect.3. Synthesis and characterization of m-B-Cn-C8-C60(n=8,10,12,14) possessing abenzoic ester segment substituted with two terminal alkyl chains (n=8,10,12,14).These dyads have the similar phase behavior of LCs as T-Cn-C8-C60: the smecticsupramolecular liquid crystalline phase is formed by the free stacking of2D crystals.However, the supramolecular LCs formed by these dyads have a lower Ti, and asmaller range of LC temperature campared to T-Cn-C8-C60(n=8,10,12,14). Thephase behavior changes with the length of the alkyl chains. m-B-C8-C8-C60and m-B-C10-C8-C60form SmC, while m-B-C12-C8-C60and m-B-C14-C8-C60form SmA.4. Synthesis and characterization of OEG-Cm-C60(m=8,10,12) possessing a gallic estersegment substituted with three triglycol as terminal chains, a multi-methylene unit connecting the terminal chains and C60. Thay have the similar liquid crystal phasebehavior as T-Cn-C8-C60. In these fullerene dyads, OEG-C8-C60possesses SmA phase,while OEG-C10-C60and OEG-C12-C60have two SmA phases. For OEG-C10-C60andOEG-C12-C60, the lamellar distance of SmA1phase is larger than SmA2phase. Ingeneral, the lamellar distance increased as the length of the flexible space increased. |
