OPV系列分子之自組裝光電超分子奈米結構： 合成,製作,結構,及性質探討

Abstract

In this work, we have synthesized two self-assembling molecules, PEO17-OPV3 and OHC-Tri-BHPV-CHO, to study the relationships between fabrication, structures, and properties of their associated self-assembled supramolecular nanostructures. In Chapter 2, amphiphilic molecule PEO17-OPV3 was synthesized and its aggregation behaviors in the solutions were investigated. By surface tension measurement, the critical aggregation concentration (CAC) was determined as 3.67 x 10-4 M. Since the existence of conjugated segments in PEO17-OPV3, it was also a light-emitting compound. The luminescence properties were highly affected by concentration variations either in polar solvent as water or in apolar solvent as toluene. The CAC calculated by photoluminescence was 5 x 10-4 M which was very consistent with that obtained from surface tension measurement. It indicated that the molecular packing and supramolecular architectures associated with the conjugated compounds could be investigated by photoluminescence technique. The ring-like architecture directed by PEO17-OPV3 was observed on mica surface. The diameter was 30 nm with a peripheral region of about 5 nm. The dimension of enclosed section was the same as the length of amphiphilic molecules. Thus, π-π interaction was reasonably supposed as the driving force to direct this structure. Besides, the twisted center of sulfonate group also played an important role for forming structure. PEO17-OPV3 hybrid systems were reported and discussed. Ring-like thin disks of 150 nm in diameter were observed in PEO17-OPV3 / silica system. Interestingly, the thickness was about 0.65 nm which was very similar to the width of OPV3 segment. That indicated the basic packing unit was the same as their neat PEO17-OPV3 through π – π stacking. Thus, multi-lamellar model was proposed to explain the formation mechanism. While PEO17-OPV3 served as a structure-directing agent for co-organizing with titania precursors, nano hollow-rods and their aggregating microspheres could be fabricated as shown in Chapter 3. The formed microspheres of ~1 μm observed by SEM were composed of bundles of hollow-rods. By grinding the microspheres, isolated hollow-rods of ~100 nm in diameter were collected and investigated by TEM and AFM. Two sets of crystalline plane, rutile (110) and (101), in the skin of hollow-rods were resolved. While the OPV3 packing domains of the hollow-rods were stained with RuO4, the rutile layer of the skin was rip off and the stained inner layer of ~20 nm in diameter could be clearly observed by TEM. A cylinder with a core-shell skin model was proposed to explain the formation of nano hollow-rods. In Chapter 4, side-chain containing PPV trimer (OHC-Tri-BHPV-CHO) was synthesized, and the molecular packing in apolar solvent as well as in polar solvent was investigated. As OHC-Tri-BHPV-CHO was dissolved in hexane, its photoluminescent (PL) spectra in solution shifting with concentration provided information for the transformation from the molecular emission to aggregated emission. The transition concentration was estimated as 3 x 10-5 M. Its self-organized crystalline tubular supramolecular architectures were revealed by atomic force microscopy (AFM) as well as by transmission electron microscopy (TEM). Moreover, from the lattice image and FFT pattern of these organic nanotubes taken by cryo-TEM, we were able to visualize the molecular stacking of OHC-Tri-BHPV-CHO resulted from the π-π interaction. In addition, current-sensitive AFM was employed to measure the conductivity of as-formed nanotubes. The conductivity of this well-ordered oligo-PPV material was up to ~ 10-1 S/cm, much higher than that of the undoped PPV film and comparable to the doped one. Similar results were taken in decane case despite of the lower conductivity of ~ 10-3 S/cm. It was proposed that OHC-Tri-BHPV-CHO molecules initially packed into sheet-like textures in apolar solvents (hexane and decane) by π-π interaction and dipole-dipole interaction between aldehyde groups if hydrogen bonding was not ready to form. Because the sheets were too thin, they would roll up into tubes in order to minimize the surface energy. We also applied a polar solvent (chloroform) as a medium. Nano-strips, rods and rings were observed. In polar solvent as chloroform, OHC-Tri-BHPV-CHO molecules tended to pack into a thin strip by means of π-π interactions and dipole-dipole interaction between aldehyde groups. The aliphatic side chains should be forced to tilt by chloroform so that the ether groups could be exposed for dipole attraction. In the concentrated solution, the thin strips tended to stack into multilayer strips, rods and rings through the attractions between exposed ether groups due to the fact that their thickness was multiple of monolayer strips (0.8 nm) as revealed by the height scan of AFM. Besides, because of the rapid drying of the TEM samples, the thin nano-strips tended to stick together along the strip axis to form the wreaths or fused rings. Their conductivity measured by current-sensitive AFM was up to 10-3 S/cm. In Chapter 5, OHC-Tri-BHPV-CHO was hybrid with silica and titania. In titania case, tubular architectures with 100-200 nm in diameter were fabricated as observed by TEM. On the other hand, self-assembled strips of c.a. 35 nm in thickness could be formed in silica case as revealed by TEM and AFM. The fluorescence behavior was also clearly shown by confocal microscope. It indicated that our OHC-Tri-BHPV-CHO molecule could serve a structure-directing agent and give out ordered organic/inorganic nanocomposite materials.