Gathered Based On The Electron Donor - Electron Acceptor Structure Of The Organic Small Molecule Synthesis, Optical Properties And Molecular Structure

The recent progresses in the fields of both modulating the electronic propertiesand energy transfer/electron transfer in oligomers and polymers with donor-acceptorstructure were summarized in chapter 1. And more, two fundamental research trendswere also outlined. (1) As for the modulating the HOMO/LUMO levels, the oligomerswith donor-acceptor structure emerge as promising candidates. However the relevantreport about the systematic study for the mechanism of modulating HOMO/LUMOlevels is still lacking. No general concept has been established as yet. So one researchstrategy was proposed for this thesis: it emphasized on the synthesis of p-n diblockand triblock oligomers as model molecules, on the systematic investigation of theirelectronic properties, also on the relationship between morphology and the molecularstructure. (2) As for the energy and electron transfer, the existing research workmainly focus on the model molecules. However the report about assembly for them isstill few, through which the multicomponent system can be assembled to nanosacledevices. So another research strategy was accordingly proposed for this thesis: itemphasized on the synthesis of multicomponent system based pyrene-perylenebisimide, on the investigation of the energy and electron transfer process, also on theself-assembly. The abstracts for the other chapters are listed as below.Chapter 2. For the sake of the systematic investigation of the electronic propertiesmodulating principle, a novel series of diblock oligomers (T₂O, T₂O₂, T₄O₂) andtriblock oligomers (OT₂O, T₂O₂T₂), consisting of an electron-rich thiophene unit andan electron-deficient oxadiazole unit with different unit lengths, are successfullysynthesized. We developed a one-pot synthetic route for methyl4-bromo-2,5-bis(octyloxy)benzoate from 1,4-dibromo-bis(octyloxy)-benzene. Andmore, the monobromo-substituted oxadiazole dimer was synthesized successfully forthe first time. The p-n diblock oligomers exhibited excellent band-gap controllingproperties. Changing the thiophene or oxadiazole rings could independently tune theHOMO or LUMO energy level in the p-n diblock oligomers. And more, changingmolecular regiochemistry can also modulate electronic properties of oligomers. Theelectronic properties of diblock oligomers are evidently different from those of itstriblock regioisomer. The study, therefore, provided fundamental insight into theimproved design and understanding of p-n heterostructure oligomer semiconductors. Chapter 3. For the sake of the systematic investigation of the relationship betweenmorphology and the molecular structure, UV-vis spectroscopy, DSC and polarizedoptical microscopy (POM) as well as X-ray diffraction (XRD) were used toinvestigate the crystalline morphology and molecular packing of the oligomers T₂O₂and OT₂O. The observation of morphologies shows the evidence for the differentcrystalline morphologies of the two oligomers. The broad DSC curve indicates asubstantially imperfect crystalline morphology for T₂O₂. Further evidence for this canbe provided by the POM study. The molecules alternate orientation in z-stacks due todonor(thiophene)-acceptor(bisoxadiazole) interaction. However, both less-orderspherular crystal and perfect single crystal-like lamellar laths can be observed for theOT₂O.The single crystal-like lamellar laths are completely translated into spherularcrystal upon heating the sample to 58℃. The molecular structure has evident affect onthe crystalline morphologies. The crystalline morphology for OT₂O with symmetricalmolecular structure has higher perfection than that for T₂O₂ with unsymmetricalmolecular structure. And more, the oligomers can self-assembly and formwell-ordered two-dimensional pattern at solid-liquid interface.Chapter 4. The rod-like pyrene-perylene bisimide molecular triads (Py-Per-Py andPy-e-Per-e-Py) were synthesized. The time-resolved and steady state emission givesclear proof of energy transfer from the pyrene unit (Py*) to the perylene bisimide unit(Per*). And more, the electron transfer from both Py* and Per* to charge separatedstate (CS) can also occur. In polar solvent for both triads, the Py* decays very rapidlyby electron transfer to CS in high yield, and energy transfer to Per* in less yield. Theenergy transfer processes were disturbed by electron transfer in different polarenvironments. Additionally, the energy transfer and electron transfer in the two triadsis different due to the different distance and orientation between donor and acceptor inthem.Chapter 5. For the sake of the investigation of the potential as promising candidatesfor nanoscale devices, the self-assembly behavior at the liquid/solid interface of bothPy-Per-Py and Py-e-Per-e-Py were investigated by Scanning tunneling microscopy(STM). The two triads form well-ordered two-dimensional patterns when physisorbedfrom 1-phenyloctane on graphite (HOPG) at the solid-liquid interface. The moleculeis not standing upright but is lying with its molecular axes parallel to the graphite plane. Along the molecule's long axis, two adjacent molecules'stacking is not withend-to-end model but with staggered model. In the conjunct area, only pyrenemoieties stack. However, along the molecule's short axis, the adjacent moleculesstack with parallel model. The good assembly in company with the uniquephotoelectric properties makes the two triads as promising candidates for nanoscaledevices.