Extended π-Conjugated Quinacridone Based Molecules With Optoelectronic Functions

In recent years, along with the development of organic synthesis as well as the theoryof semiconductor, organic optoelectronic materials have been much improved, andexhibited high potential applications in organic light-emitting diodes （OLEDs）, organicfield-effect transistors （OFETs） and organic solar cells （OSCs）. Compared with traditionalinorganic materials, organic molecules take the advantages of those that the structures andproperties are easy to modify, the purifications are simple, and in particular, the materialscould be fabricated into flexible devices. The performances of the optoelectronic devicesare strongly dependent on the materials ptoperties. Therefore, designs and synthesis of neworganic optoelectronic materials and investigations of the relationships between structuresand properties are quite necessary. Quinacridone （QA） possesses large-conjugatedsystem, high photo and thermal stability, and excellent semiconductor property. Herein, the-conjugated system of QA has been extended, four series of optoelectronic moleculeshave been synthesized, and the relationships between structures and properties have beeninvestigated.1. In chapter II, a series of π-conjugated dendrimers Cn-QA and Tn-QA （n=13）composed of quinacridone core and carbazole dendrons have been designed andsynthesized. These dumbbell-like dendrimers with carbazole dendrons from first to thirdgeneration were obtained by convergent synthetic strategy. Their1H NMR spectra,electrochemical, photophysical properties, and film formation behaviors as well asaggregation structures in solid states have been fully investigated. The relationships between the structures and properties of dendrimers have been established. The electron-withdrawing substituent effects and the limited conjugations of the carbazole dendronshave been studied. Compared with the parent molecule N, N’-di（n-butyl）quinacridone（DBQA）, the HOMO levels of the dendrimers increased and the LUMO levels decreaseddue to the carbazole dendrons substitution. The absorptions and emissions of dendrimersdisplayed red-shift feature compared with that of DBQA, while the higher generationdendrimer displayed slightly blue-shift tendency compared with the lower one. Theaggregation structures of films and solid powder samples could be efficiently modulated bythe carbazole dendrons and tert-butyl groups. In particular, dendrimers C2-QA and C3-QAexhibited piezochromic luminescence phenomenon, and the mechanism was preliminarilyinvestigated.2. In chapter III, two propeller-shaped pentaphenylphenyl （PP） groups have beenconveniently introduced to QA core by three-step classic reactions and the resultedBPP-QA molecule exhibits high emission efficiency in both solution and solid state.Concentration-dependent1H NMR spectra and photophysical measurements reveal thatthe PP groups could efficiently suppress the aggregations of QA cores. Compared withparent molecule C8-QA, the film emission efficiency of BPP-QA is obviously improved.Electrochemical results and DFT calculations indicate that the PP groups haven’tproduced effect on the frontier orbitals of central QA-core. Therefore, BPP-QA stillpossesses the advantage of parent QA molecule. BPP-QA has been employed as dopedemitter to fabricate efficient OLEDs.3. In chapter IV, the structures and properties of indole rings fused quinacridonederivative IDQA have been carefully investigated and compared with its parentquinacridone derivative N, N’-di（n-octyl）quinacridone （C8-QA）. Concentrationdependent1H NMR spectra revealed strong aggregations of IDQA in solutions becauseof the large π-system. Two polymorphs of IDQA with and without π π interactionsexhibited non and red emissions, respectively. The1-dimesional micromaterials ofIDQA fabricated based on reprecipitation approach displayed molecule packing dependent emission properties. The photophysical, thermal and electrochemicalproperties of IDQA were studied. Nine-ring fused planar skeleton endowed IDQA withhigh fluorescence quantum yield （ΦF） of0.91in dilute solution and good thermal andelectrochemical stability. Moreover, the hole mobility of IDQA was as high as0.047cm2V1s1measured by using space-charge limited-current （SCLC） approach.4. In chapter V, a series of regioregular head-to-tail oligo（3-hexylthiophene）-functionalized dicyano-ethylene substituted quinacridine derivatives DCN-Tn-QA （n=1–3） were designed and synthesized. These linear π-conjugated donor–acceptor–donor（D-A-D） molecules with different lengths of the oligothiophene chains have beenachieved in good yields via iterative iodination and Suzuki cross-coupling reactionsfollowed by Knoevenagel condensations. Their photophysical, electrochemicalproperties and density functional theory （DFT） calculations were systematicallyinvestigated. The compounds of DCN-Tn-QA （n=1–3） with intense absorption rangefrom350to750nm, suitable LUMO levels at around–4.0eV and considerable filmformation property, were suitable for the application in organic solar cells （OSCs） asacceptors. The organic bulk heterojunction （BHJ） solar cell based on the blend film ofP3HT: DCN-T2-QA （1:1, w/w） showed a power conversion efficiency （PCE） of0.51%under the illumination of AM.1.5,100mW cm^-2. Compared with P3HT: PCBM, theblend film of P3HT: DCN-T2-QA displayed stronger response to the solar spectrum inlong wavelength range from665to750nm.In summary, we have designed and synthesized four series of conjugated systemsbased on extending QA core. The relationships between structures and properties havebeen carefully investigated. At the same time, some materials with excellentperformences are obtained.