Synthesis And Optoelectronic Properties Of Organic Electron Transport Ladder Conjugated Materials

Recently, with the steady advances of research work and practical application of organic semiconductors, people are eager for new materials with high mobility and stability and also easy processibility. Ladder conjugated organic semiconductors, with their unique structures connected by two chains, shows good stability and enhanced electron mobility. We chose two kinds of materials, one is ladder conjugated polymer BBL, the other is fused perylene diimides-fluorene with enlarged π conjugated system. In order to solve the problem of poor solubility of ladder conjugated polymer BBL, tetraoctyl naphthalene tetracarboxylic dianhydride (TO-NTCA), a new monomer of BBL, was synthesized and followed by model condensation with ortho-diaminobenzene to give a product tetraoctyl naphthalene benzimidazole (TO-NTCBI). In order to broaden the π conjugate system of perylene diimides, fused perylene diimides-fluorene (compound C) was synthesized. TO-NTCBI and compound C were characterized by NMR and HRMS and their spectral and electrochemical properities were also investigated.1. Tetraoctyl naphthalene tetracarboxylic dianhydride (TO-NTCA), a new monomer for BBL, was synthesized through bromination, esterization, stille coupling, hydrogenization, hydrolyzation with naphthalene tetraboxylic dianhydride as the starting material. Model condensation of TO-NTCA with ortho-diaminobenzene gave tetraoctyl naphthalene benzimidazole (TO-NTCBI), an oligomer of BBL. All unreported intermediates and target molecules were characterized by NMR, HRMS. Solubility measurement showed that TO-NTCBI exhibited a good solubility of20mg/mL in dichlorobenzene at room temperature. Electrochemical measurement showed that the LUMO energy level of Compound was promoted by0.26eV when incorporating four octyl chains to the naphthalene ring. So, four octyl chains caused bad influence to the ability of electron acception. However, TO-NTCBI can still be taken as a potential candidate for organic electron transportation material. Besides, spectral and electrochemical measurement of TO-NTCBI showed a broad absorption and96nm strokes shift, fluorescent quantum yield of0.47. In conclusion, it is an effective method to increase the solubility of polymer by introducing alkyl chains to its monomer while without manifest influence on its optoelectronic property.2. Fused perylene diimides-fluorene (compound C) was synthesized through amidation, bromination, Suzuki coupling, cyclization by incident sunlight with perylene tetracarboxylic dianhydride as the starting material. Perylene diimides was synthesized with amino of long alkyl chain and perylene tetracarboxylic dianhydride which showed good solubility. Compared with perylene diimides, compound C showed broader absorption extended to600 nm. Spectral and electrochemical measurement of compound C with enlarged π conjugated system showed0.14eV decrease of energy gap, which demonstrated effective conjugation of perylene diimides moiety and fluorene moiety. It is worth mentioning that photo-induced cyclization showed a high yield over90%and this synthetic method could also be applied in other systems.