Synthesis And Optoelectronic Properties Of Small Molecule Organic Semiconductor Materials Based On Carbazole, Biphenyl And Anthracene

Organic semiconductors have recently received considerable attention because of theirpotential applications such as organic light-emitting diodes (OLEDs), organic field-effecttransistors(OFETs),andphotovoltaiccells.SmallmoleculematerialisanotdesirablepartoftheOrganicsemiconductormaterials. The synthesis and application of carbazole, biphenyl andanthracenederivatives with well knowncharge transporting, highthermal andblueluminescentpropertieshasbeenofgreatinterestforchemistsandmaterialscientists.In this thesis we synthesized several series of small molecule semiconductor materials basedoncarbazole,biphenylandanthracenebyC-CandC-Ncouplingreactions(Ullmann,Buchwaldand Suzuki coupling reaction). Two2,7-carbazole based low molecular weight derivatives,9-hexyl-N2,N2,N7,N7-tetraphenyl-carbazole-2,7-diamine (TPCA) and9’-hexyl-9’H-9,2’:7’,9’’-tercarbazole (HTC), were synthesized by Buchwald and Ullmann coupling reactions,respectively. The optical, electrochemical and thermal properties of this two analogous smallmoleculehostshavebeencharacterized.TheHOMOlevelofTPCAandHTCwere-5.25eVand-5.29eV indicating good hole-transporting properties. Both of the compounds emit deep bluelight peaked at410nm and428nm in solid state. According to the measurement, the LQY ofTPCA is0.98, almost1.7times higher than that of HTC (0.59) in dilute THF solution. Thegeometrical and electronic properties of the compounds were studied using density functionaltheory(DFT) calculations. The studies mentioned above indicate that both TPCAand HTC aresuitableforactivematerialsofbluelight-emittingdiodes.Diphenylamine and thiophene compounds are promising materials for organic light-emittingdiodes (OLEDs). We report here, the synthesis and optical property of a novel small molecularweight derivative, N4.N4,N4’.N4’-tetrakis (4-(thiophen-2-yl) phenyl)-[1,1’-biphenyl]-4,4’-diamine(TPPA). The target molecule was synthesized using4,4’-dibromobiphenyl as the startingmaterial, and the proceeding reactions included bromination, Buchwald and Suzuki couplingreactions.Accordingtotheopticalcharacterizationofit,theabsorptionpeak andexcitationpeakis at351nm and412nm, respectively. The luminescence quantum yields (LQY) of TPPA ismeasuredat61.3%.The new semiconductor that was composed of a anthracene core unit and diphenylamine on both sides, N2,N2,N6,N6-tetraphenylanthracene-2,6-diamine (TPAA), was synthesized byBuchwald coupling reaction. The obtained compound was characterized by UV-visiblespectroscopy, fluorescence spectrum, cyclic voltammetry, and thermal gravimetric analysis(TGA). The novel synthesized derivative showed high thermal stability, with a field-effectmobilityof2.9×10-3cm2/Vsandanon/offcurrentratioof8.0×103.