Charge-transporting organic semiconductors are an important class of materials that play crucial roles in electronic and optoelectronic devices such as organic light-emitting devices (OLEDs), thin film transistors, and photovoltaic cells.
1-7OLEDs, that have organic hole-and electron-transport layers sandwiched between two electrodes, show low driving voltage and bright emission and are of importance for application to full color flat-panel displays and lighting.8-14 Since electron mobilities in organic materials, in general, are several orders of magnitude lower than hole mobilities, electron-transport materials (ETMs) with high electron mobility are required to further improve OLED performance. To achieve an effective electron injection and transport in an OLED, a high electron affinity to enable efficient electroninjection and a high electron mobility to enhance electron flux, with a high ionization potential. Also, electron transporting materials should have a high triplet energy to confine excitons within the emissive layer. It is also reported that electron transporting organic semiconducting materials develop of fulfilling several requirements, many research groups reported that low molar mass compound or polymeric structure containing π electron deficient heterocyclic moieties such as pyridine, oxadiazole, triazole, triazine, quinoline, or quinoxaline.
15-24Recently, we have developed 2,5-bis-(4-triphenylsilanylphenyl)-[1,3,4]oxadiazole (BTSO), that functions as good hole blocker and electron transporting layer in the phosphorescent devices.
25In this study, we designed bis(4-(2,3-di(pyridin-2-yl)pyrido[2,3-b]pyrazin-7-yl)phenyl)diphenyl-silane (DPPDS) with pyridyl-pyridopyrazine, which is composed of tetraphenyl silicone core and high electron attractive π conjugated pyridyl-pyridopyrazine side chains. Silyl groups are well known for their oxidative, thermal and chemical stabilities, low dielectric constants, and good film-forming ability. Moreover, these moieties render a molecule sterical hinderance (bulkyness) in terms of the sp 3 -hybridized silicon atoms. The tetraphenyl silicone core can give effectively hinder the aggregation and excimer formation. The introduction of pyridines on the 2,3-position of pyridopyrazine can not only enhance electron affinity but also reduce intermolecular interaction of fused pyridopyrazine.
Experimental DetailsMeasurement. The 1 H NMR spectra were recorded using a Bruker Advance 300 spectrometer. The thermal analysis was performed on a TA TGA 2100 thermogravimetric analyzer in a nitrogen on a TA instrument 2100 DSC. The sample was heated at 20. Differential scanning calorimeter was conducted under nitrogen on a TA instrument 2100 DSC. The sample was heated at 20UV-vis absorption studies were carried out using Perkin-Elmer LAMBDA-900 UV/VIS/IR spectrophotometer. The photoluminescence (PL) spectra were measured on a Perkin-Elmer LS-50 fluorometer utilizing a lock-in amplifier system with a chopping frequency of 150 Hz. Cyclic voltammetry (CV) was performed on an EG and...