Synthesis And Characteristic Study Of Perylenediimide-cored Dendrimer With Fluorinated Shell

As a novel displaying technique with promising application in flat-panel displays,organic light-emitting diodes (OLEDs) have received more and more attention by virtue of the following properties: direct current driving, self-luminous, small volume, fast response, full color emission,wide view angle and simple manufacture techniques.Currently the red light-emitting materials and devices still lag behind the green and blue components in both efficiency and stability and require further improvements to match the criteria of full-color displays and white-light lighting. Nowadays to develop red host emitters for non-doped light-emitting diodes has become a prevalent strategy to gain highly efficient red electroluminescence (EL). The functional dendrimers are just enough to supply the demand.Dendrimers are branched macromolecules that consist of a core, one or more dendrons, and surface groups.They possess considerable advantages over the well-developed conjugated polymers and small molecular light-emitting materials , whose luminescence can be finely tuned by changing the core with a wide range of luminescent chromophores. Furthermore , various functional surface groups and different generations can be selected to generate the interesting properties such as carrier-transporting , site isolation , solubility and antenna effects. A perylenediimide-based dendrimer PDI-F was designed and synthesized for application as red host emitter in non-doped organic light-emitting diodes. PDI-F was synthesized via Diels-Alder cycloaddition. Its structure was confirmed by ~1HNMR,MALDI-TOF- MS and XRD . The thermal and morphological stability of PDI-F were investigated by means of differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Its photo-electricities are determined by UV-vis Spectra, Photoluminescent Spectra, Cyclic Voltammetry. And PDI-F was used as electron transporting and emitting layer to fabricate non-doped OLED by spin coating method.PDI-F exhibits good solubility in common organic solvents and is suitable for wet methods such as spin coating to make thin films. Perylenediimide was selected as the luminescent core due to its red fluorescence and high fluorescent quantum yield. Pentafluorophenyl rings were grafted to the dendrimer surface with the aim to function as electron transporting moieties. The dendrimer constructed in this way is bulky and non-planar as verified by single crystal structure. Furthermore, it has a remarkably high glass transition temperature of 235℃and a decomposition temperature of 425℃, indicating the excellent morphological and thermal stability.The photoluminescence (PL) spectrum of PDI-F film is nearly identical to that of dilute solution, excluding intermolecular stacking and emission quenching. PDI-F-based single-active-layer non-doped light-emitting device exhibited red electroluminescence with maximum at 602 nm. The EL spectra are driving voltage independent and identical to the PL spectra, suggesting the stable emission properties of PDI-F. Its band gap (Eg), electron affinity (Ea) and ionization potential (I_P) were calculated as 2.06 eV, 3.6 eV and -5.66 eV, respectively, indicating an efficient electron injection from cathode to dendrimer layer if it is used as electron injecting and transporting layer in OLEDs.