The Application Of Cyclic Voltammetry In Electrosynthesis And Analysis Of Organic Luminescent Materials

Generally electrosynthesized polymers exhibit electrical conductivity and charge transport, while there is very little attention to optimize the optical proper-ties of emitting layer for organic light-emitting diodes (OLEDs). This is due to a variety of factors, including structural defects and doped counterions presenting in the electropolymerization film, which strongly quench the fluorescence. Up to now, the polycarbazoles prepared by electrosynthesis are mainly applied in OLEDs as the layers for hole injection and/or transport, but have not been applied in OLEDs as the light emitting layer. The electropolymerization film is a low-cost technique for patterned LED, so it's very significant if the electropolymerization film can be used as new technique of preparing patterned light emitting layer.In the Chapter 2, the electropolymerization behaviors of an electroactive and luminescent compound TCPC as precursor are studied. The large difference in oxidation potential between polyfluorene and the carbazole units ensures the elec-tropolymerization of the pendant carbazole groups without affecting the polymer backbone. The resultant electrochemical deposition (ED) films are characterized by cyclic voltammetry (CV), UV-vis, fluorescence spectra, scanning electron mic-troscopy (SEM) and atomic force microscopy (AFM). Under the CV mode with potential range of–0.5 V~ 0.85 V vs. Ag/Ag+, the coupling reactions between the carbazole units of TCPC are very efficient while the fluorescent trifluorene seg-ment in TCPC is chemically inert in this potential range, which results in a highly fluorescent film formation on indium tin oxide (ITO) electrode. The deposition parameters for preparing the TCPC-based ED films are optimized, and the best ED film gives the fluorescence efficiency of 45.5% with surface roughness of 2.8 nm and morphologic stability as heating up to 180oC. The light-emitting devices (LEDs) using this ED film as light emitting layer with structure ITO/ ED film (~100 nm)/Ba/Al achieve maximum luminescence and external quantum effi-ciency of 4224 cd/m2 @17 V and 0.72% @11.5 V respectively, which are better than the device using TCPC spin-coating films as emitting layer.In the Chapter 3, we studied the effect of supporting electrolytes (TBABF4, TBAPF6 and TBAAsF6) on electrosynthesized luminescent films. The results showed that the electropolymerization rate is the highest when TBAAsF6 was used as supporting electrolyte. The maximum fluorenscence quantum efficiency of these films is up to 65%. The AFM images show the electrosynthesized polym-erization film prepared by TBAAsF6 as supporting electrolyte had more iform morphology in the same electropolymerization conditions. In the meanwhile, this film showed the best performance for OLEDs than the other two supporting elec-trolytes.In the Chapter 4, we studied a simple electropolymerization deposition tech-nique to prepare luminescent and patterned films for LEDs. The luminescent films are deposited directly on the patterned ITO (Indium Tin Oxide) electrodes through an oxidation coupling reaction of an electroactive and luminescent precursor. The films deposited on the ITO strips (width of 200μm) exhibit smooth surface mor-phology (roughness of morphology surface is about 3.1 nm), well roughness in electrode edge of 1~2μm, and high fluorescence quantum efficiency (>60%). The technique provides a facile route towards a patternable luminescent film and de-vice, because such luminescent ED films can be manipulatively deposited on the electrified electrode.In the Chapter 5, to study the electrochemical properties, the energy level and the band gap of a series of phosphorescent Re (I) complexes, (L)Re(CO)3Cl (L=α,α-diamine), the Cyclic Voltammetry (CV) are applied together with the UV-Vis absorption spectra, photoluminescence spectra and the Self-Consistent B3LYP quanta chemical calculation method. Based on the results, the energy level of (L)Re(CO)3Cl are gotten and the influencing rule of ligands are also draw. (L)Re(CO)3Cl complexes have a single oxidation peak and many reduction peaks. These peaks reflect the HOMO and LUMO energy level of (L)Re(CO)3Cl com-plexes, which were made up of Re-Cl hybrid orbital andπ* orbital of diamine ligands, respectively. Compared with the results from spectra, the band gap results of (L)Re(CO)3Cl complexes calculated from CV is mainly corresponding to the triplet energy level.