In this study Ruthenium (II) tris (2, 2’-bipyridyl) complex in nonaqueous solution was studied by cyclic voltammetry and also its kinetic parameters were calculated. The redox reaction of ruthenium (II) trisbipyridyl complex is totally quasi-reversible and it can be described as a diffusion-controlled process. As a result of the redox reaction, the kinetic parameters of the electrode process such as diffusion coefficient (D), and heterogeneous rate constant (ks) were calculated. In addition, the different thermodynamic parameters such as standard free energy (ΔG#), enthalpy change (∆H#), and entropy change (∆S#) were determined and enthalpy change revealed the exothermic behavior of the electrode reaction. Both oxidation and reduction onset potentials of the ruthenium (II) trisbipyridyl complex was determined under the same experimental conditions to estimate the low ionization potential and electron affinity. The electrochemical and optical band gaps of the ruthenium (II) complex were compared.

Spectroelectrochemical study on a new absorption band of radical cations of 4,4’-bis[N-(1-naphthyl)-N-phenyl-amino]-biphenyl (α-NPD) as an electron-donor hole-transporting material used in organic electronics is reported in this work. UV-visible spectroscopic and cyclic voltammetric properties for α-NPD in solution are also examined. We find that the results are attributed to quenching process for blue fluorescence from α-NPD by excess α-NPD+ radical cations accumulated in the emission region in the organic light-emitting devices related to a relatively large overlap between the fluorescence spectrum of α-NPD and the absorption spectrum of α-NPD+ radical cations. The band gap energy for α-NPD is calculated from the UV-visible spectroscopic data.

In this study, we report the luminescence quenching by radical cations of aromatic diamines used as a hole transport layer (HTL) in organic electroluminescent (EL) devices. The EL characteristics of green organic EL devices with an electron transport layer (ETL) as an emitter i.e. ITO/TPD HTL/Alq3 ETL/Al is studied. Here, ITO, TPD, and Alq3 are abbreviations for indium-tin-oxide, N,N’-diphenyl-N,N’-bis(3-methylphenyl)-1,1’-biphenyl-4,4’-diamine, and tris (8-hydroxyquinoline) aluminum, respectively. UV-visible absorption and electrochemical data indicate the formation of radical cations in thin film and solution of TPD after chemical oxidation. We find that the EL luminance increases less than linearly with an increase in current for the EL devices studied in this study. The luminance loss in the devices is attributed to quenching of singlet excited states by large excess radical cations of TPD are accumulated in the emission zone due to large overlap between a flourescence spectrum of Alq3 and an absorption spectrum of radical cations of TPD.