TOPOLOGICAL CHANGE OF 4, 4'-BIS[9-DICARBAZOLYL]-2, 2'-BIPHENYL (CBP) BY INTERMOLECULAR REARRANGEMENT

Recently, 4, 4’ -bis[9-dicarbazolyl]2, 2’ -biphenyl (CBP) has been widely used as a host material in OLEDs [1] ~ [10]. However, there are a few reports on the basic physical and chemical properties of CPB. In this study, we report on photoluminescence (PL) characteristics in various aggregated morphologies such as deposited film and single crystal, and discuss its physical and chemical properties. The structure of a CBP molecule is composed of biphenyl in both ends connected by two carbazoles, as shown in Fig. 1. First, we prepared a CBP thin film with a thickness of 100 nm by high-vacuum thermal evaporation onto a silicon substrate and the single crystal by using gas flow-train sublimation method. We prepared the thin film, solution and single crystal to clarify basic physical and chemical properties of CBP. Photoluminescence spectrum and lifetime in the each condition of CBP were determined by using a streak camera. Figure 2 shows the PL spectra of CBP in solution, amorphous film, aged film, and single crystal, respectively. Here, the aged film corresponds to the partially crystallized film due to storage in ambient air for two months. Both PL spectra in amorphous CBP film and CBP in solution (solvent: dichloromethane [CH2Cl2]) showed broad FWHM. Further, a change of the PL spectrum in the thin film was observed in the aged film.