(714e) Synthesis and Properties of Novel Luminescent Compounds Containing Triphenylamine and Thiophene Units

Organic light emitting
devices(OLEDs) based on low molecular weight organic
materials have attracted much attention because of their potential application
in full-color and flat-panel displays. In these devices, N,N,N',N'-tetraphenylbenzidine
(TPD) derivatives are
often used as hole-transporting materials (HTMs) due to their strong electron
donating ability, high charge mobility and good thermal stability. But because
of the poor solubility, these HTMs can not be used to fabricate OLEDs by solution
forming film methods with commercial significance (such as spin-coating and
ink-jet printing) to form large-area solid films. Hence, it is necessary to
prepare high solubility materials. The TPD-based HTMs can be easily synthesized
in moderate yields using cheap raw materials by well-known organic reactions including
the Vilsmeier and Wittig reactions. In this paper, we
designed and synthesized two compounds H1 and H2 (Fig.1) containing TPD
donors, thiophene
acceptors and olefinic linkers. The structures were characterized
via MS, ¹H NMR, FT-IR. H1 and H2 exhibit
excellent solubility in common solvents and good film forming properties. The
UV-Vis absorption and fluorescence emission spectra of the two compounds in
dilute chloroform and on the solid films were measured. It reveals that compounds H1 and H2 exhibit
similar spectral behavior. The two compounds exhibit two absorption peaks in
the regions of 311-313nm and 353-380nm. For the emission spectra in chloroform
solution, the maximum emission peaks are 520nm and 501nm for H1, H2
respectively, corresponding to green light emission. The thermal properties of
the two compounds were investigated by differential scanning calorimetry (DSC). The two compounds show similar glass
transition temperature (T_g) of 104.04°æ and 103.60°æ. Cyclic voltammetry measurements show that these compounds have
proper HOMO levels for hole injection. In order to
investigate the electron distribution of the HOMO and LUMO energy levels of
these two compounds, quantum chemical calculations were carried out through the
Gaussian 03 program at the B3LYP/6-31G* level. The results show that compounds
H1 and H2 have linear structures and proper highest occupied molecular orbital(HOMO) levels. The properties of compounds H1 and H2
indicate that these two compounds are candidates for the application in
OLEDs as HTMs.

Fig. 1
Molecular structures of compounds H1 and H2