AVS 47th International Symposium
    Organic Films and Devices Thursday Sessions
       Session OF+EL+SS-ThM

Paper OF+EL+SS-ThM2
The Effect of Conjugation Length on the Frontier Orbital Position of Oligothiophene Derivatives at Metal-organic Interface

Thursday, October 5, 2000, 8:40 am, Room 313

Session: Organic Thin Films
Presenter: A.J. Makinen, Naval Research Laboratory
Authors: A.J. Makinen, Naval Research Laboratory
I.G. Hill, Naval Research Laboratory
T. Noda, Osaka University, Japan
Y. Shirota, Osaka University, Japan
Z.H. Kafafi, Naval Research Laboratory
Correspondent: Click to Email
We report an ultraviolet photoelectron spectroscopy (UPS) study of a novel family of end-substituted oligothiophene derivatives with a varying conjugation length, BMA-nT (n=1-4), where n indicates the number of thiophene rings. These new oligothiophene derivatives are thermally and morphologically stable, and unlike unsubstituted oligothiophenes, which undergo luminescence quenching due to the polycrystalline nature of their solid films, the thiophene derivatives form amorphous films. The BMA-nT compounds show luminescence from the blue (n=1) to the orange (n=4), and additionally they posses hole-transport properties making them attractive materials for organic light-emitting diodes (OLEDs). The UPS results show that the position of the highest occupied molecular orbital (HOMO) of the end-substituted oligothiophenes at the metal-organic interface is dependent on the number of thiophene rings present, i.e. the effective conjugation length of the molecule. We will discuss this property and its implications in the context of carrier injection in an OLED.