POSSIBLE EVIDENCE FOR QUANTUM-SIZE EFFECTS IN SELF-ASSEMBLED ULTRATHIN FILMS CONTAINING CONJUGATED COPOLYMERS

We present photoluminescence (PL), UV absorption, electroluminescence and x-ray reflectivity studies of self-assembled multilayer films cont aining alternate layers of conjugated copolymers, and nonconjugated in sulating polymers. We show that the PL emission properties of these or ganic quantum wells can be ''tuned'' by a proper choice of the conjuga ted copolymer and the thickness of the insulating layers. Particularly , some of the self-assembled ultrathin films containing thin (similar to 7 Angstrom) insulating polymeric layers exhibit a blue shift upon d ecreasing the thickness of the assembly. The PL shift is roughly propo rtional to 1/d(2) where d is the thickness of the assembly, as expecte d for confined photogenerated electron-hole pair in an infinite square potential well. In contrast, the PL emission of similar assemblies bu t containing thick (similar to 4 Angstrom) insulating layers is indepe ndent of the assembly thickness and exhibit emission in the blue. This may suggest a strong spatial confinement. Light emitting diodes based on self-assembled multilayer films with improved efficiency and stabi lity and with threshold voltage as low as 2.6 V could be fabricated. ( C) 1996 American Institute of Physics.