Abstract

It has recently been shown that ordered, organic thin films of planar stacking molecules can be grown with monolayer uniformity and control over large substrate distances by the ultrahigh vacuum process of organic molecular beam deposition (OMBD). Due to this ability to grow films with such a high degree of order, it was demonstrated by So, et al^1,2 that multiple quantum well stacks consisting of alternating layers of the archetype compounds, ^3,4,9,10 perylenetetracarboxylic dianhydridc (PTCDA) and 3,4,7,8 naphthalenetetracarboxylic dianhydride (NTCDA) exhibit exciton quantum confinement That is, energy shifts in the absorption spectrum, as well as time resolved photolumincscence indicates systematic changes with layer thickness, as the thickness is reduced from 500Å to 10Å. While these early data were compelling, they opened up many questions as to the nature of excitons in closely packed organic molecular systems. Hence, in this work, we have extended this early investigation by measuring the electroabsorption, the absorption and the fluorescence spectra of organic MQW stacks consisting of PTCDA+NTCDA, as well as 3,4,9,10 peryleneietracarboxylic-bis-benzimidazole (PTCBI)+NTCDA. These new investigations provide further information essential to understanding the nature of excitons in these van der Waals-bonded molecular solids.

© 1995 Optical Society of America