Well-ordered films of disk-shaped thermally activated delayed fluorescence molecules

We fabricated well-ordered, crystalline mono- and multilayers of disk-shaped thermally activated delayed fluorescence (TADF) molecules such as 4CzIPN, 2CzPN, and 5CzBN. The slow deposition of these molecules on flat substrates such as Ag(111) at room temperature resulted in the formation of well-ordered and homogeneous monolayers. Moreover, the multilayer of the 4CzIPN was also found to be well-ordered and flat when deposited on highly oriented pyrolytic graphite (HOPG). The electronic states of the crystalline monolayer and multilayer of 4CzIPN were found to be nearly the same, suggesting that the electronic states of both layers are not altered significantly by adsorption on substrates. Indeed, we also confirmed the delayed fluorescence from the crystalline multilayer of 4CzIPN on the HOPG substrate even in an ambient condition. These results show promising applications of crystalline films of disk-shaped TADF-molecules such as 4CzIPN for organic light-emitting diodes devices with high outcoupling efficiency.