| Abstract [eng] |
Anthracenes are well known organic semiconductor compounds with unique configuration of singlet and triplet excited states. Anthracenes demonstrate triplet – triplet annihilation (TTA) process which enables a substantial boost in the quantum efficiency of OLED devices. However, a close molecular packing is crucial to achieve an efficient TTA process. In this work we analyze the energetic properties of anthracenes in a physical and covalent dimer configuration. The efficient TTA process in physical form of 9,10 – aryl substituted anthracene derivatives was achieved. The intensity of delayed fluorescence was related with the rate of intersystem crossing, which was enhanced in more conjugated compounds. Thin-film preparation conditions were also shown to affect TTA properties in differently disordered amorphous state and a lower energetic disorder can drastically affect TTA efficiency. Thus, a low energetic disorder in solid state is required. Lower energetic disorder can be created with chemically conjugated anthracene monomers, known as 9,9’ – bianthryl derivatives. However, strong excitonic interaction between anthracene monomers induces charge transfer states in higher polarity environments, which deteriorates overall emission efficiency. With aromatic substitutions in 9,9‘ – bianthryl core at 2,2‘ – positions, the efficient suppression of internal charge transfer process (ICT) was achieved. The expressed emission of locally excited states enabled up to 3 times enhanced emission efficiency in various environments. To achieve low disorder in amorphous phase, the geometry of anthracene dimers can be flattened by conjugated the structure into so called V – shaped anthracene dimers, serving as heptacene analogs. The control of the strength of dimer interaction in V – shaped heptacenes enabled a wide – range tuning of emission efficiency, radiative and non – radiative decay rates and HOMO – LUMO energy level distribution, while a substantial enhancement of photostability was also achieved. These properties can be beneficial for future organic optoelectronic devices. |
