Self-assembled molecular network with waterwheel-like architecture: experimental and theoretical evaluation toward electron transport capabilities for optoelectronic devices

Abstract

In recent times, self-assembled electron transport materials for optoelectronic devices, both solar cells and organic light-emitting diodes (OLEDs), have been gaining much interest as they help in fabricating high-efficiency devices. However, designing organic small molecular materials with star-shaped self-assembled networks is a challenge. To achieve this sort of target, we chose triazine and benzene-1,3,5-tricarbonyl cores for developing such architecture, and we developed four molecular systems, vizTCpCN, TCmCN, TmCN, and TpCN. Successful isolation of single crystals followed by structural analysis of TmCN revealed interesting molecular arrangements in the solid state resulting in the formation of a waterwheel type architecture with an extended network bearing characteristic voids. Theoretical calculations was carried out to check their electron transportability. The natural transition orbital calculation helped in understanding the locally excited and charge transfer excited states. The low electron reorganization energies of these molecules indicated that these materials may have potential to be used in electron transport layers of optoelectronic devices, particularly in OLEDs. Moreover, the assembled networks have a relatively wide surface area and linked structures, which are advantageous for the conduction of carriers with poor electron recombination inside the ETL, and these may offer a straightforward channel for electron conduction to the emissive layer. Finally, the fabricated electron-only device indicated that the synthesized materials may be used as ETMs in the electron transport layer of optoelectronic devices.