Room Temperature Perylene Based Columnar Liquid Crystals as Solid-State Fluorescent Emitters in Solution-Processable Organic Light-Emitting Diodes

The finding of pure organic emitter materials is the need of hour for mass production of cost-effective and metal-free fluorescent organic light-emitting diodes (FOLEDs). In this paper, we report a new series of perylene tetraesters (PTE) that exhibit room temperature columnar (Col) mesophase and can act as efficient fluorescent emitter materials in OLEDs. The molecular design involves the attachment of triazole moieties with PTE discotic core via click chemistry. Triazole groups were chosen as it can improve the electron transport as well as tune the luminescent behavior of the discogens. All the PTE derivatives 3a-d exhibited ordered columnar rectangular (Colro) mesophases at ambient temperature suitable for various device applications. The electron mobility of perylene tetraesters derivative 3a was measured by time of flight (TOF) and exhibits electron mobility of 0.014 cm2/V.s. While the balanced hole and electron charge transport behaviour was observed in fabricated hole-only and electron-only devices. Taking advantages of both charge transport and luminescent nature of the PTE derivative in OLEDs, a series of devices were fabricated by utilizing 3a as a sole emitter and in dispersed form at 1, 5 and 8 wt % with CBP host and 5 wt % in SimCP2 host. A significantly high value of external quantum efficiency (EQE) of 6.5% is obtained in doped device with CBP host at 5 wt % dopant (3a) concentration with CIE coordinates of (0.37, 0.53) correspond to green color. The obtained high EQE value will certainly offer an important step forward to expand the application of smart DLC materials in OLEDs.