AIE-Active Fluorene Derivatives for Solution-Processable\nNondoped Blue Organic Light-Emitting Devices (OLEDs)

Abstract

A series\nof fluorene derivatives end-capped with diphenylamino\nand oxadiazolyl were synthesized, and their photophysical and electrochemical\nproperties are reported. Aggregation-induced emission (AIE) effects\nwere observed for the materials, and bipolar characteristics of the\nmolecules are favored with measurement of carrier mobility and calculation\nof molecular orbitals using density functional theory (DFT). Using\nthe fluorene derivatives as emitting-layer, nondoped organic light-emitting\ndevices (OLEDs) have been fabricated by spin-coating in the configuration\nITO/PEDOT:PSS­(35 nm)/PVK­(15 nm)/<b>PhN-OF­(</b><i><b>n</b></i><b>)-Oxa</b>(80 nm)/SPPO13­(30 nm)/Ca­(8 nm)/Al­(100\nnm) (<i>n</i> = 2–4). The best device with <b>PhN-OF­(</b><b>2</b><b>)-Oxa</b> exhibits a maximum\nluminance of 14 747 cd/m², a maximum current efficiency\nof 4.61 cd/A, and an external quantum efficiency (EQE) of 3.09% in\nthe blue region. Investigation of the correlation between structures\nand properties indicates that there is no intramolecular charge transfer\n(ICT) increase in these molecules with the increase of conjugation\nlength. The device using material of the shortest conjugation length\nas emitting-layer gives the best electroluminescent (EL) performances\nin this series of oligofluorenes.