Metal-Free Benzothioxanthene Imide Based Dyes for Organic Light-Emitting Electrochemical Cells

Two synthetic organic dyes of the Benzothioxanthene imide (BTI) family are explored as a promising electroactive material for organic light-emitting electrochemical cells (LECs). The high thermal stability and ease of thin film processing make BTI-based compounds suitable for these devices. However, their planar pi-conjugated structure often leads to aggregation-caused quenching (ACQ), reducing luminescence in the solid state. To overcome this, this study has taken advantage of host-guest interactions with 4,4 '-bis(9H-carbazol-9-yl) biphenyl (p-CBP), poly(9-vinylcarbazole) (PVK), and poly(dioctylfluorene) (PFO) to suppress ACQ. The use of p-CBP improved the internal electrical double layer (EDL) alignment within the film, resulting in higher luminescence compared to PFO and PVK-based LECs. The BTI-F dye, when incorporated into a dual host system with p-CBP and PFO, achieved an impressive luminescence of up to 3900 cd m-2. Additionally, PFO enhanced charge balance, contributing to a blue shift in maximum absorption wavelength and increasing the device's tolerance. A triple-host system (p-CBP, PVK, PFO) further extended the device's half-life (t1/2) to 54 min, demonstrating the potential of these host-guest systems in advancing metal-free LEC technology.