Design Strategy for Enabling Multifunctional Properties of Anthracene-based Emitters

The design of multifunctional materials is a challenging and important objective for a wide array of multidisciplinary applications. However, a multifunctional organic emitter exhibiting simultaneous aggregation-induced emission (AIE), multi-responsive polymorphs, mechanoluminescence and electroluminescence have been scarce. In this study, two anthracene based compounds, namely 10-(4-(9H-carbazol-9-yl)phenyl)anthracene-9-carbonitrile (CzPACN) and 10-(4-(di-p-tolylamino)phenyl)anthracene-9-carbonitrile (DTPACN) was designed and synthesized with rigid and flexible donors, respectively. The CzPACN shows the bright blue emission and DTPACN shows the bright green emission in solution. We have demonstrated an effective strategy to achieve three polymorphic phases such as DTPACN-α, DTPACN-β and DTPACN-γ from DTPACN by controlling the temperature. Under mechanical stimuli, highly restricted and non-planar crystals of the structurally tuned polymorphs DTPACN-α, and DTPACN-β exhibited red shifted emission and DTPACN-γ showed blue shifted emission. Conversely, CzPACN is not showing polymorphism and is not sensitive to external stimuli. In addition, blue and green OLEDs were fabricated using CzPACN and DTPACN, respectively, as an emitter and achieved a maximum external quantum efficiency (EQE_max ) of 5.5% and 5.7%, respectively, for blue and green OLEDs. Further, this study suggests designing multi-responsive smart materials via a simple modification by introducing a non-planar unit with a large twist.