Search

White electroluminescence from a single molecule is a challenging topic in organic light emitting diode (OLED) research. Herein, we report the white light emission from a carbazole derivative, 9-ethyl-3,6-bis(4-(trifluoromethyl)phenyl)-carbazole (Cz(PhCF3)2), by harvesting both singlet and triplet emissions. The blue fluorescence and a broad emission from room temperature phosphorescence resulted in white light electroluminescence (EL) with a colour coordinate of (0.31, 0.44). We successfully synthesized another molecule namely 1,1'-(4,4'-(9-ethyl-9H-carbazole-3,6-diyl)bis(4,1-phenylene))diethanone Cz(PhBz)2 and achieved a four-fold increase in the efficiency of the EL with a substitution change from −Ph-CF3 to −Ph-CO-Ph with a colour coordinate of (0.29.0.35). The present route for the generation of white light emission from a solution processable single organic molecule utilizing both singlet and triplet excitons offers a promising way to improve the efficiency of future white OLEDs.

Development of new efficient luminescent materials is one of the active research areas of interest due to its promising optoelectronic applications including in organic light emitting devices (OLEDs). Among the various luminescent systems, emitters of deep blue electroluminescence with excellent color purity have great deal of importance as these are one of the important components for fabricating white OLEDs. In this context, we have designed and synthesized novel solution processable organic donor-acceptor dyads 1 and 2 having electron donating carbazole and accepting oxadiazole groups. The substitution pattern at the phenylene linker has been changed to understand the intramolecular electron communication between the donor and acceptor moieties of these dyads. The photophysical properties of these dyads were studied in both solution and film state. The emission maxima of the dyads red shifted with the increase in solvent polarity, which could be attributed to the intramolecular charge transfer (ICT) process. In the film state, dyads 1 and 2 showed deep blue emission having λmax at 415 nm and 409 nm, respectively. To understand the structure and band gap of these dyads, density functional theory (DFT) calculations have been performed. In line with the design strategy adopted, high thermal stability and formation of solution processed homogeneous film were obtained. Furthermore, we have fabricated the solution processed un-doped devices based on these dyads 1 and 2, which exhibited deep blue electroluminescence in near ultraviolet (NUV) region having λmax at 410 and 408 nm with a narrow full width at half maximum (FWHM) of 54 and 49 nm and CIE coordinates of (0.16, 0.07) and (0.16, 0.05), respectively, indicating thereby their potential in possible optoelectronic applications.