Trans–cis isomerization assisted synthesis of solution-processable yellow fluorescent maleic anhydrides for white-light generation

• Theoretical design and trans-to-cis isomerization-assisted one-pot synthesis of alkyl-substituted bis(thienyl)maleic anhydrides were performed.
• A new wavelength-upconverting material with favorable absorption and fluorescence properties in the blue and yellow region of the visible spectrum, respectively is discovered.
• A white light-emitting diode (WLED) is fabricated by solution-processing the new material on a blue LED (InGaN, 455 nm) with promising CIE coordinates and color-rendering index (CRI).

Heterocyclic maleic anhydride derivatives have been extensively studied in natural products chemistry over the past few decades. However, their incorporation into optoelectronic devices has lagged behind that of other π-conjugated systems, and they have never been studied in white light emitting diodes (WLEDs). The development of emissive π-conjugated materials for (WLEDs) has been an emerging scientific and technological research area to replace phosphors used in LED-based solid-state lighting. Here, we demonstrate the design, synthesis and characterization of two new highly emissive alkyl-substituted bis(thienyl)maleic anhydrides (C6-Th2MA and C12-Th2MA) with favorable photophysical properties. The new core is synthesized via a novel trans-to-cis isomerization-assisted one-pot reaction, which is demonstrated for the first time in the literature for the synthesis of a bis(heteroaryl)maleic anhydride. Due to its favorable absorption and fluorescence properties in the blue and yellow region of the visible spectrum, respectively, C12-Th2MA is studied as a potential wavelength-upconverting material. A WLED fabricated by drop-casting a polymeric solution of C12-Th2MA on a blue LED (InGaN, 455 nm) yields promising CIE coordinates and color-rendering index (CRI) values of (0.24, 0.20) and 65.0, respectively. Considering the simplicity of the current molecular structure and facile synthesis, alkyl-substituted bis(thienyl)maleic anhydrides stand as ideal phosphor alternatives. Therefore, the current findings may open new perspectives for the development of maleic anhydride-based small molecules for low-cost, energy-efficient, and solution-processed lighting technologies.

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