Red-Emitting NDI-Embedded Nanohoop as a Solution-Processable Emitter for Mechanically Reconfigurable Inorganic EL Devices

Nanohoops with radial π-conjugation, such as cycloparaphenylenes (CPPs), exhibit intrinsically large Stokes shifts arising from excited-state symmetry breaking. However, their integration into functional electroluminescent platforms has remained virtually unexplored. Herein, we report the synthesis of a three-fold symmetric naphthalenediimide (NDI)-embedded CPP analogue and its application in inorganic powder electroluminescence (iEL) devices. The incorporation of electron-accepting NDI units extends the emission into the red region (λem = 632 nm, ΦF = 22%, in CHCl₃) with a large Stokes shift of 138 nm (4420 cm⁻¹), which is advantageous for suppressing self-absorption. AC field-driven iEL devices achieved reddish-purple emission via a one-step spectral down-conversion from ZnS emission. Notably, the nanohoop emitter is integrated into the device via a simple solution-coating process by mixing 1 wt% of the dye with ZnS, and the resulting devices retained stable emission even when cut, and mechanically reconfigured into “origami-” and “kirigami-” type architectures, demonstrating a level of mechanical flexibility and low-cost processability that is challenging to achieve with conventional OLEDs. This work establishes a design principle for red-emissive nanohoops and highlights the potential of radially π-conjugated macrocycles as promising red emitters for next-generation EL technologies with mechanical reconfigurability.