A Dielectric Design Strategy Based on a High‐Polarity Aromatic Gel for Water‐Resistant Printable Electroluminescent Devices

Printable alternating‐current electroluminescent (ACEL) devices offer a promising platform for creating flexible displays and interactive sensors. However, their progress is often limited by a persistent materials dilemma: enhancing dielectric polarity increases permittivity but unavoidably heightens water sensitivity, leading to dielectric breakdown in humid or aqueous environments. Herein, we develop a printable aromatic gel dielectric in which polar dipoles are confined within a π–π ‐stacked aromatic network, enabling strong dielectric polarization while suppressing direct interactions with water. This π–π ‐mediated confinement yields high permittivity (κ ≈ 10.14 at 10 kHz), an elevated refractive index (n ≈ 1.603), optical transparency, mechanical compliance, and resistance to water exposure. When integrated into fully printable ACEL devices, the dielectric supports low‐field operation, high luminance, and stable electroluminescence during direct water immersion. The same environmental robustness further enables underwater light emission and simple binary optical signaling. Together, these results show that π–π ‐assisted dipole confinement provides a general materials design strategy for environmentally robust, high‐polarity dielectrics.