A Long-Wavelength Red-Light-Responsive Hydrogel with Tunable Optical Transparency for High-Resolution Information Display

Abstract

Optical transparency regulation holds great potential for information displays, while achieving high-resolution control still remains a challenge. Light manipulation offers superior spatial precision, but conventional photoactivatable systems based on photochromic groups suffer from considerable self-absorption, leading to incomplete transparency-opaque switching.To overcome this limitation, an optical transparency tunable hydrogel was developed by embedding an azobenzene-based polymer and a triplet photosensitizer (PdTPTBP) into a three-dimensional crosslinked hydrogel. This hydrogel enables highresolution transmittance tuning upon long-wavelength red light irradiation. The key mechanism relies on the reversible photoisomerization of azobenzene moiety, which changes its solubility and aggregation state to alter light scattering and transparency. Crucially, by constructing triplet-triplet energy transfer process with the azobenzene moiety, the PdTPTBP extends the excitation wavelength for the cis-to-trans isomerization to 625 nm, a wavelength outside the intrinsic absorption bands of azobenzene moiety. This design significantly suppresses self-absorption of the azobenzene moiety, widens the transmittance regulation range (23% to 96%), and enhances contrast between transparent and opaque regions. The achievable distinguishable distance between these regions reaches 0.1 mm, revealing a resolution sufficient for high-definition display and demonstrating considerable promise for high-resolution information-display applications.