Sunscreens as Organic Energy Materials: Macroscopic Heat Release Through Vibrational Relaxation Mechanism

Aminocyclohexenimine (ACHI) derivatives are powerful UV‐absorbing molecules, long recognized for their unique properties as sunscreens. Here, we demonstrate for the first time the macroscopic heat release through the previously proposed vibrational relaxation mechanism at the molecular level. Thin films of four different ACHI derivatives deposited on quartz substrates produced measurable macroscopic temperature increases (up to 15 °C) under UV and simulated solar irradiation and moderate‐to‐excellent photothermal stability (maximum half‐life of 116 h under continuous UV). While drop‐cast films provided proof of concept, spin coating yielded transparent and homogeneous layers that enabled direct monitoring of both thermal and spectroscopic responses in the solid state. These experiments revealed that solid‐state absorption spectra, rather than solution‐phase properties, correlate best with photothermal performance. The combination of transparency, durability, and efficient light‐to‐heat conversion highlights ACHI derivatives as a pioneering family of organic photothermal coatings, with potential applications in energy‐managing and optically transparent technologies such as smart windows.