Temperature-tunable anisotropic absorption for photo-modulated gas sensing.

This study presents a temperature-tunable and photo-modulated sensing platform based on a polyurethane-azobenzene-carbon black (PAC) composite that supports temperature-dependent narrow molecular absorption features. PAC films fabricated under UV and visible light curing exhibit distinct thermally responsive absorption features arising from strong light-matter coupling within the composite. UV curing promotes azobenzene trans-cis isomerization and molecular asymmetry, leading to narrow, temperature-dependent absorption features associated with azobenzene molecular transitions, whereas visible curing yields broader, excitonic-dominated absorption profiles. Micro-grating patterning induces anisotropic optical coupling, resulting in polarization-dependent absorption enhancement and spectral modulation upon photo-exposure. Additionally, UV-cured gratings show amplified absorption under acetone vapor, attributed to photo-induced polar site activation and enhanced gas-polymer interactions. Temporal coupled-mode theory (TCMT) analysis is used only as a phenomenological fitting tool without implying physical mode confinement. It provides only qualitative trends in orientation-dependent changes. Altogether, the PAC platform synergistically combines photothermal, photochromic, and structural anisotropies to deliver a reconfigurable, multifunctional optical sensing system responsive to temperature and gaseous environments.