Polymorph-Specific Electronic Transduction in WO₃ during Molecular Sensing

Polymorphs are distinct structural forms of the same compound and offer unique opportunities to tailor material properties without altering chemical composition. In particular, the polymorphs of WO₃ have been widely explored for their molecular sensing performance; yet, the mechanistic aspects behind their different chemoresistive properties have remained elusive or poorly understood. Here, we highlight the energetic allocation of transferred charge as a critical aspect for chemoresistive response generation, providing a new perspective beyond more conventional net-transfer metrics, which are usually deployed to investigate gas-solid interactions. To this, we combined operando work function, chemisorption analysis, and in situ spectroscopy with density functional theory calculations on the example of acetone. Both γ- and ε-WO₃ exhibit comparable surface-level activation of acetone, mediated by electron-deficient, coordinatively unsaturated tungsten sites. However, only ε-WO₃ stabilizes analyte-induced electronic states derived from W(5d) orbitals lying just below the conduction band-an energetically favorable region for conductivity modulation under operating conditions. While being associated with marginal work function shifts, these states reflect deeper subsurface electronic rearrangements that may underlie the ε-WO₃'s superior transduction efficiency despite similar receptor chemistry. Our results offer a new framework for rational transducer development rooted in intrinsic electronic structure.