Emergent Rate Laws for Collective Lying–Standing Transitions

High Resolution Image Download MS PowerPoint Slide Lying–standing transitions in the first molecular monolayer at organic–inorganic interfaces strongly influence interface dipoles, energy-level alignment, and growth modes, yet their collective kinetics remain difficult to predict. Here, we establish a quantitative adsorbate-to-kinetics relationship for such transitions using first-principles-based kinetic Monte Carlo simulations combined with a mean-field-type coarse-graining strategy. Focusing on the prototypical system tetracyanoethylene on Cu(111), we show that the collective transition rate cannot be inferred from any single elementary step but instead emerges from a small set of coupled microscopic processes, including reorientation, adsorption, and diffusion. A local two-step reorientation mechanism captures the diffusion-limited regime, while diffusion of lying molecules accelerates the transition in diffusion-enhanced regimes by sterically suppressing back-reorientation via vacancy–molecule decoupling. This effect is captured by a regime-dependent geometric factor that quantitatively accounts for deviations between single-molecule and collective rate constants. By systematically varying molecular size and footprint ratio, we demonstrate that geometry provides a powerful intrinsic control parameter. While the collective rate scales approximately proportionally with molecular area, increasing the footprint ratio between lying and standing configurations leads to order-of-magnitude accelerations due to enhanced vacancy creation and diffusion-assisted stabilization. Based on these results, we derive an explicit analytical expression for the collective reorientation rate constant that links temperature- and pressure-dependent microscopic rate constants to geometric parameters. The resulting formulation quantitatively reproduces the simulation results across kinetic regimes and provides transferable design principles for engineering lying–standing transition time scales at organic–inorganic interfaces.