Cracking Down on Vapochromic Salts: Unveiling Vapomechanical Stress in Gas-Sorbing Platinum Complexes

This study explores the vapochromic and vapoluminescent behaviors of [Pt(tpy)Cl]PF6 host molecules (tpy = 2,2':6',2''-terpyridine) under acetonitrile (CH3CN) vapor guest, challenging the conventional view that these phenomena arise solely from direct host-guest interactions. Our findings reveal a cooperative mechanism where mechanochromic surface perturbations prime the Pt(II) host for guest incorporation, leading to initial color and luminescence changes prior to significant structural alterations. While the color transition between the yellow [Pt(tpy)Cl]PF6 form and the red/orange [Pt(tpy)Cl]PF6•CH3CN form is reversible, repeated vapor cycling induces a loss of crystallinity, as indicated by diffraction peak broadening and emission shifts. Scanning electron microscopy analyses show mechanical deformations like bending and surface pitting, emphasizing the role of vapomechanical stress in altering optical properties. These insights highlight the need for integrated design strategies in developing robust vapochromic materials for gas sensing applications.