Photo-Controlled Conductance and Thermopower Switching in a Soft Photochromic Metallo-Supramolecular Polymer via EGaIn Junctions

Photochromic soft metallo-supramolecular materials undergo precise, reversible transformations in structure and electronic properties under light irradiation, offering potential applications in optoelectronics, sensing, and molecular switches. Herein, we report the synthesis, characterization, and investigation of light-induced reversible morphological transformations in a Zn(II)-based photochromic coordination polymer gel (Zn-pcCPG), integrated with a dithienylethene (DTE) unit. Upon UV irradiation (λ = 365 nm), Zn-pcCPG undergoes morphological transformation from nanofibers in the gel state to spherical nanoparticles in the sol state, involving reversible photoswitching with distinct color change. To explore the charge transport properties of these metallo-supramolecular polymers, we created a EGaIn/GaO_X//Zn-pcCPG//Au^TS junction using the nanostructures of Zn-pcCPG on a template-stripped gold substrate (Au^TS) and a soft conformal EGaIn as the top electrode. These measurements show a reversible conductance photoswitching between the "open" and "closed" states of the coordination polymer gel containing a DTE core with an on/off ratio of ≈58 at -1 V. Additionally, we have also demonstrated the on-surface photoswitching of morphology and conductance properties. Interestingly, thermoelectric property measurements reveal a HOMO-dominated charge transport for both "open" and "closed" forms of Zn-pcCPG, with a reversible thermopower switching from +163 μV/K (open form) to +21 μV/K (closed form) and vice versa. By employing UV-Vis and ultraviolet photoelectron spectroscopy measurements, we have explained the experimental conductance and thermopower trends. This is the first study to demonstrate reversible conductance and thermopower switching with morphological transitions in a photochromic coordination polymer gel (pcCPG), paving the way for advancements in CPG-based supramolecular electronics.