Probing Structural Dynamics in Thin Films of Responsive Molecular Materials: GIWAXS Study of Anisotropic Thermal Expansion and Solid-State Transformations

Thermosalient materials exhibit dynamic structural transformations under temperature variations, making them promising candidates for applications in actuators, sensors, and flexible electronics. Recently, single crystals of PT-BTD (4,7-bis[5-(4-nonylphenyl)-2-thienyl]-5,6-dimethoxy-2,1,3-benzothiadiazole) have demonstrated remarkable thermosalient behavior, characterized by large anisotropic crystal elongation and reversible mechanical motion. The thermosalient behavior in PT-BTD  is linked to its layered molecular packing and flexible nonyl chains, which facilitate large-scale structural transformations upon heating.

While this phenomenon has been studied in bulk crystals, its behavior in thin-film form remains unexplored, which is the focus of this proposal.  Using Grazing-Incidence Wide-Angle X-ray Scattering (GIWAXS), we will monitor temperature-induced structural transition in thin films of  PT-BTD.  With respect to the thermosalient property, we expect to bridge the knowledge gap between bulk and thin-film structural behavior of PT-BTD, in particular in relation to the anisotropic thermal expansion (in-plane and out-of-plane), temperature-induced structural phase transitions, and the reversibility of the changes upon cooling down the films. Additionally, the study will extend to two PT-BTD derivatives and assess their impact on electrical properties via operando structural and electrical measurements in thin-film transistors.

These findings could pave the way for integrating thermosalient materials into adaptive electronic devices.