Abstract
Martensitic transition is a solid-state phase transition involving cooperative movement of atoms, mostly studied in metallurgy. The main characteristics are low transition barrier, ultrafast kinetics, and structural reversibility. They are rarely observed in molecular crystals, and hence the origin and mechanism are largely unexplored. Here we report the discovery of martensitic transition in single crystals of two different organic semiconductors. In situ microscopy, single-crystal X-ray diffraction, Raman and nuclear magnetic resonance spectroscopy, and molecular simulations combined indicate that the rotating bulky side chains trigger cooperative transition. Cooperativity enables shape memory effect in single crystals and function memory effect in thin film transistors. We establish a molecular design rule to trigger martensitic transition in organic semiconductors, showing promise for designing next-generation smart multifunctional materials.
Highlights
Martensitic transition is a solid-state phase transition involving cooperative movement of atoms, mostly studied in metallurgy
A single crystal is an ideal platform for studying solid-state-phase transitions[34,35] and revealing structure-charge transport relationship in organic electronic devices[36,37,38,39,40,41]
We focused on the carbons of the tBu side chains (C9, C10, and C11), which appeared on the nuclear magnetic resonance (NMR) spectrum near 32.9 ppm We conducted variable temperature 13C cross-polarization magic angle spinning solid-state NMR spectroscopy for a ditBu-BTBT powder sample
Summary
Martensitic transition is a solid-state phase transition involving cooperative movement of atoms, mostly studied in metallurgy. They demonstrated a more precise controllability of superelasticity than in metal alloys Another example is thermosalient crystals, known as ‘jumping crystals’[11,12], which exhibit near-instantaneous martensitic transition and display the shape memory effect. Su et al.[18] showed that an approximately 100° rotation of the n-butyl group induced a cooperative first-order-phase transition in single crystals of a cobalt(II) complex These studies are limited to one system, and generalizable molecular design rules have not been reported for inducing martensitic transition and switchable physical properties in molecular crystals. Organic semiconductors underpin the rapidly advancing printed electronics technology that promises flexible, light-weight, biointegrated electronics at low cost and high throughput in forms unimagined before[20,21,22,23,24,25] Merging these two research areas by coupling electronic switching and sensing mechanisms with the shape memory effect can open new opportunities in creating shape memory electronics. Toward these design objectives, understanding the origin and mechanism of martensitic transition in molecular crystals is a prerequisite
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