(262d) Molecular Design of Cooperative Transition for Shape Memory Electronics

Electronics and Photonics

Synthesis and Assembly of Electronic and Photonic Materials - Oral Session (08E05)

Molecular Design of Cooperative Transition for Shape Memory Electronics

Hyunjoong Chung; Ying Diao

Polymorphism is the ability for a compound to adopt multiple crystalline packing states. In the field of organic electronics, polymorphism offers a new avenue for optimizing device performance as slight changes in crystal packing can cause significant impact on charge carrier mobility¹. Polymorphic phase transitions can occur via nucleation and growth or a cooperative transition mechanism. The former is known to be the common mechanism in most polymorphic transitions. The latter is rarely observed in molecular crystals, hence the origin and mechanism are largely unexplored. Similar to martensitic transition studied in metallurgy, cooperative transition exhibits low transition barrier, ultrafast kinetics, and structural reversibility. For the first time, we apply cooperative transition to organic electronics for designing next-generation smart multifunctional materials.

In our work, we discover cooperative transition for the first time in single crystals of two different organic semiconductors. From In situ microscopy, single crystal X-ray diffraction, Raman and NMR spectroscopy and molecular simulations we establish a molecular design rule that rotating bulky side chains trigger cooperative transition. By applying cooperativity to organic electronics, we observe shape memory and function memory effect, or reversible modulation of electronic properties². We further investigate the molecular origin of nucleation and cooperativity³ by comparing the role of two different bulky side chains with identical conjugated cores. The system with the bulkier side chains do not exhibit rotational motion even at high temperatures and displays nucleation and growth, while the one containing slightly less bulkier side chains exhibit fully rotational motion and displays cooperative transition. By understanding the molecular origin of different mechanisms of polymorphic transition, we can tailor the molecular structure for designing novel shape memory electronics with fast switching function modulation.

References

1. Chung, H.; Diao, Y., Polymorphism as an emerging design strategy for high performance organic electronics. Journal of Materials Chemistry C 2016, 4 (18), 3915-3933.
2. Chung, H.; Dudenko, D.; Zhang, F. J.; D'Avino, G.; Ruzie, C.; Richard, A.; Schweicher, G.; Cornil, J.; Beljonne, D.; Geerts, Y.; Diao, Y., Rotator side chains trigger cooperative transition for shape and function memory effect in organic semiconductors. Nature Communications 2018, 9.
3. Chung, H.; Ruzié, C.; Geerts, Y.; Diao, Y. “Investigation of the three-step mechanism and the role of defects in cooperative single-crystal-to-single-crystal transition of a molecular crystal”. Submitted to Crystal Growth & Design, 2018.