Enhancing Room-Temperature Spin Lifetimes in Molecular Semiconductors by Designing Intramolecular Dipole Orientations

In spintronics, achieving long spin lifetimes, particularly at room temperature (RT), is a key objective for spin transport materials. Molecular semiconductors (MSCs), with their inherently weak spin relaxation mechanisms, have emerged as promising candidates for realizing long RT spin lifetimes. However, effective strategies to suppress spin relaxation through the design of molecular structures in MSCs are still not well understood, and as a result, spin lifetimes remain limited (≈ 10-µs level at RT). In this study, the impact of intramolecular dipole orientations on spin lifetimes in MSCs has been explored for the first time. Both theoretical and experimental results have demonstrated that dipole orientation influences the hyperfine interaction (HFI) effect (a main causation for spin relaxation), and thus, spin lifetime. By adjusting dipole arrangements through molecular design, it is demonstrated that the poly(2,6-azuleneethynylene) with a regular dipole orientation served to reduce the HFI strength and ultimately extended the spin lifetime to 106 µs in a spintronic device, much higher than that of the random arrangement, setting a new RT record. This work provides new insights into the spin relaxation mechanism and offers a valuable strategy for extending spin lifetimes in MSCs for future RT spintronic applications.