Temperature-Dependent Structural Phase Transition in Rubrene Single Crystals: The Missing Piece from the Charge Mobility Puzzle?

Accurate
structural models for rubrene, the benchmark organic semiconductor,
derived from synchrotron X-ray data in the temperature range of 100–300
K, show that its cofacially stacked tetracene backbone units remain
blocked with respect to each other upon cooling to 200 K and start
to slip below that temperature. The release of the blocked slippage
occurs at approximately the same temperature as the hole mobility
crossover. The blocking between 200 and 300 K is caused by a negative
correlation between the relatively small thermal expansion along the
crystallographic b-axis and the relatively large
widening of the angle between herringbone-stacked tetracene units.
DFT calculations reveal that this blocked slippage is accompanied
by a discontinuity in the variation with temperature of the electronic
couplings associated with hole transport between cofacially stacked
tetracene backbones.

针对作为基准有机半导体的红荧烯（rubrene），基于100~300 K温度范围内同步辐射X射线（synchrotron X-ray）数据构建的精确结构模型表明：其共面堆叠（cofacially stacked）的并四苯骨架单元在降温至200 K时仍保持相互锁定状态，且在该温度以下开始发生滑移。受阻滑移的解除温度与空穴迁移率（hole mobility）拐点温度大致相同。200~300 K区间内的锁定效应，源于沿晶体学b轴（crystallographic b-axis）的微弱热膨胀与人字形堆叠（herringbone-stacked）并四苯单元间夹角的显著增大呈负相关。密度泛函理论（Density Functional Theory, DFT）计算显示，该受阻滑移过程伴随共面堆叠并四苯骨架间空穴传输相关电子耦合随温度变化出现不连续性。