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.

Automated summary

Accurate structural models for rubrene were derived from synchrotron X-ray data in the temperature range of 100-300 K. The models revealed that the cofacially stacked tetracene backbone units of rubrene remain blocked with respect to each other upon cooling to 200 K and start to slip below that temperature. The blocked slippage occurs at approximately the same temperature as the hole mobility crossover. The study also found a negative correlation between the thermal expansion along the crystallographic b-axis and the widening of the angle between herringbone-stacked tetracene units, which causes the blocking between 200 and 300 K. DFT calculations further showed a discontinuity in the temperature variation of the electronic couplings associated with hole transport between the cofacially stacked tetracene backbones.