Article révisé par les pairs
Résumé : The lattice dynamics of organic semiconducting crystals has a significant role in de- termining their electronic and mechanical properties. A common technique to control these macro- scopic properties is chemically modifying the molecular structure. These modifications are known to change the molecular packing, but their effect on the lattice dynamics is relatively unexplored though it can be equally important to their performance at finite temperatures. Therefore, we in- vestigate how chemical modifications to a core [1]benzothieno[3,2-b]benzothiophene (BTBT) semi- conducting crystal affect the evolution of the crystal structural dynamics with temperature. Our study combines temperature-dependent polarization-orientation (PO) low-frequency Raman mea- surements with first-principles calculations and single-crystal XRD measurements. We show that the chemical modifications can indeed suppress expressions of vibrational anharmonicity in the lat- tice dynamics. Specifically, we detect in BTBT a gradual change in the PO Raman response with temperature, indicating a unique expression of anharmonicity. This anharmonic expression is sup- pressed in all examined chemically modified crystals (ditBu-BTBT and diC8-BTBT, diPh-BTBT, and DNTT). Our findings indicate that π-conjugated chemical modifications suppress anharmonic effects more effectively than alkyl chains.

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