Influence of Internal Molecular Motions in the Photothermal Conversion Effect of Charge-Transfer Cocrystals

Herein, we report two new charge-transfer organic cocrystals, CP-TCNQ and CP-TFBQ. The two cocrystals exhibit broad absorption, good thermal stability, and low photoluminescence quantum yields, the necessary requirements to show the photothermal conversion (PTC) effect. Indeed, the two cocrystals exhibit distinct PTC efficiencies of 11.0 ± 1.4% (CP-TCNQ) and 17.0 ± 1.0% (CP-TFBQ). The 55% improvement in the observed efficiencies is attributed to the fast in-plane reorientations of the TFBQ fragment, as determined by detailed ssNMR spectroscopy and DFT calculations. This work provides for the first time experimental and computational evidence that the molecular motion of a cocrystal coformer increases its PTC efficiency, paving the way to the design of new crystalline materials with PTC as a regulated property.