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.