Tuning Photothermal Properties through Donor–Acceptor Engineering: Pyromellitic Diimide:Tetrathiafulvalene versus Tetracyanoquinodimethane:Tetrathiafulvalene Cocrystals

Organic donor–acceptor cocrystals have emerged as a promising class of photothermal materials owing to their strong charge-transfer interactions, tunable optical properties, and scalable synthesis. Here, we report the synthesis, structural characterization, and photothermal performance of a new cocrystal, pyromellitic diimide:tetrathiafulvalene (PD:TTF), prepared via both liquid-assisted grinding and slow solvent evaporation, and benchmark it against the well-known tetracyanoquinodimethane:tetrathiafulvalene (TCNQ:TTF) system. Single-crystal X-ray diffraction and FTIR spectroscopy reveal that PD:TTF forms parallel donor–acceptor stacks with short S···O contacts indicative of strong charge-transfer interactions. Density functional theory calculations show pronounced band gap narrowing relative to the individual components (0.47 eV for PD:TTF and 0.07 eV for TCNQ:TTF), enabling efficient near-infrared absorption. When embedded in polydimethylsiloxane and irradiated with an 808 nm laser, PD:TTF exhibited tunable photothermal conversion efficiency─lower than TCNQ:TTF but demonstrating the ability to modulate thermal output through acceptor selection. Both cocrystals retained stable performance over multiple heating–cooling cycles and continuous irradiation, underscoring their potential for integration into photothermal systems requiring controlled and durable heat generation.