Manipulating Conical Intersections via a Noncovalent Strategy for Enhanced Photothermal Conversion

Organic photothermal materials (OPMs) utilize efficient nonradiative decay for photothermal conversion, with conical intersections (CIs) playing a crucial role in dissipating excited-state energy. Current strategies for manipulating CIs remain largely confined to covalently bonded systems, leaving noncovalent approaches largely unexplored. Herein, we propose a cocrystal-based noncovalent strategy to modulate CI-mediated nonradiative decay. Specifically, phenoxazine (PXZ) or phenothiazine (PTZ) were paired with 1,2,4,5-tetracyanobenzene (TCNB) to construct robust donor-acceptor (D-A) cocrystals. Crystal structure analysis reveals that cocrystal formation transforms the molecular packing from a herringbone to a parallel arrangement, thereby enabling intermolecular motions. Theoretical calculations uncover a favorable relaxation pathway from the Franck-Condon (FC) region to the CI in PXZ-TCNB, with a relaxation energy ΔE = -16.92 kcal mol^-1. Femtosecond transient absorption (Fs-TA) spectroscopy confirms a rapid 11.16 ps relaxation process, demonstrating effective CI-mediated nonradiative decay. Consequently, both PXZ-TCNB and PTZ-TCNB exhibit significantly enhanced photothermal performance compared with their individual components. Leveraging its excellent photothermal conversion efficiency (PCE), we successfully integrated this material into a thermoelectric generator (TEG) for light-driven power generation and fabricated flexible photothermal films with light-responsive actuation. This work establishes noncovalent engineering as a promising strategy for regulating CI processes and advancing high-performance OPMs.