Manipulating Conical Intersections via a Noncovalent Strategy for Enhanced Photothermal Conversion

Area of Science:

• Materials Science
• Photochemistry
• Nanotechnology

Background:

• Organic photothermal materials (OPMs) convert light to heat via nonradiative decay, often involving conical intersections (CIs).
• Existing methods to control CIs are limited to covalent bonding, neglecting noncovalent strategies.
• Noncovalent approaches offer an unexplored avenue for tuning CI-mediated energy dissipation in OPMs.

Purpose of the Study:

• To introduce and investigate a cocrystal-based noncovalent strategy for modulating CI-mediated nonradiative decay in OPMs.
• To demonstrate the enhanced photothermal performance of cocrystals compared to individual components.
• To explore the application of these enhanced OPMs in light-driven power generation and flexible photothermal films.

Main Methods:

• Construction of donor-acceptor (D-A) cocrystals using phenoxazine (PXZ) or phenothiazine (PTZ) with 1,2,4,5-tetracyanobenzene (TCNB).
• Crystal structure analysis to determine molecular packing and enable intermolecular motions.
• Theoretical calculations and femtosecond transient absorption (Fs-TA) spectroscopy to study relaxation pathways and decay dynamics.

Main Results:

• Cocrystal formation induced a parallel molecular arrangement, facilitating intermolecular motions.
• Theoretical calculations predicted a favorable relaxation pathway to the CI with significant energy release (-16.92 kcal mol⁻¹).
• Fs-TA spectroscopy confirmed rapid nonradiative decay (11.16 ps), indicating effective CI-mediated energy dissipation.
• PXZ-TCNB and PTZ-TCNB cocrystals showed significantly improved photothermal performance over individual components.
• Successful integration into a thermoelectric generator (TEG) for light-driven power and fabrication of light-responsive flexible films.

Conclusions:

• Noncovalent engineering via cocrystal formation is a viable strategy to regulate CI processes in OPMs.
• This approach leads to enhanced photothermal conversion efficiency (PCE).
• The developed materials show promise for advanced applications in energy harvesting and responsive devices.