Metal-Node-Dictated Charge-Transfer Pathways Determine Photothermal Efficiency: A TTF-Based Zn-MOF Outperforms Its Co-Analogue Despite Weaker D–A π–π Stacking

Abstract The conventional design of donor–acceptor (D–A)-type metal–organic frameworks (MOFs) for photothermal conversion assumes that close π–π stacking between D–A moieties is essential for efficient charge transfer. Herein, we challenge this paradigm by demonstrating that the electronic configuration of metal nodes – rather than spatial D–A proximity – decisively governs photothermal performance. Using identical TTF-based donors and NDI-based acceptors, we construct two anisostructural MOFs with Zn2+ (d10) and Co2+ (d7) nodes. Single-crystal X-ray diffraction reveals a counterintuitive structural dichotomy: TTFBIPA-Co-MOF exhibits well-defined face-to-face D–A π–π stacking (3.58 Å), whereas TTFBIPA-Zn-MOF lacks such direct stacking. Despite this apparent advantage of Co-MOF in spatial D–A proximity, Zn-MOF paradoxically exhibits superior photothermal performance. The origin lies in metal-node electronic effects: Zn2+ is electronically innocent, preserving intrinsic D–A energy levels and enabling efficient through-space charge transfer. Consequently, TTFBIPA-Zn-MOF achieves broad NIR absorption (extending to 1000 nm), a high photothermal conversion efficiency of 47.5% (808 nm laser), and an excellent solar evaporation rate of 2.45 kg·m–2·h–1 with 96.8% efficiency under 1 sun. In contrast, Co2+ engages in d−π* back-donation that perturbs acceptor energy levels, introduces radiative decay pathways, and suppresses NIR absorption, resulting in lower performance (PCE: 39.4%; evaporation rate: 2.04 kg·m–2·h–1). This work establishes that electronic innocence of metal nodes supersedes spatial D–A stacking, providing a transformative design guideline for high-performance photothermal materials.