Induced-Fit for Oxygen Adsorption: Flexible Conjugated Microporous Polymers With Self-Adaptive Active Sites for H2O2 Photosynthesis.
Photocatalytic hydrogen peroxide (H2O2) synthesis via oxygen reduction reaction (ORR) offers a sustainable alternative to energy-intensive anthraquinone processes. However, its efficiency is hindered by poor selectivity and instability stemming from reactive superoxide intermediates through the two-step two-electron (2e-) route. Herein, inspired by the "induced-fit" mechanism of enzymes, a strategy of self-adaptive active sites modulation using flexible conjugated polymers engineered with nonplanar linking units was proposed. The flexible conjugated microporous polymers facilitated a transition of O2 adsorption from Pauling-type to Yeager-type. Among the designed polymers, CMP-B4, which was constructed from 4,4'-position-coupled bipyridine units, exhibited optimal geometric matching capability for O2 activation. Specifically, upon the approach of O2, the interaction between the lone-pair electrons of nitrogen atoms in flexible bipyridine unit and π* orbitals of O2 induced a dihedral rotation (e.g., approximately 10° in CMP-B4), playing a key role in promoting the one-step 2e- ORR pathway, thus overcoming the limitations of poor adaptability to diverse O2 adsorption modes and restricted versatility of dual-nitrogen units in the rigid nitrogen-rich polymers. Such configuration of CMP-B4 suppressed the formation of *OOH intermediates and achieved an excellent photocatalytic H2O2 production rate of 6.21 mmol g-1 h-1 under continuous-flow photocatalytic conditions over 24 h.