Nesting Charge Traps in Nanoporous Photoresponsive Thin Film Enables Molecular Recognition.

The void space of a metal-organic framework (MOF) can, in principle, be chemically programmed to engage selectively with guest molecules through geometric complementarity or specific non-covalent interactions. In this work, we have demonstrated that such molecular recognition can be turned on in an otherwise nonselective porous MOF thin film by the deliberate installation of a charge trap chromophore. The chromophore, naphthaleneimide, formed a donor-acceptor complex with the MOF linker 4,4'-anthracene-9,10-diylbis(ethyne-2,1-diyl))dibenzoic acid (AEBA) when positioned at the nanopore surface. This spatial design rendered nanochannels with high sensitivity to the polarity of adsorbed guest molecules. Photoexcitation of this engineered MOF film on a patterned Au-electrode device promoted efficient exciton dissociation, yielding enhanced photocurrents whose magnitude, dark-to-light switching ratio, and rise dynamics depend decisively on the adsorbed molecules. Notably, these distinct electrical signatures disappeared in the unmodified MOF film, underscoring the essential role of charge-trap design. This strategy provides a generalizable route to activate molecular recognition in nonspecific MOF platforms and heralds new opportunities for sensitive, programmable chemical sensing.