Benefitting from the strong intrinsic nonlinear optical (NLO) property of the individual porphyrin molecule, the integration of porphyrin molecules into tightly aligned arrays may lead to intuitively promising high-performance materials of tailorable NLO effect. In order to verify this speculation, we prepare crystalline and highly oriented porphyrin-based surface-supported metal–organic framework nanofilms (SURMOFs) and then characterize their NLO performance. Results reveal that porphyrin-based SURMOFs exhibit the highest saturable absorption (SA) yet recorded with a third-order NLO absorption coefficient up to −10–3 cm/W, about 7 orders stronger than porphyrin solvents in which the porphyrin molecules are disordered, under a certain excitation strength. Further increasing the excitation strength shows that the NLO absorption property of the porphyrin-based SURMOFs can be effectively modulated from SA to reverse saturable absorption, followed by a reemerging SA. The multiple-stage NLO switching is assigned to the interplay of simultaneous one-photon SA, two-photon absorption, and two-photon SA effects. The superior and modulatable NLO property as well as the designable and ordered crystalline structure suggest that porphyrin-based SURMOFs might be employed as a new class of high-performance NLO materials with potential applications in novel optical switches or logic gates to realize the all-optical information process.

Metal−organic frameworks (MOFs) provide a novel strategy to precisely control the alignment of molecules to enhance exciton diffusion for high-performance organic semiconductors. In this paper, we characterize exciton dynamics in highly ordered and crystalline porphyrin MOF nanofilms by time-resolved photoluminescence and femtosecond-resolved transient absorption spectroscopy. Results suggest that porphyrin MOF nanofilms could be a promising candidate for high-performance organic photovoltaic semiconductors in which the diffusion coefficient and diffusion length of excitons are 9.0 × 10 −2 cm 2 s −1 and 16.6 nm, respectively, comparable with or even beyond that of other excellent organic semiconductors. Moreover, by monitoring real-time exciton dynamics it is revealed that excitons in MOF nanofilms undergo high-efficient intermolecular hopping and multiexciton annihilation due to the short intermolecular distance and aligned molecular orientation in MOF structure, thus providing new insights into the underlying physics of exciton dynamics and many-body interaction in molecular assembled systems.

Highly luminescent metal–organic frameworks (MOFs) have recently received great attention due to their potential applications as sensors and light-emitting devices. In these MOFs, the highly ordered fluorescent organic linkers positioning prevents excited-state self-quenching and rotational motion, enhancing their light-harvesting properties. Here, the exciton migration between the organic linkers with the same chemical structure but different protonation degrees in Zr-based MOFs was explored and deciphered using ultrafast laser spectroscopy and density functional theory calculations. First, we clearly demonstrate how hydrogen-bonding interactions between free linkers and solvents affect the twisting changes, internal conversion processes, and luminescent behavior of a benzoimidazole-based linker. Second, we provide clear evidence of an ultrafast energy transfer between well-aligned adjacent linkers with different protonation states inside the MOF. These findings provide a new fundamental photophysical insight into the exciton migration dynamics between linkers with different protonation states coexisting at different locations in MOFs and serve as a benchmark for improving light-harvesting MOF architectures.