Metal-modulated phonon transport in porphyrin-based MOFs

Abstract

Metal centers in porphyrin-based frameworks induce distinct thermal transport behaviors, yet their atomistic origins remain unclear. Here, first-principles calculations combined with machine-learned interatomic potentials are used to reveal lattice thermal conductivity (κ) modulation by metal incorporation in a novel 2D porphyrin framework. The results show that Zn increases κ by ∼37% and Ni reduces it by ∼35%. The mechanism is that metal incorporation changes bond uniformity and strength, which alters structural anharmonicity. The phonon relaxation time (τ) is then regulated, which ultimately tunes κ. Additionally, metal embedding enhances structural stability, which induces a blueshift of low-frequency phonons (<10 THz). This effect offsets the redshift induced by heavy atoms, leading to negligible group velocity changes. Specifically, Zn embedding improves bond uniformity, which prolongs τ to boost low-frequency optical mode transport. In contrast, Ni embedding causes lattice contraction and severe bond weakening, which enhances phonon anharmonicity, lowers τ, and ultimately reduces κ. This work verifies that metal selection is a key strategy for phonon engineering in low-dimensional metal-organic materials.