Engineering the electronic and optical properties of 2D porphyrin paddlewheel metal-organic frameworks

TL;DR

This study uses computational methods to engineer the electronic and optical properties of 2D porphyrin-based MOFs, aiming to enhance their photocatalytic efficiency for solar fuel production.

Contribution

It introduces specific structural modifications to tune band structures and optical absorption in 2D porphyrin MOFs for improved photocatalytic performance.

Findings

Varying metal centers alters band alignment.

Partial reduction enhances visible light absorption.

Linker modifications influence charge transfer behavior.

Abstract

Metal organic frameworks (MOFs) are promising photocatalytic materials due to their high surface area and tuneability of their electronic structure. We discuss here how to engineer the band structures and optical properties of a family of two-dimensional (2D) porphyrin-based MOFs, consisting of M tetrakis(4 carboxyphenyl)porphyrin structures (M TCPP, where M = Zn2+ or Co2+) and metal (Co2+, Ni2+, Cu2+ or Zn2+) paddlewheel clusters, with the aim of optimising their photocatalytic behaviour in solar fuel synthesis reactions (water splitting and/or CO2 reduction). Based on density functional theory (DFT) and time-dependent DFT simulations with a hybrid functional, we studied three types of composition/structural modifications: a) varying the metal centre at the paddlewheel or at the porphyrin centre to modify the band alignment; b) partially reducing the porphyrin unit to chlorin, which leads to stronger absorption of visible light; and c) substituting the benzene bridging between the porphyrin and paddlewheel, by ethyne or butadiyne bridges, with the aim of modifying the linker to metal charge transfer behaviour. Our work offers new insights on how to improve the photocatalytic behaviour of porphyrin- and paddlewheel-based MOFs.