# In situ characterization of post-synthetic metalation in porous salt thin films

## TL;DR

Researchers created transparent thin films to study how metalation reactions occur in porous materials, revealing how structure and thickness affect reaction rates.

## Contribution

The study introduces a method to grow optically transparent porous thin films for in situ monitoring of post-synthetic metalation kinetics.

## Key findings

- Thin films with controlled thickness were successfully deposited using layer-by-layer assembly.
- In situ spectroscopy revealed structure- and thickness-dependent metalation kinetics.
- The films retain permanent porosity and allow direct monitoring of metalation reactions.

## Abstract

Post-synthetic metalation and metathesis chemistry are central to rational synthesis of metal–organic frameworks (MOFs) that are unavailable by direct self-assembly. The inherent microcrystallinity and heterogeneous nature of many MOFs renders characterization of the rate, extent, and distribution of post-synthetic modifications challenging. Here we describe the deposition of optically transparent, permanently porous thin films comprised of peripherally carboxylated free-base porphyrins and cationic porous molecular cages. The films are assembled via layer-by-layer growth controlled by coulombic charge pairing, which allows for systematic control over film thickness. The obtained thin films are optically transparent monoliths that retain the permanent porosity of the corresponding porous salts. Post-synthetic metalation of these films with Mn(HMDS)2 affords the corresponding Mn(ii) porphyrin-based materials (HMDS = hexamethyldisilazide). Access to thin films with systematically varied thickness (and thus optical density), combined with in situ spectroscopy, enables the kinetics and extent of metalation to be directly monitored. We demonstrate both structure- and thickness-dependence on metalation kinetics. These results provide a unique window into the molecular-scale mechanisms that underpin materials synthesis.

Controlled growth of porous, optically transparent thin films reveals structure- and thickness-dependent effects and enables in situ study of post-synthetic metalation kinetics.