# Sodium-based donor–acceptor assemblies featuring thermally activated delayed fluorescence enabled by highly efficient through-space charge transfer

## TL;DR

This paper shows that sodium-based compounds can produce efficient thermally activated delayed fluorescence and be used as photocatalysts, offering a low-cost alternative to precious metal complexes.

## Contribution

The study introduces sodium-based assemblies with TADF and demonstrates their use in Dexter energy transfer for the first time.

## Key findings

- Sodium complexes exhibit TADF with high radiative rates up to 4.5 × 10⁵ s⁻¹.
- Na-based compounds function as visible light photosensitizers in Dexter energy transfer.
- Dynamic behavior and reversible metal–ligand bond dissociation were observed in solution.

## Abstract

Exploring more economical and innovative alternatives to precious 4d and 5d metal complexes used in photocatalysis, OLEDs, or energy conversion has primarily focused on 3d metals, leaving highly abundant alkali metals underexplored. We show that, under stoichiometry control of 1,10-phenanthroline-5-carbonitrile (CNphen) and sodium 2,6-bis(trimethylsilyl)benzenethiolate Na(TMSBT), sodium complexes can be obtained that either form the neutral linear assembly [Na(THF)(CNphen)(TMSBT)]N (Na1D) or {[Na(CNphen)4](TMSBT)}N (Na2D) as a 2D-polymeric arrangement with octahedrally coordinated Na, similar to 18 valence electron transition metal complexes, and the thiolate acting as a counter anion. Na1D and Na2D feature bright visible light absorption and thermally activated delayed fluorescence (TADF) from intra- and intermolecular through-space charge-transfer (1/3TSCT) excited states, respectively, with high radiative rates kTADF up to 4.5 × 105 s−1, unprecedented for alkali metal-based luminophores. Solution studies revealed extensive dynamic behavior, including reversible metal–ligand bond dissociation. However, the Na assemblies show 1/3TSCT emission (λem,max = 555 nm) in solution and for the first time we have successfully employed Na-based compounds as visible light photosensitizers in Dexter energy transfer catalysis. This study demonstrates the critical role of TSCT states in constructing photoactive coordination complexes and indicates underexplored, yet significant, potential of sodium-based luminophores as TADF emitters and earth-abundant photocatalysts.

Through-space charge-transfer in Na-based luminophores leads to efficient TADF, and the triplet states can be harvested for Dexter energy transfer.