# Triplet states enable efficient photocatalytic hydrogen evolution in star-shaped truxene-based nanoparticles

## TL;DR

Researchers created new star-shaped molecules that efficiently produce hydrogen using light, thanks to long-lived triplet states.

## Contribution

This is the first report showing triplet charge-transfer states can mediate photocatalytic hydrogen evolution in donor–acceptor oligomer nanoparticles.

## Key findings

- TxNT nanoparticles show a higher hydrogen evolution rate (54 mmol h−1 g−1) compared to TxBT nanoparticles.
- Triplet charge-transfer states in TxNT nanoparticles lead to more efficient charge separation and reduced recombination.
- Pt deposition is significantly lower on TxBT nanoparticles compared to TxNT nanoparticles.

## Abstract

We have developed two new star-shaped donor–acceptor oligomers, named TxBT and TxNT, with a truxene donor core and either 2,1,3-benzothiadiazole (BT) or a naphtho[1,2-c:5,6-c′]bis[1,2,5]thiadiazole (NT) unit, respectively. Femtosecond transient absorption spectroscopy suggested that both oligomer nanoparticles (NPs) generate long-lived triplet charge-transfer (CT) states following photoexcitation, which undergo reductive quenching by ascorbate. TxNT NPs generate a larger population of reduced species that accumulate and escape recombination compared to TxBT NPs, indicating more efficient charge separation. TxNT NPs show significantly higher hydrogen evolution rate (54 mmol h−1 g−1) compared to TxBT NPs, which is comparable to the performance of the most efficient heterojunction polymer NP systems. Additionally, morphological analysis revealed that Pt deposition was significantly lower on TxBT than on TxNT NPs. These findings highlight the critical role of triplet CT states, tuning molecular energy levels, optimizing excited-state dynamics, and engineering NP architecture to increase photocatalytic hydrogen evolution of organic photocatalysts. To our knowledge, this is the first report where triplet CT states can mediate photocatalytic hydrogen evolution in donor–acceptor oligomer NPs.

Two new star-shaped donor–acceptor oligomers, named TxBT and TxNT, with a truxene donor core and either 2,1,3-benzothiadiazole (BT) or a naphtho[1,2-c:5,6-c′]bis[1,2,5]thiadiazole (NT) unit, respectively, have been developed for photocatalytic hydrogen production.