# Advancing Bidirectional Photoswitching of Norbornadienes: Exclusively Light‐Induced Interconversion of Imide‐ and Ortho‐Connected Norbornadiene‐Perylene Diimide Hybrids

## TL;DR

Researchers developed a new photoswitch system using norbornadiene and perylene diimide that can store and release energy using light, with potential applications in solar energy storage.

## Contribution

The study introduces a novel framework for bidirectional, light-induced switching of norbornadiene hybrids without additives.

## Key findings

- NBD-PDI hybrids show high conversion yields in both directions under UV and visible light.
- Linker flexibility is crucial for efficient back-isomerization to NBD.
- The system enables on-demand energy release with good thermal and photo-stability.

## Abstract

The norbornadiene/quadricyclane (NBD/QC) photoswitch is a promising candidate for molecular solar energy storage. Isomerization to the energy‐storing, metastable QC occurs upon UV light irradiation, while the back‐switching can be triggered in various ways. However, inducing complete, on‐demand energy release across multiple switching cycles remains a significant challenge in molecular solar thermal (MOST) research. We demonstrate the implementation of perylene diimide (PDI) as covalently connected, photoactive redox‐catalyst to enable NBD regeneration upon 475 nm irradiation. We investigated the NBD/QC interconversion of several imide‐ and ortho‐connected NBD‐PDI hybrids upon irradiation at 310 nm and 475 nm, revealing that the connection position on PDI only minimally affects the interconversion efficiency. Concentration‐dependent studies identified an alternative intermolecular back‐isomerization mechanism in addition to the previously known intramolecular pathway, for which adequate flexibility of the linker proved crucial for effective back‐isomerization to NBD. This study advances the exclusively photoinduced isomerization of the NBD/QC system within novel NBD‐PDI dyads, establishing a framework for the targeted manipulation of NBD hybrids with potential application in energy storage. The presented switches operate independently, without the need for further additives to facilitate interconversion, which renders them promising candidates for molecular solar energy storage research.

Bidirectional Photoswitching: We report norbornadiene‐perylene diimide (NBD‐PDI) dyads with diverse connectivities, enabling exclusively photoinduced NBD/QC switching. Our findings reveal high conversion yields in both directions, paired with good thermal‐ and photo‐stability. Rapid back‐isomerization to NBD occurs upon visible light irradiation, highlighting the potential for on‐demand energy release in energy storage applications.